DOS 4.00 Technical Reference and Application Programming
DOS 4.00: TECHNICAL REFERENCE AND APPLICATION PROGRAMMING August 6th, 1988 FIRST EDITION (JULY 1988) (c) Copyright International Business Machines Corporation 1981, 1988 All rights reserved. PREFACE AUDIENCE This book is written for programmers who develop applications for IBM Personal Computers and Personal System/2(R) computers.(1) The program developer should be competent on the IBM Personal Computer and/or the Personal System/2 and should be familiar with DOS and at least one personal computer programming language. CONTENT Some parts of the book have been rewritten and reorganized to make reference and system architecture information more concise and to present programming information in a task-oriented manner. Information about new and enhanced functions has been added, providing some guide material. RELATED PUBLICATIONS Other manuals that provide detailed information about DOS 4.00 are: Getting Started with DOS 4.00 Using DOS 4.00 DOS 4.00 Command Reference IBM Keyboard Layouts for Your PC and PS/2 systems. (1) Personal System/2 is a registered trademark of the International Business Machines Corporation. CONTENTS CHAPTER 1. INTRODUCTION TRD41 7 Organization of this Book TRD41 16 New DOS 4.00 Services TRD41 43 The Utilities Diskette TRD41 57 Minimum Hardware Configuration TRD41 79 CHAPTER 2. ACCESSING DISKS TRD42 11 The Disk Format TRD42 20 The Boot Record TRD42 41 The File Allocation Table (FAT) TRD42 49 The Disk Directory TRD42 114 The Data Area TRD42 143 Accessing the Disk TRD42 150 Reading and Writing Data Directly to the Disk TRD42 168 Requesting Drive and Disk Information TRD42 180 CHAPTER 3. ACCESSING FILES WITH FILE HANDLES TRD43 13 Filenames TRD43 48 File Handles TRD43 62 Special File Handles TRD43 88 Reading and Writing Data to a File TRD43 119 Requesting and Specifying File Attributes TRD43 140 Accessing Subdirectories TRD43 152 Accessing Directories TRD43 266 Finding Files in Directories TRD43 282 Requesting and Specifying National Language Support (NLS) TRD43 294 Controlling Network Operations TRD43 307 CHAPTER 4. ACCESSING FILES USING FILE CONTROL BLOCKS TRD44 10 The File Control Block (FCB) TRD44 21 The Extended FCB TRD44 128 The Disk Transfer Area (DTA) TRD44 149 Accessing Files TRD44 172 Accessing Sequential Records TRD44 218 Accessing Random Records TRD44 231 Finding Files in Directories TRD44 250 CHAPTER 5. MANAGING DEVICE I/O TRD45 9 Managing Display I/O TRD45 20 Managing Keyboard I/O TRD45 43 Managing Miscellaneous I/O TRD45 71 Managing File System Activities TRD45 84 Accessing the System Device Drivers' Control Channel TRD45 105 Reading and Writing Data in Binary and ASCII Modes TRD45 155 CHAPTER 6. CONTROLLING PROCESSES TRD46 17 Allocating Memory TRD46 32 DOS 4.00 Memory Management TRD46 47 The DOS 4.00 Memory Map TRD46 71 Identifying a Program at Load Time TRD46 134 The Program Segment TRD46 147 Loading and Executing Overlays TRD46 198 The Parameter Block TRD46 216 Terminating a Program/Subprogram TRD46 260 Loading an Overlay without Executing It TRD46 307 Calling a Command Processor TRD46 328 Responding to Errors TRD46 352 Responding to a Control-Break Action TRD46 379 Requesting and Specifying the System Date and Time TRD46 411 Requesting and Specifying the Interrupt Vectors TRD46 426 CHAPTER 7. CREATING OBJECT CODE LIBRARIES TRD47 15 The IBM Library Manager/2 TRD47 20 Starting the LIB.EXE Utility TRD47 52 Entering Input at the Command Line TRD47 216 Using a Response File TRD47 308 Creating and Maintaining Libraries TRD47 359 Creating a Library File TRD47 364 Modifying a Library File TRD47 395 Combining Libraries TRD47 457 Creating a Cross-Reference Listing TRD47 475 Performing Consistency Checks TRD47 500 Setting the Library Page Size TRD47 513 Library Manager Error Messages TRD47 540 CHAPTER 8. CREATING AN EXECUTABLE FILE TRD48 35 The IBM Linker/2 TRD48 40 Starting the LINK.EXE Program TRD48 56 Entering LINK Input at the Command Line TRD48 246 Using a Response File to Supply LINK Input TRD48 340 Using Linker Options TRD48 436 Preparing Files for CodeView /CODEVIEW TRD48 512 Reserving Paragraph Space /CPARMAXALLOC TRD48 530 Ordering Segments /DOSSEG TRD48 560 Controlling Data Loading /DSALLOCATE TRD48 583 Packing Executable Files /EXEPACK TRD48 607 Viewing the Options List /HELP TRD48 640 Controlling Run File Loading /HIGH TRD48 661 Displaying LINK-Time Information /INFORMATION TRD48 679 Copying Line Numbers to the Map File /LINENUMBERS TRD48 692 Producing a Public Symbol Map /MAP TRD48 731 Ignoring Default Libraries /NODEFAULTLIBRARYSEARCH TRD48 770 Preserving Compatibility /NOGROUPASSOCIATION TRD48 793 Preserving Lowercase /NOIGNORECASE TRD48 807 Setting the Overlay Interrupt /OVERLAYINTERRUPT TRD48 836 Pausing to Change Disks /PAUSE TRD48 856 Setting the Maximum Number of Segments /SEGMENTS TRD48 900 Setting the Stack Size /STACK TRD48 939 Reading the Map File TRD48 976 Creating an Overlaid Version of Your Program TRD48 1032 Specifying an Overlay Structure to LINK TRD48 1050 How LINK Formats the .EXE File TRD48 1075 Ordering Segments TRD48 1083 Segment Combine-Types TRD48 1106 Groups TRD48 1143 Instruction and Data Reference Errors TRD48 1159 Linker Error Messages TRD48 1215 Linker Limits TRD48 1681 CHAPTER 9. CONVERTING FILE FORMATS TRD49 8 The EXE2BIN.EXE Utility TRD49 13 Entering Input to EXE2BIN TRD49 34 Two Types of Conversion TRD49 61 Device Drivers TRD49 66 Standard .COM File TRD49 100 CHAPTER 10. DEBUGGING A PROGRAM TRD410 32 The DEBUG Utility TRD410 37 Starting the DEBUG.COM Program TRD410 46 Entering Commands at the DEBUG Prompt TRD410 67 DEBUG Command Summary TRD410 103 The DEBUG Work Space TRD410 181 A (Assemble) Command TRD410 225 C (Compare) Command TRD410 348 D (Dump) Command TRD410 400 E (Enter) Command TRD410 504 F (Fill) Command TRD410 620 G (Go) Command TRD410 669 H (Hexarithmetic) Command TRD410 771 I (Input) Command TRD410 789 L (Load) Command TRD410 811 M (Move) Command TRD410 919 N (Name) Command TRD410 973 O (Output) Command TRD410 1019 P (Proceed) Command TRD410 1040 Q (Quit) Command TRD410 1090 R (Register) Command TRD410 1113 S (Search) Command TRD410 1263 T (Trace) Command TRD410 1321 U (Unassemble) Command TRD410 1390 W (Write) Command TRD410 1513 XA (EMS Allocate) Command TRD410 1645 XD (EMS Deallocate) Command TRD410 1672 XM (EMS Map) Command TRD410 1699 XS (EMS Status) Command TRD410 1727 DEBUG Error Messages TRD410 1759 CHAPTER 11. WRITING AN INSTALLABLE DEVICE DRIVER TRD411 26 Types of Device Drivers TRD411 39 Character Device Drivers TRD411 48 Block Device Drivers TRD411 55 How DOS 4.00 Installs Device Drivers TRD411 84 The Basic Parts of a Device Driver TRD411 134 The Device Driver Header TRD411 148 The Strategy Routine TRD411 274 The Interrupt Routines TRD411 283 How DOS 4.00 Passes a Request TRD411 300 Responding to Requests TRD411 392 Initialization Request TRD411 456 Media Check Request TRD411 511 Build BPB Request TRD411 630 Input and Output Requests TRD411 815 Nondestructive Input No Wait Request TRD411 879 Character Input and Output Status Requests TRD411 901 Character Input and Output Flush Requests TRD411 935 Open and Close Requests TRD411 951 Removable Media Request TRD411 983 Generic IOCTL Request TRD411 1008 Get Logical Device Request TRD411 1037 Set Logical Device Request TRD411 1055 CLOCK$ Device Driver Example TRD411 1073 APPENDIX A. DOS 4.00 INTERRUPTS TRD412 13 20H Program Terminate TRD412 21 21H Function Request TRD412 41 22H Terminate Address TRD412 46 23H Ctrl-Break Exit Address TRD412 53 24H Critical Error Handler Vector TRD412 83 25H/26H Absolute Disk Read/Write TRD412 287 27H Terminate but Stay Resident TRD412 353 28H-2EH Reserved for DOS 4.00 TRD412 392 2FH Multiplex Interrupt TRD412 396 30H-3FH Reserved for DOS 4.00 TRD412 695 APPENDIX B. DOS 4.00 FUNCTION CALLS TRD413 100 Using DOS 4.00 Function Calls TRD413 219 Program Code Fragments TRD413 230 .COM Programs TRD413 236 DOS 4.00 Registers TRD413 256 Responding to Errors TRD413 340 Extended Error Codes TRD413 355 00H -- Program Terminate TRD413 518 01H -- Console Input with Echo TRD413 546 02H -- Display Output TRD413 581 03H -- Auxiliary Input TRD413 603 04H -- Auxiliary Output TRD413 631 05H -- Printer Output TRD413 655 06H -- Direct Console I/O TRD413 672 07H -- Direct Console Input Without Echo TRD413 720 08H -- Console Input Without Echo TRD413 753 09H -- Display String TRD413 786 0AH -- Buffered Keyboard Input TRD413 815 0BH -- Check Standard Input Status TRD413 848 0CH -- Clear Keyboard Buffer and Invoke a Keyboard Function TRD413 868 0DH -- Disk Reset TRD413 885 0EH -- Select Disk TRD413 904 0FH -- Open File TRD413 937 10H -- Close File TRD413 985 11H -- Search for First Entry TRD413 1022 12H -- Search for Next Entry TRD413 1099 13H -- Delete File TRD413 1149 14H -- Sequential Read TRD413 1193 15H -- Sequential Write TRD413 1240 16H -- Create File TRD413 1286 17H -- Rename File TRD413 1330 19H -- Current Disk TRD413 1380 1AH -- Set Disk Transfer Address TRD413 1400 1BH -- Allocation Table Information TRD413 1425 1CH -- Allocation Table Information for Specific Device TRD413 1453 21H -- Random Read TRD413 1489 22H -- Random Write TRD413 1541 23H -- File Size TRD413 1599 24H -- Set Relative Record Field TRD413 1642 25H -- Set Interrupt Vector TRD413 1668 26H -- Create New Program Segment TRD413 1695 27H -- Random Block Read TRD413 1725 28H -- Random Block Write TRD413 1787 29H -- Parse Filename TRD413 1847 2AH -- Get Date TRD413 1918 2BH -- Set Date TRD413 1946 2CH -- Get Time TRD413 1979 2DH -- Set Time TRD413 2015 2EH -- Set/Reset Verify Switch TRD413 2051 2FH -- Get Disk Transfer Address (DTA) TRD413 2085 30H -- Get DOS Version Number TRD413 2108 31H -- Terminate Process and Remain Resident TRD413 2138 33H -- Get/Set System Value TRD413 2175 35H -- Get Interrupt Vector TRD413 2235 36H -- Get Disk Free Space TRD413 2262 38H -- Get or Set Country Dependent Information TRD413 2318 39H -- Create Subdirectory (MKDIR) TRD413 2431 3AH -- Remove Subdirectory (RMDIR) TRD413 2466 3BH -- Change the Current Directory (CHDIR) TRD413 2498 3CH -- Create a File (CREAT) TRD413 2530 3DH -- Open a File TRD413 2577 3EH -- Close a File Handle TRD413 2812 3FH -- Read from a File or Device TRD413 2840 40H -- Write to a File or Device TRD413 2886 41H -- Delete a File from a Specified Directory (UNLINK) TRD413 2938 42H -- Move File Read Write Pointer (LSEEK) TRD413 2971 43H -- Change File Mode (CHMOD) TRD413 3035 44H -- I/O Control for Devices TRD413 3092 45H -- Duplicate a File Handle (DUP) TRD413 3103 46H -- Force a Duplicate of a Handle (FORCDUP) TRD413 3137 47H -- Get Current Directory TRD413 3170 48H -- Allocate Memory TRD413 3202 49H -- Free Allocated Memory TRD413 3237 4AH -- Modify Allocated Memory Blocks (SETBLOCK) TRD413 3263 4BH -- Load or Execute a Program (EXEC) TRD413 3303 4CH -- Terminate a Process (EXIT) TRD413 3442 4DH -- Get Return Code of a Subprocess (WAIT) TRD413 3466 4EH -- Find First Matching File (FIND FIRST) TRD413 3494 4FH -- Find Next Matching File (FIND NEXT) TRD413 3567 54H -- Get Verify Setting TRD413 3606 56H -- Rename a File TRD413 3628 57H -- Get/Set File's Date and Time TRD413 3669 59H -- Get Extended Error TRD413 3714 5AH -- Create Unique File TRD413 3785 5BH -- Create New File TRD413 3839 5CH -- Lock/Unlock File Access TRD413 3878 5E00H -- Get Machine Name TRD413 3972 5E02H -- Set Printer Setup TRD413 4006 5E03H -- Get Printer Setup TRD413 4051 5F02H -- Get Redirection List Entry TRD413 4096 5F03H -- Redirect Device TRD413 4169 5F04H -- Cancel Redirection TRD413 4259 62H -- Get Program Segment Prefix Address TRD413 4305 65H -- Get Extended Country Information TRD413 4328 66H -- Get/Set Global Code Page TRD413 4451 67H -- Set Handle Count TRD413 4494 68H -- Commit File TRD413 4539 6CH -- Extended Open/Create TRD413 4562 APPENDIX C. I/O CONTROL FOR DEVICES (IOCTL) TRD414 4 44H -- I/O Control for Devices (IOCtl) TRD414 50 APPENDIX D. EXPANDED MEMORY SUPPORT TRD415 3
Chapter 1
CHAPTER 1. INTRODUCTION 7 Organization of this Book 16 New DOS 4.00 Services 43 The Utilities Diskette 57 Minimum Hardware Configuration 79 CHAPTER 1. INTRODUCTION This chapter provides information about this book, including the following: Organization of the book for quick information retrieval New and enhanced DOS 4.00 services Contents of the utilities diskette Minimum hardware configuration. ORGANIZATION OF THIS BOOK This book is organized by logical application program development stages necessary to develop an application program on DOS 4.00. You must: Write the source code for the program Translate the source code to executable code Load and execute the program Debug the program Create object code libraries (optional) Convert your file formats (optional). In addition, the book tells how to make best use of the operating system by writing your own device driver or by using the system extensions. Each chapter describes a particular subject. You do not need to read the entire book to create programs or solve problems. Key topics also can be found by referring to the index and the table of contents. The appendixes contain reference information for quick retrieval. They contain the entire numerical list of DOS 4.00 services, including interrupts, function calls, and device driver services. The Technical Quick Reference contains abbreviated information about interrupts. Function calls are listed, along with input/output information and error codes. NEW DOS 4.00 SERVICES DOS 4.00 replaces IBM DOS Version 3.30 and incorporates all services previously provided by IBM DOS Version 3.30. Major new features include: Enhanced country support Double-byte character support A device driver File system support of large disk media Extended Memory Support (EMS) Performance improvements to the file system. Several function requests within interrupt 21H have been enhanced. THE UTILITIES DISKETTE A utilities diskette is included with this book. It contains a listing of the following utilities, and the description of each utility, to help programmers develop an application program: DEBUG.COM A utility to isolate and determine errors in executable programs. EXE2BIN.EXE A utility to convert executable file formats (.EXE) to .COM formats to make them more compact and, therefore, load more quickly. LIB.EXE A utility that allows the programmer to build and edit object libraries. LINK.EXE A utility to translate object code to executable code. VDISK.ASM A fully documented programming example of a device driver. However, this example does not reflect the current level of VDISK.SYS. MINIMUM HARDWARE CONFIGURATION DOS 4.00 supports the following family of IBM Personal Computers and Personal System/2 computers: The IBM Personal Computer The IBM Personal Computer XT(TM) The IBM Personal Computer XT(TM) Model 286(1) The IBM Personal Computer AT(R) (all versions)(2) The IBM PC Convertible The IBM Personal System/2(R) Model 25 (all versions) The IBM Personal System/2(R) Model 30 (all versions) The IBM Personal System/2(R) Model 50 (all versions) The IBM Personal System/2(R) Model 60 (all versions) The IBM Personal System/2(R) Model 80 (all versions). NOTE: DOS 4.00 does not support the IBM PCjr. The minimum memory requirement is 256KB. (1) Personal Computer XT is a trademark of the International Business Machines Corporation. (2) Personal Computer AT and Personal System/2 are registered trademarks of the International Business Machines Corporation. PART 1. WRITING PROGRAMS
Chapter 9
CHAPTER 9. CONVERTING FILE FORMATS 8 The EXE2BIN.EXE Utility 13 Entering Input to EXE2BIN 34 Two Types of Conversion 61 Device Drivers 66 Standard .COM File 100 CHAPTER 9. CONVERTING FILE FORMATS This chapter describes how to use EXE2BIN.EXE on your utilities diskette to convert an .EXE file to a .COM file format. THE EXE2BIN.EXE UTILITY EXE2BIN is useful if you have a simple .EXE file that doesn't need the DOS preparation that an .EXE file usually requires, such as telling the program its location in memory and setting up a stack for it to use. Converting an .EXE file to a .COM format makes the file more compact and enables it to load faster. To qualify for EXE2BIN conversion, your .EXE file has to meet these criteria: The file format must be a valid .EXE one, as produced by the IBM Linker. Actual code and data in the file (the resident portion of the program) must be less than 64KB. Only one segment can be declared; therefore, the file cannot define a STACK segment. If the file is to be loaded by the DOS 4.00 command processor, the IBM Macro Assembler ORG statement must set the location pointer of the file at 100H. The IBM Macro Assembler END statement must specify the first location as the starting address. ENTERING INPUT TO EXE2BIN Input to EXE2BIN must be entered at the command line and has the following format: Note that the only parameter required by EXE2BIN is the filename of the input file. If you specify only a filename, EXE2BIN looks for a file with an .EXE extension in the current directory of the default drive. The output file created by a successful conversion has the same filename with a .BIN extension. For example, suppose you have a file called MYFILE.EXE in your current working directory that meets EXE2BIN's conversion criteria. To have EXE2BIN convert the file, you can enter: EXE2BIN MYFILE EXE2BIN creates a memory image of MYFILE.EXE and copies it to the output file. The new file named MYFILE.BIN is placed in your current working directory. Of course, you can specify any of these optional parameters. If you specify a drive and path for your input file and do not specify an output specification, the output file is placed on the current drive and directory. NOTE: This is a change from previous versions of DOS. TWO TYPES OF CONVERSION Two types of .EXE file conversion are possible, depending on how the entry point of your program is defined. DEVICE DRIVERS The first type of conversion is for a program that will be loaded at the absolute memory address specified by a user application or by DOS 4.00 at system initialization. An example of this kind of program is a device driver. CS:IP is not specified in the program (the .EXE file header contains 0:0 as the program's entry point). Segment fixups are allowed in this type of conversion. If segment fixups are necessary, (that is, your program contains instructions requiring segment relocation), you are prompted for the fixup value. Here are some examples of code that will cause prompting for fixup values: You have used the SEG operator: symbol1 db "e:\filename",0 symbol2 dw SEG symbol1 ;explicit use of SEG symbol3 dw symbol1 ;implicit use of OFFSET You have used a segment name as an immediate field of instruction: myseg SEGMENT PUBLIC . . . MOV AX,MYSEG ; fixup The fixup value is the absolute segment at which the program is to be loaded. The DOS 4.00 command processor is not capable of properly loading this type of program. STANDARD .COM FILE To produce standard .EXE files that are suitable for EXE2BIN conversion, you must use the Macro Assembler ORG statement to set the location pointer of the file at 100H and specify the first location as the start address in the END statement. ORG 100H START . . . END START When EXE2BIN sees that CS:IP is specified as 0000:100H, it assumes that the file is to be run as a standard .COM file, with the location pointer set at 100H by the ORG statement. No segment fixups are possible because standard .COM files must be segment relocatable. Once the conversion is complete, you may rename the resultant file to a .COM extension. Then the command processor is capable of loading and executing the program in the same manner as the .COM programs supplied on your DOS 4.00 diskette. If your file does not fit one of these two descriptions, or if it is similar to the standard .COM file description but has segment fixups, the following message is displayed: File cannot be converted This message is also displayed if the file is not a valid .EXE file. See the IBM Macro Assembler manual for a comparison of .EXE and .COM file structures. Skeleton structures for .EXE files and .COM files are provided on the MASM diskette.
Chapter 10
CHAPTER 10. DEBUGGING A PROGRAM 32 The DEBUG Utility 37 Starting the DEBUG.COM Program 46 Entering Commands at the DEBUG Prompt 67 DEBUG Command Summary 103 The DEBUG Work Space 181 A (Assemble) Command 225 C (Compare) Command 348 D (Dump) Command 400 E (Enter) Command 504 F (Fill) Command 620 G (Go) Command 669 H (Hexarithmetic) Command 771 I (Input) Command 789 L (Load) Command 811 M (Move) Command 919 N (Name) Command 973 O (Output) Command 1019 P (Proceed) Command 1040 Q (Quit) Command 1090 R (Register) Command 1113 S (Search) Command 1263 T (Trace) Command 1321 U (Unassemble) Command 1390 W (Write) Command 1513 XA (EMS Allocate) Command 1645 XD (EMS Deallocate) Command 1672 XM (EMS Map) Command 1699 XS (EMS Status) Command 1727 DEBUG Error Messages 1759 CHAPTER 10. DEBUGGING A PROGRAM This chapter describes how to use the DEBUG.COM program on the utilities diskette to identify and fix problems in your programs. THE DEBUG UTILITY DEBUG provides a controlled testing environment that enables you to monitor the execution of a program. You can make changes directly to a .COM or an .EXE file and execute the file immediately to determine whether your changes fixed a problem. You do not need to reassemble source code files first. DEBUG allows you to load, alter, or display any file and to execute object files as well. STARTING THE DEBUG.COM PROGRAM To start DEBUG, enter information in the following format: You can enter just the DEBUG command, or you can include a file specification. The parameters parm1 and parm2 represent input and output specifications of the program you are debugging. For example, suppose you wanted to monitor the execution of the DOS 4.00 DISKCOMP utility. You enter: DEBUG DISKCOMP.COM A: B: The DEBUG program loads DISKCOMP into memory and displays the DEBUG prompt: The hyphen (-) tells you DEBUG is ready to accept commands to alter, display, or execute the contents of the program in memory. If you enter just DEBUG without a file specification, you can either work with the present memory contents or you can load a required file into memory using the DEBUG NAME and LOAD commands. ENTERING COMMANDS AT THE DEBUG PROMPT A DEBUG command consists of a single letter, usually followed by one or more parameters. For example, the NAME command is entered at the DEBUG prompt as a single letter followed by a file specification: -N MYPROG A command and its parameters can be entered in uppercase, lowercase, or a combination of both. The command and its parameters can be separated by delimiters; however, delimiters are only required between two consecutive hexadecimal values. Thus, the following DUMP commands are equivalent: dcs:100 110 d cs:100 110 d,cs:100,110 A command is activated only after you press the Enter key. If you want to terminate a command and return to the DEBUG prompt, simultaneously press the Ctrl and Break keys. For commands producing a large amount of output, you can simultaneously press the Ctrl and Num Lock keys (or Pause key if available) to suspend the display and then press any key to restart the display, or you can redirect the command's output to a file. When DEBUG encounters a syntax error in a line, it displays the line with the error identified as follows: d cs:100 CS:100 &hat.error 110 In this example, the DUMP command expects the second address to contain only a hexadecimal offset value. It finds the S, which is not a hexadecimal character. DEBUG COMMAND SUMMARY The table below lists the DEBUG commands and describes the debugging operations you can perform with them. Complete format descriptions and examples for each command can be found starting on page 10-4. +---------------------------------------------------------------------------+ | COMMAND TASK DESCRIPTION | +---------------------------------------------------------------------------+ | A Assemble IBM Macro Assembler statements directly into memory. | | (Assemble) | +---------------------------------------------------------------------------+ | C Compare the contents of two blocks of memory. | | (Compare) | +---------------------------------------------------------------------------+ | D (Dump) Dump the contents of a portion of memory to the display or | | redirect it to a file. | +---------------------------------------------------------------------------+ | E (Enter) Make changes to bytes in memory. | +---------------------------------------------------------------------------+ | F (Fill) Fill a range of memory with byte values. | +---------------------------------------------------------------------------+ | G (Go) Execute the program in memory from one address to the | | breakpoint address and then display the next instruction. | +---------------------------------------------------------------------------+ | H (Hex) Add and subtract two hexadecimal values and display the | | results. | +---------------------------------------------------------------------------+ | I (Input) Display the input in the first byte next to the port. | +---------------------------------------------------------------------------+ +---------------------------------------------------------------------------+ | COMMAND TASK DESCRIPTION | +---------------------------------------------------------------------------+ | L (Load) Load the contents of absolute disk sectors or a file | | specified by the NAME command into memory. | +---------------------------------------------------------------------------+ | M (Move) Copy the contents of a block of memory to another location. | +---------------------------------------------------------------------------+ | N (Name) Set up file control blocks and file specification information | | for LOAD and WRITE commands. | +---------------------------------------------------------------------------+ | O (Output) Send a byte to an output port. | +---------------------------------------------------------------------------+ | P Execute a subroutine call, loop instruction, interrupt, or | | (Proceed) repeat string instruction and return control to DEBUG at the | | next instruction. | +---------------------------------------------------------------------------+ | Q (Quit) End the DEBUG session without saving the debugged program. | +---------------------------------------------------------------------------+ | R Display the contents of registers and the settings of flags. | | (Register) | +---------------------------------------------------------------------------+ | S (Search) Search a range of memory for characters. | +---------------------------------------------------------------------------+ | T (Trace) Execute one or more instructions in your program and display | | the contents of registers and flags after each instruction. | +---------------------------------------------------------------------------+ | U Translate the contents of memory into Assembler-like | | (Unassemble)statements, displaying their addresses and hexadecimal | | values. | +---------------------------------------------------------------------------+ | W (Write) Write the debugged program to absolute disk sectors or to the | | original file loaded with DEBUG. | +---------------------------------------------------------------------------+ | XA Allocate a specified number of expanded memory pages to an | | (Allocate) EMS handle. | +---------------------------------------------------------------------------+ | XD Deallocate an EMS handle. | | (Deallocate) | +---------------------------------------------------------------------------+ | XM (Map) Map an EMS logical page to an EMS physical page from an EMS | | handle. | +---------------------------------------------------------------------------+ | XS Display the status of expanded memory. | | (Status) | +---------------------------------------------------------------------------+ THE DEBUG WORK SPACE When the DEBUG program starts, the registers and flags are set to the following values for the program being debugged: The segment registers (CS, DS, ES, and SS) are set to the bottom of free memory; that is, the first segment after the end of the DEBUG program. The Instruction Pointer (IP) is set to hex 0100. The Stack Pointer (SP) is set to the end of the segment, or the bottom of the transient portion of the program loader, whichever is lower. The segment size at offset 6 is reduced by hex 100 to allow for a stack that size. The remaining registers (AX, BX, CX, DX, BP, SI, and DI) are set to 0. However, if you start the DEBUG program with a file specification, the CX register contains the length of the file in bytes. If the file is greater than 64KB, the length is contained in registers BX and CX (the high portion in BX). The initial state of the flags is: NV UP EI PL NZ NA PO NC The default disk transfer address is set to hex 80 in the code segment. All of available memory is allocated. At this point, the loaded program is unable to allocate memory. .EXE Files If a file loaded by DEBUG has an extension of .EXE, DEBUG does the necessary relocation and sets the segment registers, stack pointer, and instruction pointer to the values defined in the file. The DS and ES registers, however, point to the program segment prefix at the lowest available segment. The BX and CX registers contain the size of the program that is smaller than the file size. The program is loaded at the high end of memory if the appropriate parameter was specified when the linker created the file. .HEX Files If a file loaded by DEBUG has an extension of .HEX, the file is assumed to be in INTEL hex format, and is converted to executable form while being loaded. A (ASSEMBLE) COMMAND PURPOSE Assembles IBM Macro Assembler language statements directly into memory. FORMAT A[address] PARAMETERS address Use any of the following formats: A segment register plus an offset, such as CS:0100 A segment address plus an offset, such as 4BA:0100 An offset only, such as 100. In this case, the default segment is used. COMMENTS All numeric input to the Assemble command is in hexadecimal. The assembly statements you enter are assembled into memory at successive locations, starting with the address specified in address. If no address is specified, the statements are assembled into the area at CS:0100, if no previous Assemble command was used, or into the location following the last instruction assembled by a previous Assemble command. After all desired statements have been entered, press the Enter key when you are prompted for the next statement to return to the DEBUG prompt. DEBUG responds to invalid statements by displaying: &hat.error and re-displaying the current assemble address. DEBUG supports standard 8086/8088 assembly language syntax (and the 8087 instruction set), with the following rules: All numeric values entered are hexadecimal and can be entered as 1 through 4 characters. Prefix mnemonics are entered in front of the opcode to which they refer. They can also be entered on a separate line. The segment override mnemonics are CS:, DS:, ES:, and SS:. String manipulation mnemonics must specify the string size. For example, MOVSW must be used to move word strings and MOVSB must be used to move byte strings. The mnemonic for the far return is RETF. The assembler will automatically assemble short, near, or far jumps and calls depending on byte displacement to the destination address. These can be overridden with the NEAR or FAR prefix. For example: 0100:0500 JMP 502 ;a 2 byte short jump 0100:0502 JMP NEAR 505 ;a 3 byte near jump 0100:0505 JMP FAR 50A ;a 5 byte far jump The NEAR prefix can be abbreviated to NE, but the FAR prefix cannot be abbreviated. DEBUG cannot tell whether some operands refer to a word memory location or a byte memory location. In this case, the data type must be explicitly stated with the prefix WORD PTR or BYTE PTR. DEBUG will also accept the abbreviations WO and BY. For example: NEG BYTE PTR [128] DEC WO [SI] DEBUG also cannot tell whether an operand refers to a memory location or to an immediate operand. DEBUG uses the common convention that operands enclosed in square brackets refer to memory. For example: MOV AX,21 ;Load AX with 21H MOV AX,[21] ;Load AX with the contents of memory location 21H Two popular pseudo-instructions have also been included. The DB opcode assembles byte values directly into memory. The DW opcode assembles word values directly into memory. For example: DB 1,2,3,4,'THIS IS AN EXAMPLE' DB 'THIS IS A QUOTE: '' DB 'THIS IS AN APOSTROPHE:'' DW 1000,2000,3000,'BACH:' All forms of the register indirect commands are supported. For example: ADD BX,34[BP+2][SI-1] POP [BP+DI] PUSH [SI] All opcode synonyms are supported. For example: LOOPZ 100 LOOPE 100 JA 200 JNBE 200 For numeric co-processor opcodes the WAIT or FWAIT prefix must be explicitly specified. For example: FWAIT FADD ST,ST(3) ;This line will ;assemble a ;FWAIT prefix FLD TBYTE PTR [BX] ;This line will ;not EXAMPLE C>debug -a200 08B4:0200 xor ax,ax 08B4:0202 mov [bx],ax 08B4:0204 ret 08B4:0205 C (COMPARE) COMMAND PURPOSE Compares the contents of two blocks of memory. FORMAT C range address PARAMETERS range Either of these two formats: An address followed by an offset, such as CS:100 110. An address followed by L value, where value is the number of hexadecimal bytes to be processed. For example, CS:100 L 10. The limit for range is hexadecimal 10000 or decimal 64KB. To specify a range of 64KB within 4 hexadecimal characters, enter 0000 or 0 for value. address Any of these three formats: A segment register plus an offset, such as CS:0100. A segment address plus an offset, such as 4BA:0100. An offset only, such as 100. In this case, the default segment is used. COMMENTS The contents of the two blocks of memory are compared; the length of the comparison is determined from the range. If unequal bytes are found, their addresses and contents are displayed, in the form: addr1 byte1 byte2 addr2 where, the first half (addr1 byte1) refers to the location and contents of the mismatching locations in range, and the second half (byte2 addr2) refers to the byte found in address. If you enter only an offset for the beginning address of range, the C command assumes the segment contained in the DS register. To specify an ending address for range, enter it with only an offset value. EXAMPLE C 100 L20 200 The 32 bytes (hex 20) of memory beginning at DS:100 are compared with the 32 bytes beginning at DS:200. L20 is the range. D (DUMP) COMMAND PURPOSE Displays the contents of a portion of memory. FORMAT D [address] or D [range] PARAMETERS address Any of the following formats: A segment register plus an offset, such as CS:0100. A segment address plus an offset, such as 4BA:0100. An offset only, such as 100. In this case, the default segment is used. range Either of these two formats: An address followed by an offset, such as CS:100 110. An address followed by L value, where value is the number of hexadecimal bytes to be processed. For example, CS:100 L 10. The limit for range is hexadecimal 10000 or decimal 64K bytes. To specify a range of 64K bytes within 4 hexadecimal characters, enter 0000 or 0 for value. COMMENTS The dump is displayed in two parts: 1. A hexadecimal portion. Each byte is displayed in hexadecimal. 2. An ASCII portion. The bytes are displayed as ASCII characters. Unprintable characters (ASCII 0 to 31 and 127 to 255) are indicated by a period. With a 40-column system display format, each line begins on an 8-byte boundary and shows 8 bytes. With an 80-column system display format, each line begins on a 16-byte boundary and shows 16 bytes. There is a hyphen between the 8th and 9th bytes. NOTE: The first line may have fewer than 8 or 16 bytes if the starting address of the dump is not on a boundary. In this case, the second line of the dump begins on a boundary. The Dump command has two format options. OPTION 1 Use this option to display the contents of hex 40 bytes (40-column mode) or hex 80 bytes (80-column mode). For example: D address or D The contents are dumped starting with the specified address. If you do not specify an address, the D command assumes the starting address is the location following the last location displayed by a previous D command. Thus, it is possible to dump consecutive 40-byte or 80-byte areas by entering consecutive D commands without parameters. If no previous D command was entered, the location is offset hex 100 into the segment originally initialized in the segment registers by DEBUG. NOTE: If you enter only an offset for the starting address, the D command assumes the segment contained in the DS register. OPTION 2 Use this option to display the contents of the specified address range. For example: D range NOTE: If you enter only an offset for the starting address, the D command assumes the segment contained in the DS register. If you specify an ending address, enter it with only an offset value. For example: D cs:100 10C A 40-column display format might look like this: 04BA:0100 42 45 52 54 41 20 54 00 BERTA T. 04BA:0108 20 42 4F 52 47 BORG E (ENTER) COMMAND PURPOSE Replaces the contents of one or more bytes, starting at the specified address, with the values contained in the list (see Option 1). Displays and allows modification of bytes in a sequential manner (see Option 2). FORMAT E address [list] PARAMETERS address Any of the following formats: A segment register plus an offset, such as CS:0100. A segment address plus an offset, such as 4BA:0100. An offset only, such as 100. In this case, the default segment is used. list A string of byte values. If you include a character string, enclose the characters in single or double quotation marks. To specify a quotation mark as a character within the string when it is also used to delimit the string, type it twice. 'These ''quotes'' are correct.' 'This one''s okay, too.' COMMENTS If you enter only an offset for the address, the E command assumes the segment contained in the DS register. The Enter command has two format options. OPTION 1 Use this option to place the list in memory beginning at the specified address. E address list For example: E ds:100 F3 'xyz' 8D Memory locations ds:100 through ds:104 are filled with the 5 bytes specified in the list. OPTION 2 Use this option to display the address and the byte of a location, then the system waits for your input. For example: E address Enter a 1- or 2-character hexadecimal value to replace the contents of the byte; then take any one of the following actions: 1. Press the space bar to advance to the next address. Its contents are displayed. If you want to change the contents take option 1, above. To advance to the next byte without changing the current byte, press the space bar again. 2. Enter a hyphen to back up to the preceding address. A new line is displayed with the preceding address and its contents. If you want to change the contents, take option 1, above. To back up one more byte without changing the current byte, enter another hyphen. 3. Press the Enter key to end the Enter command. NOTE: Display lines can have 4 or 8 bytes of data, depending on whether the system display format is 40- or 80-column. Spacing beyond an 8-byte boundary causes a new display line, with the beginning address, to be started. For example: E cs:100 might cause this display: 04BA:0100 EB. To change the contents of 04BA:0100 from hex EB to hex 41, enter 41. 04BA:0100 EB.41 To see the contents of the next three locations, press the space bar three times. The screen might look like this: 04BA:0100 EB.41 10. 00. BC. To change the contents of the current location (04BA:0103) from hex BC to hex 42, enter 42. 04BA:0100 EB.41 10. 00. BC.42 Now, suppose you want to back up and change the hex 10 to hex 6F. This is what the screen looks like after entering two hyphens and the replacement byte: 04BA:0100 EB.41 10.00. BC.42- 04BA:0102 00.- 04BA:0101 10.6F Press the Enter key to end the Enter command. The hyphen prompt will appear. F (FILL) COMMAND PURPOSE Fills the memory locations in the range with the values in the list. FORMAT F range list PARAMETERS range Either of these two formats: An address followed by an offset, such as CS:100 110 An address followed by L value, where value is the number of hexadecimal bytes to be processed. For example, CS:100 L 10. The limit for range is hexadecimal 10000 or decimal 64K bytes. To specify a range of 64K bytes within 4 hexadecimal characters, enter 0000 or 0 for value. list A string of byte values. If you include a character string, enclose the characters in single or double quotation marks. To specify a quotation mark as a character within the string when it is also used to delimit the string, type it twice. 'These ''quotes'' are correct.' 'This one''s okay, too.' COMMENTS If the list contains fewer bytes than the address range, the list is used repeatedly until all the designated memory locations are filled. If the list contains more bytes than the address range, the extra list items are ignored. NOTE: If you enter only an offset for the starting address of the range, the Fill command assumes the segment contained in the DS register. EXAMPLE F 4BA:100 L 5 F3 'XYZ' 8D Memory locations 04BA:100 through 04BA:104 are filled with the 5 bytes specified. Remember that the ASCII values of the list characters are stored. Thus, locations 100-104 will contain F3 58 59 5A 8D. G (GO) COMMAND PURPOSE Executes the program you are debugging. Stops the execution when the instruction at a specified address is reached (breakpoint), and displays the registers, flags, and the next instruction to be executed. FORMAT G [=address] [address [address...]] PARAMETERS address Any of the following formats: A segment register plus an offset, such as CS:0100. A segment address plus an offset, such as 4BA:0100. An offset only, such as 100. In this case, the default segment is used. COMMENTS Program execution begins with the current instruction, whose address is determined by the contents of the CS and IP registers, unless overridden by the =address parameter (the = must be entered). If =address is specified, program execution begins with CS:=address. The Go command has two format options. OPTION 1 Use this option to execute the program you are debugging without breakpoints. For example: G [=address] This option is useful when testing program execution with different parameters each time. (Refer to the Name command.) Be certain the CS:IP values are set properly before issuing the G command, if not using =address. OPTION 2 This option performs the same function as Option 1 but, in addition, allows breakpoints to be set at the specified addresses. For example: G [=address] address [address...] This method causes execution to stop at a specified location so the system or program environment can be examined. You can specify up to ten breakpoints in any order. You may wish to take advantage of this if your program has many paths, and you want to stop the execution no matter which path the program takes. The DEBUG program replaces the instruction codes at the breakpoint addresses with an interrupt code (hex CC). If any one breakpoint is reached during execution, the execution is stopped, the registers and flags are displayed, and all the breakpoint addresses are restored to their original instruction codes. If no breakpoint is reached, the instructions are not restored. NOTES: 1. Once a program has reached completion (DEBUG has displayed the "Program terminated normally" message), you must reload the program before it can be executed again. 2. Make sure that the address parameters refer to locations that contain valid 8086/8088 instruction codes. If you specify an address that does not contain valid instruction in the first byte, unpredictable results occur. 3. The stack pointer must be valid and have 6 bytes available for the Go command, otherwise, unpredictable results occur. 4. If only an offset is entered for a breakpoint, the G command assumes the segment contained in the CS register. 5. Do not set breakpoints at instructions in read-only memory (ROM BIOS or ROM BASIC). For example: G 102 1EF 208 Be careful not to set a breakpoint between a segment override indication (such as ES; alone on a line), and the instruction that the override qualifies. Execution begins with the current instruction, whose address is the current values of CS:IP. The =address parameter was not used. Three breakpoints are specified; assume that the second is reached. Execution stops before the instruction at location CS:1EF is executed, the original instruction codes are restored, all three breakpoints are removed, the display occurs, and the Go command ends. Refer to the Register command for a description of the display. H (HEXARITHMETIC) COMMAND PURPOSE Adds the two hexadecimal values, then subtracts the second from the first. Displays the sum and difference on one line. FORMAT H value value EXAMPLE H 0F 8 0017 0007 The hexadecimal sum of 000F and 0008 is 0017, and their difference is 0007. I (INPUT) COMMAND PURPOSE Inputs and displays (in hexadecimal) 1 byte from the specified port. FORMAT I portaddress PARAMETERS portaddress A 1-4 character hexadecimal value specifying an 8- or 16-bit port address. EXAMPLE I 2F8 6B The single hexadecimal byte read from port 02F8 is displayed (6B). L (LOAD) COMMAND PURPOSE Loads a file or absolute disk sectors into memory. FORMAT L [address[drive sector sector]] PARAMETERS address Any of the following formats: A segment register plus an offset, such as CS:0100. A segment address plus an offset, such as 4BA:0100. An offset only, such as 100. In this case, the default segment is used. drive A decimal number that indicates a particular drive. For example, drive A is 0, drive B is 1, and so on. sector 1-3 character hexadecimal values that specify the starting relative sector number and the number of sectors to be loaded or written. NOTE: Relative sector numbers are obtained by counting the sectors on the disk surface. The first sector on the disk is at track 0, sector 1, head 0, and is relative sector 0. The numbering continues for each sector on that track and head, then continues with the first sector on the next head of the same track. When all sectors on all heads of the track have been counted, numbering continues with the first sector on head 0 of the next track. COMMENTS The maximum number of sectors that can be loaded with a single Load command is hex 80. A sector contains 512 bytes. NOTE: DEBUG displays a message if a disk read error occurs. You can retry the read operation by pressing the F3 key to re-display the Load command. Then press the Enter key. The Load command has two format options. OPTION 1 Use this option to load data from the disk specified by drive and place the data in memory beginning at the specified address. For example: L address drive sector sector The data is read from the specified starting relative sector (first sector) and continues until the requested number of sectors is read (second sector). NOTE: If you only enter an offset for the beginning address, the L command assumes the segment contained in the CS register. For example, to load data, you might enter: L DS:100 1 0F 6D The data is loaded from the diskette in drive B and placed in memory beginning at DS:100. Consecutive sectors of data are transferred, 6DH (109), starting with relative sector hex 0F (15) (the 16th sector on the diskette). NOTE: Option 1 cannot be used if the drive specified is a network drive. OPTION 2 When issued without parameters, or with only the address parameter, use this option to load the file whose file specification is at CS:80. For example: L or L address This condition is met by specifying the file name when starting the DEBUG program, or by using the Name command. NOTE: If DEBUG was started with a file specification and subsequent Name commands were used, you may need to enter a new Name command for the proper file specification before issuing the Load command. The file is loaded into memory beginning at CS:100 (or the location specified by address), and is read from the drive specified in the file specification, or from the default drive, if none was specified. Note that files with extensions of .COM or .EXE are always loaded at CS:100. If you specified an address, it is ignored. The BX and CX registers are set to the number of bytes read; however, if the file being loaded has an extension of .EXE, the BX and CX registers are set to the actual program size. The file may be loaded at the high end of memory. Refer to "The DEBUG Work Space" on page 10-3 for the conditions that are in effect when .EXE or .HEX files are loaded. For example: DEBUG -N myprog -L The file named MYPROG is loaded from the default directory and placed in memory beginning at location CS:0100. M (MOVE) COMMAND PURPOSE Moves the contents of the memory locations specified by range to the locations beginning at the address specified. FORMAT M range address PARAMETERS range Either of these two formats: An address followed by an offset, such as CS:100 110. An address followed by L value, where value is the number of hexadecimal bytes to be processed. For example, CS:100 L 10. The limit for range is hexadecimal 10000 or decimal 64KB. To specify a range of 64KB within 4 hexadecimal characters, enter 0000 or 0 for value. address Any of the following formats: A segment register plus an offset, such as CS:0100. A segment address plus an offset, such as 4BA:0100. An offset only, such as 100. In this case, the default segment is used. COMMENTS Overlapping moves are always performed without loss of data during the transfer. (The source and destination areas share some of the same memory locations.) The data in the source area remains unchanged unless overwritten by the move. NOTES: 1. If you enter only an offset for the beginning address of the range, the M command assumes the segment contained in the DS register. If you specify an ending address for the range, enter it with only an offset value. 2. If you enter only an offset for the address of the destination area, the M command assumes the segment contained in the DS register. EXAMPLE M CS:100 L10 500 The 17 bytes of data from CS:100 through CS:110 are moved to the area of memory beginning at DS:500. N (NAME) COMMAND PURPOSE Formats file control blocks for the first two file specifications, at CS:5C and CS:6C. (Starting DEBUG with a file specification also formats a file control block at CS:5C.) The file control blocks are set up for the Load and Write commands and to supply required file names for the program being debugged. All file specifications and other parameters, including delimiters, are placed exactly as entered in a parameter save area at CS:81, with CS:80 containing the number of characters entered. Register AX is set to indicate the validity of the drive specifiers entered with the first two file specifications. FORMAT N [d:][path]filename[.ext] COMMENTS If you start the DEBUG program without a file specification, you must use the Name command before a file can be loaded with the L command. EXAMPLE DEBUG -N myprog -L To define file specifications or other parameters required by the program being debugged, enter: DEBUG myprog -N file1 file2 In this example, DEBUG loads the file MYPROG at CS:100, and leaves the file control block at CS:5C formatted with the same file specification. Then, the Name command formats file control blocks for file1 and file2 at CS:5C and CS:6C, respectively. The file control block for MYPROG is overwritten. The parameter area at CS:81 contains all characters entered after the N, including all delimiters, and CS:80 contains the count of those characters (hex 0C). O (OUTPUT) COMMAND PURPOSE Sends the byte to the specified output port. FORMAT O portaddress byte PARAMETERS portaddress A 1-4 character hexadecimal value specifying an 8- or 16-bit port address. EXAMPLE To send the byte value 4F to output port 2F8, enter: O 2F8 4F P (PROCEED) COMMAND PURPOSE Causes the execution of a subroutine call, a loop instruction, an interrupt, or a repeat string instruction to stop at the next instruction. FORMAT P[=address][value] PARAMETERS address Any of the following formats: A segment register plus an offset, such as CS:0100. A segment address plus an offset, such as 4BA:0100. An offset only, such as 100. In this case, the default segment is used. value A 1-4 character hexadecimal value, specifying the number of instructions to execute. COMMENTS When at a subroutine call, a loop instruction, an interrupt, or a repeat string instruction, issue the Proceed command to execute the instruction (perform the entire function), and return control at the next instruction. The Proceed command has the same syntax as the Trace command. Specifying P0 is the same as specifying T0. EXAMPLE If the following instructions are executed: 0100 CALL 1000 0103 JC 2000 . . . 1000 XOR AX,AX . . . 1XXX RET And if CS:IP was pointing to the CALL 1000 instruction, typing P causes the execution of the subroutine and returns control to DEBUG at the JC instruction. Q (QUIT) COMMAND PURPOSE Ends the DEBUG program. FORMAT Q COMMENTS The file that you are working on in memory is not saved by the Quit command. You must use the Write command to save the file. DEBUG returns to the command processor which then issues the normal command prompt. EXAMPLE -Q A> R (REGISTER) COMMAND PURPOSE The Register command has the following three functions: Displays the hexadecimal contents of a single register with the option of changing those contents Displays the hexadecimal contents of all the registers, plus the alphabetic flag settings, and the next instruction to be executed Displays the eight 2-letter alphabetic flag settings with the option of changing any or all of them. FORMAT R [registername] PARAMETERS registername The valid names are: AX SP CS IP BX BP DS F CX SI ES DX DI SS IP refers to the instruction pointer, and F refers to the flags register. COMMENTS When the DEBUG program starts, the registers and flags are set to certain values for the program being debugged. (Refer to "The DEBUG Work Space" on page 10-3.) DISPLAY A SINGLE REGISTER To display the contents of a single register, enter the register name: R AX The system might respond with: AX F1E4 : Now you can take one of two actions: press the Enter key to leave the contents unchanged, or change the contents of the AX register by entering a 1-4 character hexadecimal value, such as hex FFF. AX F1E4 :FFF Now, pressing the Enter key changes the contents of the AX register to hex 0FFF. DISPLAY ALL REGISTERS AND FLAGS To display the contents of all registers and flags and the next instruction to be executed, type: R The system responds: AX=0E00 BX=00FF CX=0007 DX=01FF SP=039D BP=0000 SI=005C DI=0000 DS=3D5B ES=3D5B SS=3D5B CS=3D5B IP=011A NV UP EI PL NZ NA PO NC 3D5B:011A CD21 INT 21 The first four lines display the hexadecimal contents of the registers and the eight alphabetic flag settings. The last line indicates the location of the next instruction to be executed and its hexadecimal and unassembled formats. This is the instruction pointed to by CS:IP. A system with an 80-column display shows: 1st line - 8 registers 2nd line - 5 registers and 8 flag settings 3rd line - next instruction information A system with a 40-column display shows: 1st line - 4 registers 2nd line - 4 registers 3rd line - 4 registers 4th line - 1 register and 8 flag settings 5th line - next instruction information Display All Flags There are eight flags, each with two-letter codes to indicate either a set condition or a clear condition. The flags appear in displays in the order shown in the following table: +---------------------------------------------------------------------------+ | FLAG NAME SET CLEAR | +---------------------------------------------------------------------------+ | Overflow (yes/no) OV NV | +---------------------------------------------------------------------------+ | Direction (decrease/increase) DN UP | +---------------------------------------------------------------------------+ | Interrupt (enable/disable) EI DI | +---------------------------------------------------------------------------+ | Sign (negative/positive) NG PL | +---------------------------------------------------------------------------+ | Zero (yes/no) ZR NZ | +---------------------------------------------------------------------------+ | Auxiliary carry (yes/no) AC NA | +---------------------------------------------------------------------------+ | Parity (even/odd) PE PO | +---------------------------------------------------------------------------+ | Carry (yes/no) CY NC | +---------------------------------------------------------------------------+ To display all flags, enter: R F If all the flags are in a set condition, the response is: OV DN EI NG ZR AC PE CY - Now you can either press the Enter key to leave the settings unchanged or change any or all of the settings. To change a flag, just enter its opposite code. The opposite codes can be entered in any order with or without intervening spaces. For example, to change the first, third, fifth, and seventh flags, enter: OV DN EI NG ZR AC PE CY - PONZDINV The changes in this example are entered in reverse order. Press the Enter key and the flags are modified as specified, the prompt appears, and you can enter the next command. If you want to see if the new codes are in effect, enter: R F The response is: NV DN DI NG NZ AC PO CY - The first, third, fifth, and seventh flags are changed as requested. The second, fourth, sixth, and eighth flags are unchanged. A single flag can be changed only once for each R F command. S (SEARCH) COMMAND PURPOSE Searches the range for the character(s) in the list. FORMAT S range list range Either of these two formats: An address followed by an offset, such as CS:100 110. An address followed by L value, where value is the number of hexadecimal bytes to be processed. For example, CS:100 L 10. The limit for range is hexadecimal 10000 or decimal 64KB. To specify a range of 64KB within 4 hexadecimal characters, enter 0000 or 0 for value. list A string of byte values. If you include a character string, enclose the characters in single or double quotation marks. To specify a quotation mark as a character within the string when it is also used to delimit the string, type it twice. 'These ''quotes'' are correct.' 'This one''s okay, too.' COMMENTS All matches are indicated by displaying the addresses where matches are found. A display of the prompt without an address means that no match was found. NOTE: If you enter only an offset for the starting address of the range, the S command assumes the segment contained in the DS register. EXAMPLE If you want to search the range of addresses from CS:100 through CS:110 for hex 41, type: S CS:100 110 41 If two matches are found the response might be: 04BA:0104 04BA:010D If you want to search the same range of addresses for a match with the 4-byte list (41 'AB' E), enter: S CS:100 L 11 41 'AB' E The starting addresses of all matches are listed. If no match is found, no address is displayed. T (TRACE) COMMAND PURPOSE Executes one or more instructions starting with the instruction at CS:IP, or at =address, if it is specified. The = must be entered. One instruction is assumed, but you can specify more than one with value. This command displays the contents of all registers and flags after each instruction executes. For a description of the display format, refer to the Register command. FORMAT T [=address][value] PARAMETERS address Any of the following formats: A segment register plus an offset, such as CS:0100. A segment address plus an offset, such as 4BA:0100. An offset only, such as 100. In this case, the default segment is used. value A 1-4 character hexadecimal value, specifying the number of instructions to execute. COMMENTS The display caused by the Trace command continues until value instructions are executed. Therefore, when tracing multiple instructions, remember you can suspend the scrolling at any time by pressing the Ctrl and the NumLock keys together, or the Pause key. Resume scrolling by entering any other character. NOTES: 1. The Trace command disables all hardware interrupts before executing the user instruction, and then re-enables the interrupts when the trap interrupt occurs following the execution of the instruction. 2. TRACE should not be used with any steps that change the contents of the 8259 interrupt mask (ports 20 and 21). 3. If you trace an INT3 instruction, the breakpoint is set at the INT3 location. EXAMPLE T If the IP register contains 011A, and that location contains B40E (MOV AH,0EH), this may be displayed: AX=0E00 BX=00FF CX=0007 DX=01FF SP=039D BP=0000 SI=005C DI=0000 DS=3D5B ES=3D5B SS=3D5B CS=3D5B IP=011C NV UP EI PL NZ NA PO NC 3D5B:011C CD21 INT 21 This displays the results after the instruction at 011A is executed, and indicates the next instruction to be executed is the INT 21 at location 04BA:011C. T 10 Sixteen instructions are executed (starting at CS:IP). The contents of all registers and flags are displayed after each instruction. The display stops after the 16th instruction has been executed. Displays may scroll off the screen unless you suspend the display by simultaneously pressing the Ctrl and NumLock keys, or the Pause key. U (UNASSEMBLE) COMMAND PURPOSE Unassembles instructions (that is, translates the contents of memory into assembler-like statements) and displays their addresses and hexadecimal values, together with assembler-like statements. For example, a display might look like this: 04BA:0100 206472 AND [SI+72],AH 04BA:0103 FC CLD 04BA:0104 7665 JBE 016B FORMAT U [address] or U [range] PARAMETERS address Any of the following formats: A segment register plus an offset, such as CS:0100. A segment address plus an offset, such as 4BA:0100. An offset only, such as 100. In this case, the default segment is used. range Either of these two formats: An address followed by an offset, such as CS:100 110. An address followed by L value, where value is the number of hexadecimal bytes to be processed. For example, CS:100 L 10. The limit for range is hexadecimal 10000 or decimal 64KB. To specify a range of 64KB within 4 hexadecimal characters, enter 0000 or 0 for value. COMMENTS The number of bytes to be unassembled depends on your system display format (40 or 80 columns), and which option you use with the Unassemble command. NOTES: 1. In all cases, the number of bytes unassembled and displayed may be slightly more than either the amount requested or the default amount. This happens because the length of the instructions vary. Therefore, unassembling the last instruction may result in more bytes than expected. 2. Make sure that the address parameters refer to locations containing valid 8086/8088 instruction codes. If you specify an address that does not contain the first byte of a valid instruction, the display will be incorrect. 3. If you enter only an offset for the starting address, the U command assumes the segment contained in the CS register. The Unassemble command has the following two format options: OPTION 1 Use this option to either unassemble instructions without specifying an address, or to unassemble instructions beginning with a specified address. For example: U or U address Sixteen bytes are unassembled with a 40-column display. Thirty-two bytes are unassembled in 80-column mode. Instructions are unassembled beginning with the specified address. If you do not specify an address, the U command assumes the starting address is the location following the last instruction unassembled by a previous U command. Thus, it is possible to unassemble consecutive locations, producing continuous unassembled displays, by entering consecutive U commands without parameters. If no previous U command is entered, the location is offset hex 0100 into the segment originally initialized in the segment registers by DEBUG. OPTION 2 Use this option to unassemble instructions in a specified address range. For example: U range All instructions in the specified address range are unassembled, regardless of the system display format. NOTE: If you specify an ending address, enter it with only an offset value. For example: U 04ba:0100 108 The display response may be: 04BA:0100 206472 AND [SI+72],AH 04BA:0103 FC CLD 04BA:0104 7665 JBE 016B 04BA:0106 207370 AND [BP+DI+70],DH The same display appears if you enter: U 04BA:100 L 7 or U 04BA:100 L 8 or U 04BA:100 L 9 W (WRITE) COMMAND PURPOSE Writes the data being debugged to disk. FORMAT W [address [drive sector sector]] PARAMETERS address Any of the following formats: A segment register plus an offset, such as CS:0100. A segment address plus an offset, such as 4BA:0100. An offset only, such as 100. In this case, the default segment is used. drive A decimal number that indicates a particular drive. For example, drive A is 0, drive B is 1, and so on. sector 1-3 character hexadecimal values that specify the starting relative sector number and the number of sectors to be loaded or written. NOTE: Relative sector numbers are obtained by counting the sectors on the disk surface. The first sector on the disk is at track 0, sector 1, head 0, and is relative sector 0. The numbering continues for each sector on that track and head, then continues with the first sector on the next head of the same track. When all sectors on all heads of the track have been counted, numbering continues with the first sector on head 0 of the next track. COMMENTS No more than hex 80 sectors can be written with a single Write command. A sector contains 512 bytes. DEBUG displays a message if a disk write error occurs. You can retry the write operation by pressing the F3 key to re-display the Write command, then press the Enter key. The Write command has two format options. OPTION 1 Use this option to write data to disk beginning at a specified address. For example: W address drive sector sector The data beginning at the specified address is written to the disk in the indicated drive. The data is written starting at the specified starting relative sector (first sector) and continues until the requested number of sectors are filled (second sector). NOTES: 1. Be extremely careful when you write data to absolute sectors because an erroneous sector specification destroys whatever was on the disk at that location. 2. If only an offset is entered for the beginning address, the W command assumes the segment is contained in the CS register. 3. Remember, the starting sector and the sector count are both specified in hexadecimal. 4. Option 1 cannot be used if the specified drive is a network drive. For example: W 1FD 1 100 A The data beginning at CS:01FD is written to the diskette in drive B, starting at relative sector hex 100 (256) and continuing for hex 0A (10) sectors. OPTION 2 This option permits you to use the WRITE command without specifying parameters or specifying only the address parameter. For example: W or W address When issued as shown above, the Write command writes the file (whose file specification is at CS:80) to disk. This condition is met by specifying the file when starting the DEBUG program, or by using the Name command. NOTE: If DEBUG was started with a file specification and subsequent Name commands were used, you may need to enter a new Name command for the proper file specification before issuing the Write command. In addition, the BX and CX registers must be set to the number of bytes to be written. They may have been set properly by the DEBUG or Load commands, but were changed by a Go or Trace command. You must be certain the BX and CX registers contain the correct values. The file beginning at CS:100, or at the location specified by address, is written to the diskette in the drive included in the file specification or the default drive if no drive was specified. The debugged file is written over the original file that was loaded into memory, or into a new file if the file name in the FCB didn't previously exist. NOTE: An error message is issued if you try to write a file with an extension of .EXE or .HEX. These files are written in a specific format that DEBUG cannot support. If you find it necessary to modify a file with an extension of .EXE or .HEX, and the exact locations to be modified are known, use the following procedure: 1. RENAME the file to an extension other than .EXE or .HEX. 2. Load the file into memory using the DEBUG or Load command. 3. Modify the file as needed in memory, but do not try to execute it with the Go or Trace commands. Unpredictable results would occur. 4. Write the file back using the Write command. 5. RENAME the file to its correct name. XA (EMS ALLOCATE) COMMAND PURPOSE Allocates a specified number of expanded memory pages to a handle. FORMAT XA count COMMENTS The count indicates the number of 16K pages to allocate. If the amount of expanded memory identified by count is available, a message is displayed, indicating that a handle has been created. The XS (EMS Status) command can be used to display the number of expanded memory pages that are available. EXAMPLE To allocate two EMS pages, enter: XA 2 If two pages of memory are available, a message like this is displayed: Handle created = 000E XD (EMS DEALLOCATE) COMMAND PURPOSE Deallocates a handle. FORMAT XD handle COMMENTS The handle identifies the number of the handle to be deallocated. If the number is valid, a message is displayed, indicating the handle has been deallocated. The XS (EMS Status) command can be used to display the handles currently being used. EXAMPLE To deallocate a handle when you have only one allocated, you can enter: XD 000E If the handle deallocation is successful, you receive a message like this: Handle 000E deallocated. XM (EMS MAP) COMMAND PURPOSE Maps an EMS logical page to an EMS physical page from an EMS handle. FORMAT XM lpage ppage handle COMMENTS The lpage specifies the number of the handle's logical page that is to be mapped. The ppage is the number of the physical page to be mapped to. The handle is the EMS allocated label used to reference a group of logical pages. If syntax items are valid, a message is displayed indicating that the logical page has been mapped to the physical page. EXAMPLE To map a logical page to a physical page using handle 0001, you can enter: XM 1 0 1 If the mapping is successful, you receive this message: Logical page 01 mapped to physical page 00. XS (EMS STATUS) COMMAND PURPOSE Displays the status of expanded memory. FORMAT XS COMMENTS The following expanded memory information is displayed: Handle %1 has %2 pages allocated . . . Physical page %1 = Frame segment %2 . . . %1 of a total %2 EMS pages have been allocated %1 of a total %2 EMS handles have been allocated EXAMPLE A line is displayed for each handle allocated with its associated logical page count. DEBUG ERROR MESSAGES The following error messages are produced by the DEBUG utility: ACCESS DENIED The result of attempting to Write (W) to a read-only file. DISK ERROR READING DRIVE %1 An invalid parameter was entered on the Load (L) command or an error occurred on issuing the Load (L) command. DISK ERROR WRITING DRIVE %1 An invalid parameter was entered on the Write (W) command or an error occurred on issuing the Write (W) command. EMS HARDWARE/SOFTWARE FAILURE The result of an EMS command. Tells the user EMS is not functioning properly. EMS NOT INSTALLED The result of an EMS command. Tells user EMS is not installed. &HAT. ERROR Points to the offending operand in an error condition. ERROR IN EXE OR HEX FILE The EXE or HEX file are in error. EXE AND HEX FILES CANNOT BE WRITTEN A file in EXE or HEX format cannot be written to a disk. EXEC FAILURE The execution of the requested file failed. FILE CREATION ERROR The result of attempting to Write (W) to a system or hidden file. FILE NOT FOUND Issued from the Load (L) command when a file is not found for loading. FREE PAGES EXCEEDED The result of an EMS command. Tells the user that the request has exceeded the amount of free EMS pages available. HANDLE NOT FOUND The result of an EMS command. Tells the user an EMS handle was not found. INCORRECT DOS VERSION Incorrect version of DEBUG for the DOS version running. INSUFFICIENT MEMORY Not enough memory to Load (L) the specified file. INSUFFICIENT SPACE ON DISK Out of disk space for a Write (W) command. INVALID DRIVE SPECIFICATION The drive referenced by the Name (N) and Load (L) command is invalid; that is, it does not exist. LOGICAL PAGE OUT OF RANGE The result of an EMS command. Tells the user that the logical page requested is not in the range of possible pages. MISSING OR INVALID EMS PARAMETER The result of an EMS command. Tells the user a missing or invalid parameter was entered. NO FREE HANDLES The result of an EMS command. Tells the user that there are no more EMS handles available for allocation. PARAMETER ERROR The result of an EMS command. Tells the user that an EMS parameter is in error. PHYSICAL PAGE OUT OF RANGE The result of an EMS command. Tells the user that the physical page requested is not in the range of possible pages. PROGRAM TERMINATED NORMALLY An Interrupt 20H has been encountered, signalling program termination. TOTAL PAGES EXCEEDED The result of an EMS command. Tells the user that the total EMS pages have been exceeded. WRITE (W) ERROR, NO DESTINATION DEFINED Attempt to Write (W) to a file that has not yet been Named (N). WRITE PROTECT ERROR WRITING DRIVE %1 A Write (W) to a write-protected disk caused an error. WRITING %1 BYTES Reports the number of bytes written to a file when the Write (W) command is issued.
Chapter 11
CHAPTER 11. WRITING AN INSTALLABLE DEVICE DRIVER 26 Types of Device Drivers 39 Character Device Drivers 48 Block Device Drivers 55 How DOS 4.00 Installs Device Drivers 84 The Basic Parts of a Device Driver 134 The Device Driver Header 148 The Strategy Routine 274 The Interrupt Routines 283 How DOS 4.00 Passes a Request 300 Responding to Requests 392 Initialization Request 456 Media Check Request 511 Build BPB Request 630 Input and Output Requests 815 Nondestructive Input No Wait Request 879 Character Input and Output Status Requests 901 Character Input and Output Flush Requests 935 Open and Close Requests 951 Removable Media Request 983 Generic IOCTL Request 1008 Get Logical Device Request 1037 Set Logical Device Request 1055 CLOCK$ Device Driver Example 1073 CHAPTER 11. WRITING AN INSTALLABLE DEVICE DRIVER This chapter provides guide and system architecture information to support successful creation of an installable device driver. We recommend you use the information provided in this chapter in conjunction with the information provided in the VDISK.ASM file on the utilities diskette. This file contains the fully documented source code for the VDISK device driver, which emulates a fixed disk in RAM. NOTE: The example on the utilities diskette does not reflect the current level of VDISK.SYS.. TYPES OF DEVICE DRIVERS A device driver is a memory image file or an .EXE file that contains the code needed to implement a device. DOS 4.00 allows two types of device drivers to be installed: Character device drivers Block device drivers. CHARACTER DEVICE DRIVERS Character device drivers perform character I/O in a serial manner and have names such as CON, AUX, CLOCK$. You can open handles or FCBs to perform input and output to character devices. Because character device drivers have only one name, they support only one device. BLOCK DEVICE DRIVERS Block device drivers are the fixed disk or diskette drives on the system. They perform random I/O in pieces called blocks, which are usually the physical sector size of the disk. Block devices are not named as character devices are and you cannot open them. Instead they are mapped using the drive letters such as A, B, and C. A single block device driver can be responsible for one or more disk or diskette drives. For example, the first block device driver in the device chain may define four units such as A, B, C, and D. The second device driver may define three units: E, F, and G. The limit is 26 devices with the letters A through Z assigned to drives. The position of the driver in the chain determines the way in which the drive units and drive letters correspond. Support for Media Greater than 32MB A block device driver that runs in the DOS 4.00 environment can be written to process 32-bit sector numbers. This ability provides support for fixed disk media greater than 32MB. This support is described in these sections: "The Device Driver Header" on page 11-3 "Build BPB Request" on page 11-14 "Input and Output Requests" on page 11-18. DOS 4.00 also allows users to install their own device drivers that support media greater than 32MB. HOW DOS 4.00 INSTALLS DEVICE DRIVERS DOS 4.00 installs device drivers dynamically at startup time by reading and processing the DEVICE command in CONFIG.SYS. For example, if you have written a device driver called DRIVER1, include the following command in CONFIG.SYS: device=driver1 The DOS 4.00 device interface links device drivers together in a chain, permitting you to add device drivers for optional devices. Each device must be initialized. The device driver's initialization interrupt routine is called once when the device is installed. The initialization routine returns the location in memory of the ending address of the device driver. After setting the ending address field, a character device driver sets the status word and returns. DOS 4.00 processes installed character device drivers before handling default devices. To have DOS 4.00 install a new CON device (for example, in the device driver header's Name/Unit field) name the device CON and set the standard input device and standard output device bits in the attribute field. Because DOS 4.00 installs drivers anywhere in memory, care must be taken in any references to locations not in the segment. Your driver will not always be loaded at the same memory location each time. Block devices are installed in the same manner as character devices, above. Block devices return additional information such as the number of units. This number identifies the devices' logical names. For example, if the current maximum logical device letter is F at the time of the install call, and the block device driver initialization routine returns three logical units, the logical names of the devices are G, H, and I. The mapping is determined by the position of the driver in the device list and the number of units associated with the device. The number of units returned by INIT overrides the value in the name/unit field of the device header. A block device also returns a pointer to a BIOS parameter block (BPB) array. This is a pointer to an array of n word pointers, where n is the number of units defined. If all the units are the same, the array is able to point to the same BIOS parameter block, thus saving space. The array must be protected below the ending address pointer set by the return. The BPB contains information pertinent to the devices such as the sector size and the number of sectors per allocation unit. The sector size in the BPB cannot be greater than the maximum allowed size set by DOS 4.00 initialization. A block device returns the media descriptor byte passed to devices to report which parameters DOS 4.00 is using for a particular drive unit. THE BASIC PARTS OF A DEVICE DRIVER A device driver is a memory image file or an .EXE file containing the code needed to implement a device. All DOS 4.00 installable device drivers have these things in common: A device driver header, which identifies the device to DOS 4.00 and defines the strategy and interrupt entry points. Since a device driver is simply loaded and does not use a program segment prefix, the device header must be located at physical location 0 of the device driver (ORG 0 or no ORG statement). A strategy routine, which saves a pointer to the Request Header. The interrupt routines, which perform the requested operation. THE DEVICE DRIVER HEADER A device driver requires a device header containing the following: +---------------------------------------------------------------------------+ | FIELD LENGTH | +---------------------------------------------------------------------------+ | Pointer to next device header DWORD | +---------------------------------------------------------------------------+ | Attribute WORD | +---------------------------------------------------------------------------+ | Pointer to device strategy routine WORD | +---------------------------------------------------------------------------+ | Pointer to device interrupt routine WORD | +---------------------------------------------------------------------------+ | Name/unit field 8 BYTES | +---------------------------------------------------------------------------+ Pointer to Next Device Header The device driver header is a pointer to the device header of the next device driver. It is a doubleword field set by DOS 4.00 at the time the device driver is loaded. The first word is an offset and the second word is the segment. If you are loading only one device driver, set the device header field to -1 before loading the device. If you are loading more than one device driver, set the first word of the device header field to the offset of the next device driver's header. Set the device header field of the last device driver to -1. Attribute Field The attribute field identifies the device to DOS 4.00. Bit 15 Bit 15 identifies whether the device is a block device or a character device. If bit 15 is set to 0, this indicates a block device. Setting bit 15 to 1 indicates a character device. Note how the setting of bit 15 affects the interpretation of the setting of the bits below. Bit 14 Bit 14, for both character and block devices, tells DOS 4.00 whether the device driver can handle control strings through IOCtl 44H, AL=2 through AL=5. Set bit 14 to 1 if control strings can be processed. IOCtl subfunctions permit the device driver to interpret the information passed to it, such as setting a baud rate or changing form lengths, without performing standard reads and writes. Set bit 14 to 0 if control strings cannot be processed. DOS 4.00 will return an error if an IOCtl is issued to send or receive control strings and bit 14 is set to 0. Bit 13 Bit 13 is used for both block and character devices. For block devices, set bit 13 to 0 if the media is an IBM format. Set bit 13 to 1 if the media is a non-IBM format. For character devices, set bit 13 to 0 if the driver supports output-until-busy. Set bit 13 to 1 if it does not. With the support of output-until-busy, the device driver will send characters to the device if the device is ready. If the device is not ready, the device driver will immediately return an error. Bit 12 Bit 12 is reserved. Bit 11 Set bit 11 if the device driver can handle removable media. This bit is called the open/close removable media bit. Bits 10 through 7 Bits 10 through 7 are reserved. Bit 6 Bit 6 is the generic IOCtl bit for both character and block device drivers. If this bit is set to 1, the device driver supports generic IOCtl function calls. Setting this bit to 1 also indicates support of the Get/Set Logical Drive function for a block device driver. Bits 5 and 4 Bits 5 and 4 are reserved. Bit 3 Set bit 3 to 1 if the character device is a clock device; set bit 3 to 0 if it is not. Bit 2 Set bit 2 to 1 if the character device is the NUL device; set bit 2 to 0 if it is not. Setting the bit tells DOS 4.00 whether the NUL device is being used. The NUL device cannot be reassigned. Bit 1 If bit 15 is set to 0 for a character device, set bit 1 to 1 to indicate that the character device is the current standard output device. If bit 15 is set to 1 for a block device, set bit 1 to 1 to indicate support for 32-bit sector numbers; otherwise 16-bit sector number support is assumed. Bit 0 Set bit 0 to 1 if the character device is the current standard input device; set bit 0 to 0 if it is not the current standard input device. Pointers to Strategy Routine and Interrupt Routines When DOS 4.00 passes a request to a device driver, it calls the device driver twice. These two fields point to the first and second entry points: the strategy routine and the interrupt routine. The fields are word values, so they must be in the same segment as the device header. Name/Unit Field These 8-byte fields identify a character device by name or a block device by unit. A character device name is left-justified followed by spaces, if necessary. For block devices, although DOS 4.00 automatically fills in this field with the value of number of units returned by INIT call, you may choose to place the number of units in the first place. THE STRATEGY ROUTINE DOS 4.00 calls a device driver at the strategy routine at first, passing in a request packet the information describing what DOS 4.00 wants the device driver to do. The strategy routine does not perform the request but queues the request or saves a pointer to the request packet. THE INTERRUPT ROUTINES DOS 4.00 calls the device driver's interrupt routine with no parameters immediately after the strategy routine returns. An interrupt routine's function is to perform the operation based on the queued request, process any data in the request packet, and set up information being returned to DOS 4.00. It is the responsibility of the device driver to preserve the system state. For example, the device driver must save all registers on entry and restore them on exit. The stack maintained by DOS 4.00 is used to save all registers. If more stack space is needed, it is the device driver's responsibility to allocate and maintain an additional stack. All calls to device drivers are FAR calls. FAR returns should be executed to return to DOS 4.00. HOW DOS 4.00 PASSES A REQUEST DOS 4.00 passes a pointer in ES:BX to the request packet. The packet consists of a request header that contains information common to all requests, followed by data pertinent to the request being made. The structure of the request header is shown below. +---------------------------------------------------------------------------+ | FIELD LENGTH | +---------------------------------------------------------------------------+ | Length of the request header and subsequent data BYTE | +---------------------------------------------------------------------------+ | Unit code for block devices only BYTE | +---------------------------------------------------------------------------+ | Command code BYTE | +---------------------------------------------------------------------------+ | Status WORD | +---------------------------------------------------------------------------+ | Reserved 8-BYTE | +---------------------------------------------------------------------------+ | Data VARIABLE | +---------------------------------------------------------------------------+ Length Field The length field identifies the length of the request header and subsequent data in bytes. Unit Code Field The unit code field identifies the requesting unit in a block device driver. If a block device driver has three units defined, for example, the possible values for the unit code field are 0, 1, or 2. Command Code Field The command code identifies the request. See "Responding to Requests" on page 11-8 for a list of command code values and request descriptions. Status Field The status word field is zero on entry and is set by the driver interrupt routine on return. Bit 15 Bit 15 is the error bit. If bit 15 is set to 1, the low order 8 bits of the status word (7-0) indicate the error code. Bits 14 - 10 Bits 14 through 10 are reserved. Bit 9 Bit 9 is the busy bit. As a response to status request call, character device drivers can set the busy bit to indicate whether or not a device is ready to perform input and output requests. Block device drivers can set the busy bit to indicate removable or nonremovable media. See "Character Input and Output Status Requests" on page 11-21 and "Removable Media Request" on page 11-23 for more information about the calls. Bit 8 Bit 8 is the done bit. If set, the operation is complete. The driver sets the done bit to 1 when it exits. Bits 7 - 0 Bits 7 through 0 are the low order 8 bits of the status word. If bit 15 is set, bits 7 through 0 contain the error codes. The error codes and errors are: CODES MEANING 00 Write protect violation 01 Unknown unit 02 Device not ready 03 Unknown command 04 CRC error 05 Bad drive request structure length 06 Seek error 07 Unknown media 08 Sector not found 09 Printer out of paper 0A Write fault 0B Read fault 0C General failure 0D Reserved 0E Reserved 0F Invalid disk change RESPONDING TO REQUESTS Each request packet that is passed to the device driver contains a command code value in the request header to tell the driver which function to perform. The table below contains the DOS 4.00 device interface command code values and the functions to be performed when these values are passed with data. Note that some of these functions are specific to either a block device or a character device. Following this table are detailed descriptions of request data structures and what the interrupt routines are expected to do. Some of these descriptions pertain to more than one command code. +---------------------------------------------------------------------------+ | COMMAND REQUEST DEVICE | | CODE DESCRIPTION TYPE | +---------------------------------------------------------------------------+ | 0 Initialization Both | +---------------------------------------------------------------------------+ | 1 Media check Block | +---------------------------------------------------------------------------+ | 2 Build BPB Block | +---------------------------------------------------------------------------+ | 3 IOCtl input (called only if bit 14 of attribute is Both | | set to 1) | +---------------------------------------------------------------------------+ | 4 Input (read) Both | +---------------------------------------------------------------------------+ | 5 Nondestructive input no wait Character | +---------------------------------------------------------------------------+ | 6 Input status Character | +---------------------------------------------------------------------------+ | 7 Input flush Character | +---------------------------------------------------------------------------+ | 8 Output (write) Both | +---------------------------------------------------------------------------+ | 9 Output (write with verify) Block | +---------------------------------------------------------------------------+ | 10 Output status Character | +---------------------------------------------------------------------------+ | 11 Output flush Character | +---------------------------------------------------------------------------+ | 12 IOCtl output (called only if bit 14 of attribute is Both | | set to 1 | +---------------------------------------------------------------------------+ | 13 Device open (called only if bit 11 of attribute is Both | | set to 1) | +---------------------------------------------------------------------------+ | 14 Device close (called only if bit 11 of attribute is Both | | set to 1) | +---------------------------------------------------------------------------+ | 15 Removable media (called only if bit 11 of attribute Block | | is set to 1) | +---------------------------------------------------------------------------+ | 19 Generic IOCtl Request (called Both | | only if bit 6 of attribute is set to 1) | +---------------------------------------------------------------------------+ | 23 Get logical device (called only if bit 6 of Block | | attribute is set to 1) | +---------------------------------------------------------------------------+ | 24 Set logical device (called only if bit 6 of Block | | attribute is set to 1) | +---------------------------------------------------------------------------+ INITIALIZATION REQUEST COMMAND CODE = 0 +---------------------------------------------------------------------------+ | FIELD LENGTH | +---------------------------------------------------------------------------+ | Request header 13-BYTE | +---------------------------------------------------------------------------+ | Number of units (not set by character devices) BYTE | +---------------------------------------------------------------------------+ | Ending address of resident program code DWORD | +---------------------------------------------------------------------------+ | Pointer to BPB array (not set by character devices) pointer DWORD | | to remainder of arguments | +---------------------------------------------------------------------------+ | Drive number BYTE | +---------------------------------------------------------------------------+ | CONFIG.SYS Error Message control flag WORD | +---------------------------------------------------------------------------+ The driver must do the following: Set the number of units (block devices only). Set up the pointer to the BPB array (block devices only). Perform any initialization code (to modems, printers, and others). Set the ending address of the resident program code. Set the status word in the request header. To obtain information passed from CONFIG.SYS to a device driver at initialization time, the BPB pointer field points to a buffer containing the information passed in CONFIG.SYS following the =. This string may end with either a carriage return (0DH) or a linefeed (0AH). This information is read-only. Only system calls 01H-0CH and 30H can be issued by the initialization code of the driver. The last byte parameter contains the drive letter for the first unit of a block driver. For example, 0=A, 1=B and so forth. If an initialization routine determines that it cannot set up the device and wants to terminate without using any memory, use the following procedure: Set the number of units to 0. Set the ending address offset to 0. Set the ending address segment to the code segment (CS). If there are multiple device drivers in a single memory image file, the ending address returned by the last initialization called is the one DOS 4.00 uses. IBM recommends that all device drivers in a single memory image file return the same ending address. If initialization of your device driver fails, and you want the system to display the ERROR IN CONFIG.SYS LINE # error message, set the CONFIG.SYS error message control flag to a non-zero value. MEDIA CHECK REQUEST COMMAND CODE = 1 +---------------------------------------------------------------------------+ | FIELD LENGTH | +---------------------------------------------------------------------------+ | Request header 13-BYTE | +---------------------------------------------------------------------------+ | Media descriptor from DOS 4.00 BYTE | +---------------------------------------------------------------------------+ | Return BYTE | +---------------------------------------------------------------------------+ | A pointer to the previous volume ID (if bit 11 = 1 and disk DWORD | | change is returned) | +---------------------------------------------------------------------------+ When the command code field is 1, DOS 4.00 calls Media Check for a drive unit and passes its current Media Descriptor byte. See "Media Descriptor Byte." Media Check returns one of the following: Media not changed Media changed Not sure Error code. The driver must perform the following: Set the status word in the request header. Set the return byte to: -1 for "media changed" 0 for "not sure" 1 for "media not changed." The driver uses the following method to determine how to set the return byte: If the media is nonremovable (a fixed disk), set the return byte to 1. If less than 2 seconds since last successful access, set the return byte to 1. If changeline not available, set the return byte to 0. If changeline is available but not active, set the return byte to 1. If the media byte in the new BPB does not match the old media byte, set the return byte to -1. If the current volume ID matches the previous volume ID, or if the serial number matches the previous serial number, set the return byte to 0. Media Descriptor Byte Currently the media descriptor byte has been defined for some media types. This byte should be identical to the media byte if the device has the non-IBM format bit off. These predefined values are: Media descriptor byte --> 1 1 1 1 1 x x x bits --> 7 6 5 4 3 2 1 0 BIT MEANING 0 1=2-sided 0=not 2-sided 1 1=8 sector 0=not 8 sector 2 1=removable 0=not removable 3-7 must be set to 1 NOTE: An exception to the above is that the media descriptor byte value of F0, which is used to indicate any media types not defined, and F9, which is used for 5.25-inch media with 2 sides and 15 sectors/tracks. Examples of current DOS 4.00 media descriptor bytes: +---------------------------------------------------------------------------+ | DISK # SECTORS/ MEDIA | | TYPE SIDES TRACK DESCRIPTOR | +---------------------------------------------------------------------------+ | Fixed disk -- -- F8H | +---------------------------------------------------------------------------+ | 5.25 inch 2 15 F9H | +---------------------------------------------------------------------------+ | 5.25 inch 1 9 FCH | +---------------------------------------------------------------------------+ | 5.25 inch 2 9 FDH | +---------------------------------------------------------------------------+ | 5.25 inch 1 8 FEH | +---------------------------------------------------------------------------+ | 5.25 inch 2 8 FFH | +---------------------------------------------------------------------------+ | 8 inch 1 26 FEH | +---------------------------------------------------------------------------+ | 8 inch 2 26 FDH | +---------------------------------------------------------------------------+ | 8 inch 2 8 FEH | +---------------------------------------------------------------------------+ | 3.5 inch 2 9 F9H | +---------------------------------------------------------------------------+ | 3.5 inch 2 18 F0H | +---------------------------------------------------------------------------+ To determine whether you are using a single-sided or a double-sided diskette, attempt to read the second side. If an error occurs, you may assume the diskette is single-sided. Media descriptor F0H may be used for those media types not described earlier. Programs should not use the media descriptor values to distinguish media. DOS 4.00 internal routines use information in the BIOS parameter block (BPB) to determine the media type of IBM-formatted diskettes. These media descriptor bytes do not necessarily indicate a unique media type. For 8-inch diskettes: FEH (IBM 3740 Format) -- Single-sided, single-density, 128 bytes per sector, soft-sectored, 4 sectors per allocation unit, 1 reserved sector, 2 FATs, 68 directory entries, 77*26 sectors. FDH (IBM 3740 Format) -- Double-sided, single-density, 128 bytes per sector, soft-sectored, 4 sectors per allocation unit, 4 reserved sectors, 2 FATs, 68 directory entries, 77*26*2 sectors. FEH -- Double-sided, double-density, 1024 bytes per sector, soft sectored, 1 sector per allocation unit, 1 reserved sector, 2 FATs, 192 directory entries, 77*8*2 sectors. BUILD BPB REQUEST COMMAND CODE = 2 +---------------------------------------------------------------------------+ | FIELD LENGTH | +---------------------------------------------------------------------------+ | Request header 13-BYTE | +---------------------------------------------------------------------------+ | Media descriptor from DOS 4.00 BYTE | +---------------------------------------------------------------------------+ | Transfer address (buffer address) DWORD | +---------------------------------------------------------------------------+ | Pointer to BPB table DWORD | +---------------------------------------------------------------------------+ DOS 4.00 calls Build BPB (BIOS Parameter Block) under the following two conditions: If "Media Changed" is returned If "Not Sure" is returned, there are no used buffers. Used buffers are buffers with changed data not yet written to the disk. The driver must do the following: Set the pointer to the BPB Set the status word in the request header. The device driver must determine the media type that is in the unit to return the pointer to the BPB table. In previous versions of IBMBIO, the FAT ID byte determined the structure and layout of the media. The FAT ID byte has only eight possible values (F8 through FF), so, as new media types are invented, the available values will soon be exhausted. With the varying media layouts, DOS 4.00 needs to be aware of the location of the FATs and directories before it asks to read them. The following paragraphs explain the method DOS 4.00 uses to determine the media type. The information relating to the BPB for a particular media is kept in the boot sector for the media. The format of the boot sector is as follows: +---------------------------------------------------------------------------+ | FIELD LENGTH | +---------------------------------------------------------------------------+ | A 2-byte short JMP instruction (EBH), followed by a NOP WORD | | instruction (90H). | +---------------------------------------------------------------------------+ | Product name and version 8 BYTES | +---------------------------------------------------------------------------+ | Bytes per sector; must be power of 2 WORD | +---------------------------------------------------------------------------+ | Sectors per allocation unit; must be power of 2 BYTE | +---------------------------------------------------------------------------+ +---------------------------------------------------------------------------+ | FIELD LENGTH | +---------------------------------------------------------------------------+ | Reserved sectors starting at logical sector 0 WORD | +---------------------------------------------------------------------------+ | Number of FATs BYTE | +---------------------------------------------------------------------------+ | Maximum number of root directory entries WORD | +---------------------------------------------------------------------------+ | Total number of sectors in media including the boot sector, WORD | | FAT areas, and directories | +---------------------------------------------------------------------------+ | Media descriptor BYTE | +---------------------------------------------------------------------------+ | Number of sectors occupied by a FAT WORD | +---------------------------------------------------------------------------+ | Sectors per track WORD | +---------------------------------------------------------------------------+ | Number of heads WORD | +---------------------------------------------------------------------------+ | Number of hidden sectors WORD | +---------------------------------------------------------------------------+ The BPB information contained in the boot sector starts with the Bytes per Sector entry. The last three words are intended to help the device driver identify the media. The number of heads is useful for supporting different multihead drives with the same storage capacity but a different number of surfaces. The number of hidden sectors is useful for supporting drive partitioning schemes. For drivers that support volume identification and disk change, this call causes a new volume identification to be read from the disk. This call indicates that the disk has changed in a permissible manner. To handle the partition that is bigger than 32MB, or one that starts beyond or crosses the 32MB boundary, DOS 4.00 defines an extended BPB structure. Depending on the size of the media, you can use either the existing BPB or the extended one, which contains an additional DWORD field to indicate the size of the partition in sectors. Bit 1 of the attribute field in the block device driver header indicates whether the device can process 32-bit sector numbers. Set bit 1 to indicate 32-bit support. +---------------------------------------------------------------------------+ | FIELD LENGTH | +---------------------------------------------------------------------------+ | Bytes per sector WORD | +---------------------------------------------------------------------------+ | Sectors per allocation unit BYTE | +---------------------------------------------------------------------------+ | Reserved sectors starting at logical sector 0 WORD | +---------------------------------------------------------------------------+ +---------------------------------------------------------------------------+ | FIELD LENGTH | +---------------------------------------------------------------------------+ | Number of FATs -- 0 if not a FAT system BYTE | +---------------------------------------------------------------------------+ | Maximum number of root directory entries WORD | +---------------------------------------------------------------------------+ | Total number of sectors in the media. This field is used to WORD | | define a partition that is less than 32MB. Setting this | | field to 0 indicates to use the total (32-bit) number of | | sectors in the media below. | +---------------------------------------------------------------------------+ | Media descriptor BYTE | +---------------------------------------------------------------------------+ | Number of sectors occupied by a FAT WORD | +---------------------------------------------------------------------------+ | Sectors per track WORD | +---------------------------------------------------------------------------+ | Number of heads WORD | +---------------------------------------------------------------------------+ | Number of hidden sectors DWORD | +---------------------------------------------------------------------------+ | Total (32-bit) number of sectors in the media. This field is DWORD | | used to define a partition that is greater than 32MB, or one | | that crosses the 32MB boundary. | +---------------------------------------------------------------------------+ The extended BPB is a superset of the traditional BPB structure. To achieve the maximum compatibility between this structure and that of the traditional BPB, DOS 4.00 uses the following rule: If (the number of hidden sectors plus the total number of sectors in the media) is greater than 64KB, use the 32-bit total number of sectors in the media entry (DWORD). Otherwise, use the TOTAL NUMBER OF SECTORS IN THE MEDIA entry (WORD). A boot record exists at the beginning of each disk partition and each extended DOS 4.00 partition volume. DOS 4.00 automatically creates the extended boot record. The format of the extended boot record is: +---------------------------------------------------------------------------+ | FIELD LENGTH | +---------------------------------------------------------------------------+ | A 2-byte short JMP instruction (EBH) followed by a NOP WORD | | instruction (90H). | +---------------------------------------------------------------------------+ | Product name and version 8 BYTES | +---------------------------------------------------------------------------+ | Extended BPB 25 BYTES | +---------------------------------------------------------------------------+ | Physical drive number BYTE | +---------------------------------------------------------------------------+ | Reserved BYTE | +---------------------------------------------------------------------------+ | Extended boot record signature BYTE | +---------------------------------------------------------------------------+ | Volume serial number DWORD | +---------------------------------------------------------------------------+ | Volume label 11 BYTES | +---------------------------------------------------------------------------+ | Reserved 8 BYTES | +---------------------------------------------------------------------------+ NOTE: The value of Extended boot record signature is 29H. The value of the physical drive number is always 0H or 80H. On all requests to extended drivers with a sector number in their request headers, the sector number is a DWORD. The standard DOS 4.00 block device drivers set the attribute bit 1 for 32-bit support. For each call to a device driver, DOS 4.00 checks to see if the starting sector number passed in the request can be supported by the device driver. If this value is greater than 64K for an old-style device driver, DOS 4.00 returns an UNKNOWN MEDIA (07H) device driver error. INPUT AND OUTPUT REQUESTS COMMAND CODES = 3, 4, 8, 9, 12 +---------------------------------------------------------------------------+ | FIELD LENGTH | +---------------------------------------------------------------------------+ | Request header 13-BYTE | +---------------------------------------------------------------------------+ | Media descriptor byte BYTE | +---------------------------------------------------------------------------+ | Transfer address (buffer address) DWORD | +---------------------------------------------------------------------------+ | Byte/sector count WORD | +---------------------------------------------------------------------------+ | Starting sector number (If -1, use DWORD starting sector WORD | | number. This entry has no meaning for a character device.) | +---------------------------------------------------------------------------+ | For DOS 3.0 to DOS 4.00, pointer to the volume identification DWORD | | if error code 0FH is returned | +---------------------------------------------------------------------------+ | Starting 32-bit sector number. (Use this entry to the block DWORD | | device driver with the attribute bit 1 set.) | +---------------------------------------------------------------------------+ The DOS 4.00 INPUT/OUTPUT request structure can process 32-bit sector numbers, providing support for media of more than 4 billion sectors. The driver must do the following: Set the status word in the request header Perform the requested function Set the actual number of sectors or bytes transferred. No error checking is performed on an IOCtl call. However, the driver must set the return sector or byte count to the actual number of bytes transferred. Under certain circumstances the block device driver may be asked to do a WRITE operation of 64KB that seems to be a wraparound of the transfer address in the device driver request packet. This occurs because an optimization is added to the WRITE code in DOS 4.00. It will only happen on WRITEs that are within a sector size of 64KB on files that are being extended past the current end of file. The block device driver is allowed to ignore the balance of the WRITE that wraps around. For example, a WRITE of 10000H bytes of sectors with a transfer address of XXXX:1 ignores the last two bytes. Remember that a program using DOS 4.00 function calls cannot request an input or output operation of more than FFFFH bytes because a wrap around in the transfer buffer segment must occur. You can ignore bytes that would have wrapped around in the transfer segment. If the driver returns an error code of 0FH (Invalid Disk Change), it must provide a DWORD pointer to an ASCIIZ string identifying the correct volume ID and the system prompts the user to reinsert the disk. The reference count of open files on the disk maintained by OPEN and CLOSE calls allows the driver to determine when to return error 0FH. If there are no open files (reference count=0) and the disk has been changed, the I/O is valid, and error 0FH is not returned. If there are open files (reference count > 0) and the disk has been changed, an error 0FH situation may exist. DOS 4.00 IBMDOS.COM will request an OPEN or CLOSE function only if SHARE is loaded. NONDESTRUCTIVE INPUT NO WAIT REQUEST COMMAND CODE = 5 +---------------------------------------------------------------------------+ | FIELD LENGTH | +---------------------------------------------------------------------------+ | Request header 13-BYTE | +---------------------------------------------------------------------------+ | Byte read from device BYTE | +---------------------------------------------------------------------------+ The driver must do the following: Return a byte from the device. Set the status word in the request header. If the character device returns busy bit = 0, meaning there are characters in buffer, the next character that would be read is returned. This character is not removed from the input buffer, (that is, nondestructive input). This call allows DOS 4.00 to look ahead one input character. CHARACTER INPUT AND OUTPUT STATUS REQUESTS COMMAND CODES = 6, 10 +---------------------------------------------------------------------------+ | FIELD LENGTH | +---------------------------------------------------------------------------+ | Request header 13-BYTE | +---------------------------------------------------------------------------+ The driver must do the following: Perform the requested function. Set the busy bit. Set the status word in the request header. The busy bit is set differently for output and input. Output on Character Devices If the busy bit is 1 on return, a write request would wait for completion of a current request. If the busy bit is 0, no request is waiting or running. Therefore, a write request would start immediately. Input on Character Devices with a Buffer If the busy bit is 1 on return, a read request goes to the physical device. If the busy bit is 0, characters are in the device buffer and a read returns quickly. This also indicates that the user has typed something. DOS 4.00 assumes that all character devices have a type-ahead input buffer. Devices that do not have this buffer should always return busy = 0 so that DOS 4.00 does not loop endlessly, waiting for information to be put in a buffer that does not exist. CHARACTER INPUT AND OUTPUT FLUSH REQUESTS COMMAND CODES = 7, 11 +---------------------------------------------------------------------------+ | FIELD LENGTH | +---------------------------------------------------------------------------+ | Request header 13-BYTE | +---------------------------------------------------------------------------+ This call tells the driver to flush (terminate) all pending requests of which it has knowledge. Its primary use is to flush the input queue on character devices. The driver must set the status word in the Request Header upon return. OPEN AND CLOSE REQUESTS COMMAND CODES = 13, 14 +---------------------------------------------------------------------------+ | FIELD LENGTH | +---------------------------------------------------------------------------+ | Request header 13-BYTE | +---------------------------------------------------------------------------+ These calls are designed to give the device information about current file activity on the device if bit 11 of the attribute word is set. On block devices, these calls can be used to manage local buffering. The device can keep a reference count. Every OPEN increases the reference count. Every CLOSE decreases the device reference count. When the reference count is 0, there are no open files on the device. Therefore, the device should flush buffers inside the device to which it has written because the user can change the media on a removable media drive. If the media has been changed, reset the reference count to 0 without flushing the buffers. These calls are more useful on character devices. The OPEN call can send a device an initialization string. On a printer, the call can send a string to set the font or the page size so the printer is always in a known state at the start of an I/O stream. Similarly, the CLOSE call can send a post string, such as a form feed, at the end of an I/O stream. Using IOCtl to set the preliminary and ending strings provides a flexible mechanism for serial I/O device stream control. REMOVABLE MEDIA REQUEST COMMAND CODE = 15 +---------------------------------------------------------------------------+ | FIELD LENGTH | +---------------------------------------------------------------------------+ | Request header 13-BYTE | +---------------------------------------------------------------------------+ To use this call, set bit 11 of the attribute field to 1. Block devices can use this call only by way of a subfunction of the IOCtl function call (44H). This call is useful because it notifies a utility if it is dealing with a removable or nonremovable media drive. For example, the FORMAT utility needs to know whether a drive is removable or nonremovable because it displays different versions of some prompts. The information is returned in the busy bit of the status word. If the busy bit is 1, the media is nonremovable. If the busy bit is 0, the media is removable. No error bit checking is performed. It is assumed that this call always succeeds. GENERIC IOCTL REQUEST COMMAND CODE = 19 +---------------------------------------------------------------------------+ | FIELD LENGTH | +---------------------------------------------------------------------------+ | Request header 13-BYTE | +---------------------------------------------------------------------------+ | Major function BYTE | +---------------------------------------------------------------------------+ | Minor function BYTE | +---------------------------------------------------------------------------+ | Contents of SI WORD | +---------------------------------------------------------------------------+ | Contents of DI WORD | +---------------------------------------------------------------------------+ | Pointer to Generic IOCTL request packet DWORD | +---------------------------------------------------------------------------+ The driver must: Support the functions described under Generic IOCtl request Maintain its own track table (TrackLayout). See Appendix C, "I/O Control for Devices (IOCtl)" on page C-1 for a description of the functions provided by generic IOCtl requests. GET LOGICAL DEVICE REQUEST COMMAND CODE = 23 +---------------------------------------------------------------------------+ | FIELD LENGTH | +---------------------------------------------------------------------------+ | Request header 13-BYTE | +---------------------------------------------------------------------------+ | Input (unit code) BYTE | +---------------------------------------------------------------------------+ | Command code BYTE | +---------------------------------------------------------------------------+ | Status WORD | +---------------------------------------------------------------------------+ | Reserved DWORD | +---------------------------------------------------------------------------+ SET LOGICAL DEVICE REQUEST COMMAND CODE = 24 +---------------------------------------------------------------------------+ | FIELD LENGTH | +---------------------------------------------------------------------------+ | Request header 13-BYTE | +---------------------------------------------------------------------------+ | Input (unit code) BYTE | +---------------------------------------------------------------------------+ | Command code BYTE | +---------------------------------------------------------------------------+ | Status WORD | +---------------------------------------------------------------------------+ | Reserved DWORD | +---------------------------------------------------------------------------+ CLOCK$ DEVICE DRIVER EXAMPLE This feature is a "Real-Time Clock" Board. To allow this board to be integrated into the system for TIME and DATE, a special device driver is specified by an attribute word, the CLOCK$ device. This device driver defines and performs functions like any other character device driver. Most functions will be set done bit, reset error bit, return. When a read or write to this device occurs, 6 bytes are transferred. The first 2 bytes are a word, which is the count of days since 1-1-80. The third byte is minutes; the fourth is hours; the fifth is hundredths of seconds; and the sixth is seconds. Reading the CLOCK$ device gets the date and time; writing to it sets the date and time. PART 3. APPENDIXES
Appendix A
APPENDIX A. DOS 4.00 INTERRUPTS 13 20H Program Terminate 21 21H Function Request 41 22H Terminate Address 46 23H Ctrl-Break Exit Address 53 24H Critical Error Handler Vector 83 25H/26H Absolute Disk Read/Write 287 27H Terminate but Stay Resident 353 28H-2EH Reserved for DOS 4.00 392 2FH Multiplex Interrupt 396 30H-3FH Reserved for DOS 4.00 695
APPENDIX A. DOS 4.00 INTERRUPTS
This chapter contains information to support use of the DOS 4.00 interrupts.
DOS 4.00 reserves interrupt types 20H to 3FH for its use. Absolute memory locations 80H to FFH are reserved by DOS 4.00. All interrupt values are in hexadecimal.
20H PROGRAM TERMINATE
Issue interrupt 20H to exit from a program. This vector transfers to the logic in DOS 4.00 to restore the terminate address, the Ctrl-Break address, and the critical error exit address to the values they had on entry to the program. All file buffers are flushed and all handles are closed. You should close all files changed in length (see function call 10H and 3EH) before issuing this interrupt. If the changed file is not closed, its length, date, and time are not recorded correctly in the directory.
For a program to pass a completion code or an error code when terminating, it must use either function call 4CH (Terminate a Process) or 31H (Terminate Process and Stay Resident). These two methods are preferred over using interrupt 20H, and the codes returned by them can be interrogated in batch processing. See function call 4CH for information on the ERRORLEVEL subcommand of batch processing.
IMPORTANT: Before you issue interrupt 20H, your program must ensure that the CS register contains the segment address of its program segment prefix.
21H FUNCTION REQUEST
Refer to each function call issued within 21H in Appendix B, "DOS 4.00 Function Calls" on page B-1.
22H TERMINATE ADDRESS
Control transfers to the address at this interrupt location when the program terminates. This address is copied into the program's Program Segment Prefix at the time the segment is created. You should not issue this interrupt; the EXEC function call does this for you.
23H CTRL-BREAK EXIT ADDRESS
If the user presses the Ctrl and Break keys during standard input, standard output, standard printer, or asynchronous communications adapter operations, an interrupt 23H is executed. If BREAK is on, the interrupt 23H is checked on most function calls (except calls 06H and 07H). If the user-written Ctrl-Break routine saves all registers, it may end with a return-from-interrupt instruction (IRET) to continue program execution.
If the user-written interrupt program returns with a long return, the carry flag is used to determine whether the program will be ended. If the carry flag is set, the program is ended, otherwise execution continues (as with a return by IRET).
If the user-written Ctrl-Break interrupt uses function calls 09H or 0AH, then &hat.C, carriage-return and linefeed are output. If execution is continued with an IRET, I/O continues from the start of the line.
When the interrupt occurs, all registers are set to the value they had when the original function call to DOS 4.00 was made. There are no restrictions on what the Ctrl-Break handler is allowed to do, including DOS 4.00 function calls, as long as the registers are unchanged if IRET is used.
When the program creates a new segment and loads in a second program it changes the Ctrl-Break address. The termination of the second program and return to the first causes the Ctrl-Break address to be restored to the value it had before execution of the second program. It is restored from the second program's Program Segment Prefix. You should not issue this interrupt.
24H CRITICAL ERROR HANDLER VECTOR
A critical error is returned when a DOS function cannot be performed. This error is frequently caused by a hardware condition, such as the printer being out of paper, a diskette drive door open, or a diskette out of space. When a critical error occurs within DOS 4.00, control is transferred with an interrupt 24H. On entry to the error handler, AH will have its bit 7=0 (high-order bit) if the error was a disk error (the most common occurrence), bit 7=1 if it was not.
BP:SI contains the address of a Device Header Control Block from which additional information can be retrieved. See page A-5.
The registers are set up for a retry operation, and an error code is in the lower half of the DI register with the upper half undefined. The error codes follow:
ERROR CODE MEANING 0 Attempt to write on write-protected diskette 1 Unknown unit 2 Drive not ready 3 Unknown command 4 Data error (CRC) 5 Bad request structure length 6 Seek error 7 Unknown media type 8 Sector not found 9 Printer out of paper A Write fault B Read fault C General failure
The user stack is in effect and contains the following from top to bottom:
IP DOS 4.00 registers from issuing INT 24H
CS FLAGS AX User registers at time of original BX INT 21H request CX DX SI DI BP DS ES IP From the original interrupt 21H CS from the user to DOS 4.00 FLAGS
The registers are set such that if an IRET is executed, DOS 4.00 responds according to (AL) as follows:
(AL) =0 ignore the error. =1 retry the operation. =2 terminate the program through interrupt 22H. =3 fail the system call in progress.
NOTE: Be careful when choosing ignore as a response because this causes DOS 4.00 to believe that an operation has completed successfully when it may not have.
To return control from the critical error handler to a user error routine, the following should occur:
Before an INT 24H occurs:
1. The user application initialization code should save the INT 24H vector and replace the vector with one pointing to the user error routine.
When the INT 24H occurs:
2. When the user error routine receives control, it should push the flag register onto the stack, and then execute a CALL FAR to the original INT 24H vector saved in step 1.
3. DOS 4.00 gives the appropriate prompt, and waits for the user input (Abort, Retry, Fail or Ignore). After the user input, DOS 4.00 returns control to the user error routine at the instruction following the CALL FAR.
4. The user error routine can now do any tasks necessary. To return to the original application at the point the error occurred, the error routine needs to execute an IRET instruction. Otherwise, the user error routine should remove the IP, CS, and Flag registers from the stack. Control can then be passed to the desired point.
Disk Errors
If it is a hard error on disk (AH bit 7=0), register AL contains the failing drive number (0 = drive A, and so on). AH bits 0-2 indicate the affected disk area and whether it was a read or write operation, as follows:
Bit 0=0 if read operation, 1 if write operation Bits 2-1 (affected disk area) 0 0 DOS 4.00 area 0 1 file allocation table 1 0 directory 1 1 data area
AH bits 3-5 indicate which responses are valid. They are:
Bit 3=0 if FAIL is not allowed =1 if FAIL is allowed Bit 4=0 if RETRY is not allowed =1 if RETRY is allowed Bit 5=0 if IGNORE is not allowed =1 if IGNORE is allowed
Handling of Invalid Responses
If IGNORE is specified (AL=0) and IGNORE is not allowed (bit 5=0), make the response FAIL (AL=3).
If RETRY is specified (AL=1) and RETRY is not allowed (bit 4=0), make the response FAIL (AL=3).
If FAIL is specified (AL=3) and FAIL is not allowed (bit 3=0), make the response END (AL=2).
Other Errors
If AH bit 7=1, the error occurred on a character device, or was the result of a bad memory image of the FAT. The device header passed in BP:SI can be examined to determine which case exists. If the attribute byte high-order bit indicates a block device, then the error was a bad FAT. Otherwise, the error is on a character device.
If a character device is involved, the contents of AL are unpredictable and the error code is in DI as above.
NOTES:
1. Retry five times before giving this routine control for disk errors. When the errors are in the FAT or a directory, retry three times.
2. For disk errors, this exit is taken only for errors occurring during an interrupt 21H function call. It is not used for errors during an interrupt 25H or 26H.
3. This routine is entered in a disabled state.
4. All registers must be preserved.
5. This interrupt handler should refrain from using DOS 4.00 function calls. If necessary, it may use calls 01H through 0CH, 30H, and 59H. Use of any other call destroys the DOS 4.00 stack and leaves DOS 4.00 in an unpredictable state.
6. The interrupt handler must not change the contents of the device header.
7. If the interrupt handler handles errors itself rather than returning to DOS 4.00, it should restore the application program's registers from the stack, remove all but the last three words on the stack, then issue an IRET. This will return to the program immediately after the INT 21H that experienced the error. Note that if this is done, DOS 4.00 will be in an unstable state until a function call higher than 0CH is issued; therefore, it is not recommended.
The recommended way to end a critical error is to use FAIL and then test the extended error code of the INT 21H.
8. IGNORE requests (AL=0) are converted to FAIL for critical errors that occur on FAT or DIR sectors.
9. Refer to "Responding to Errors" on page B-5 and "Extended Error Codes" on page B-5 for information on how to obtain additional error information.
10. For DOS 4.00, IGNORE requests (AL=0) are converted to FAIL requests for certain critical errors (50-79).
The device header pointed to by BP:SI is formatted as follows:
+---------------------------------------------------------------------------+ | DWORD Pointer to next device (FFFFH if last device) | +---------------------------------------------------------------------------+ | WORD Attributes: | | Bit 15 = 1 if character device | | = 0 if block device | | If bit 15 is 1: | | Bit 0 = 1 if current standard input | | Bit 1 = 1 if current standard output | | Bit 2 = 1 if current NULL device | | Bit 3 = 1 if current CLOCK device | | Bit 14 is the IOCtl bit | +---------------------------------------------------------------------------+ | WORD pointer to device driver strategy entry point. | +---------------------------------------------------------------------------+ | WORD pointer to device driver interrupt entry point. | +---------------------------------------------------------------------------+ | 8-BYTE character device named field for block devices. The first byte is | | the number of units. | +---------------------------------------------------------------------------+
To tell if the error occurred on a block or character device, look at bit 15 in the attribute field (WORD at BP:SI+4).
If the name of the character device is desired, look at the eight bytes starting at BP:SI+10.
25H/26H ABSOLUTE DISK READ/WRITE
Interrupt vectors 25H and 26H transfer control to the device driver. They have been extended to allow direct access to media greater than 32MB in size. Their use of the CX register is what distinguishes them from the conventional 25H and 26H interrupts. Note that if the conventional format parameters are used in an attempt to access media greater than 32MB, an error code of 0207H is returned in AX.
The request for extended 25H or 26H is:
MOV AL,DRIVE ; Drive number to process
- 0 = A
- 1 = B
- 2 = C . . .
LDS BX,PACKET ; Parameter list MOV CX,-1 ; Indicates extended format INT 25H or 26H ; Issue request to DOS 4.00 POP AX ; Discard stack word JC ERROR ; Error code returned in AX
PACKET LABEL BYTE ; Control packet DD RBA ; RBA of first sector
- (0 origin)
DW COUNT ; Number of sectors to I/O DD BUFFER ; Data buffer
On return, the original flags are still on the stack (put there by the INT instruction). This is necessary because return information is passed back in the current flags. Be sure to pop the stack to prevent uncontrolled growth.
WARNING: IF DISK I/O HANDLED BY THIS INTERRUPT EXCEEDS THE LIMIT IMPOSED BY THE 64KB DIRECT MEMORY ACCESS BOUNDARY, UNPREDICTABLE RESULTS CAN OCCUR. WE RECOMMEND YOU CAREFULLY CHECK THE SECTOR SIZE AND THE NUMBER OF SECTORS TO BE READ OR WRITTEN TO BEFORE ISSUING THIS CALL.
The number of sectors specified is transferred between the given drive and the transfer address. Logical sector numbers (LSN) are obtained by numbering each sector sequentially starting from track 0, head 0, sector 1 (logical sector 0) and continuing along the same head, then to the next head until the last sector on the last head of the track is counted. Thus, logical sector 1 is track 0, head 0, sector 2; logical sector 2 is track 0, head 0, sector 3; and so on. Numbering continues with sector 1 on head 0 of the next track. Note that although the sectors are sequentially numbered (for example, sectors 2 and 3 on track 0 in the example above), they may not be physically adjacent on the disk, because of interleaving. Note that the mapping is different from that used by DOS version 1.10 for dual-sided diskettes.
All registers except the segment registers are destroyed by this call. If the transfer was successful, the carry flag (CF) is 0. If the transfer was not successful CF=1 and (AX) indicate the error as follows. (AL) is the DOS 4.00 error code that is the same as the error code returned in the low byte of DI when an interrupt 24H is issued, and (AH) contains:
80H Attachment failed to respond 40H SEEK operation failed 08H Bad CRC on diskette read 04H Requested sector not found 03H Write attempt on write-protected diskette 02H Error other than types listed above
WARNING: BEFORE ISSUING THIS INTERRUPT TO REMOVABLE MEDIA, THE MEDIA IN THE DRIVE MUST BE ESTABLISHED CORRECTLY. THIS CAN BE ACCOMPLISHED BY ISSUING EITHER AN INT 21H GENERIC IOCTL (AH=44H), WITH A REQUEST TO RETURN THE BPB THAT BUILD BPB RETURNS; OR AN INT 21H GET CURRENT DIRECTORY (AH=47H).
27H TERMINATE BUT STAY RESIDENT
This vector is used by programs that are to remain resident when COMMAND.COM regains control.
DOS 4.00 function call 31H is the preferred method to cause a program to remain resident, because this allows return information to be passed. It allows a program larger than 64KB to remain resident. After initializing itself, the program must set DX to its last address plus one, relative to the program's initial DS or ES value (the offset at which other programs can be loaded), and then execute an interrupt 27H. DOS 4.00 then considers the program as an extension of itself, so the program is not overlaid when other programs are executed. This concept is useful for loading programs such as user-written interrupt handlers that must remain resident.
NOTES:
1. This interrupt must not be used by .EXE programs that are loaded into the high end of memory.
2. This interrupt restores the interrupt 22H, 23H, and 24H vectors in the same manner as interrupt 20H. Therefore, it cannot be used to install permanently resident Ctrl-Break or critical error handler routines.
3. The maximum size of memory that can be made resident by this method is 64KB.
4. Memory can be used more efficiently if the block containing a copy of the environment is deallocated before terminating. This can be done by loading ES with the segment contained in 2C of the PSP, and issuing function call 49H (Free Allocated Memory).
5. DOS 4.00 function call 4CH allows the terminating program to pass a completion (or error) code to DOS 4.00, which can be interpreted within batch processing (see function call 31H).
6. Terminate-but-stay-resident function calls do not automatically close files.
28H-2EH RESERVED FOR DOS 4.00
These interrupts are reserved for DOS 4.00 use.
2FH MULTIPLEX INTERRUPT
Interrupt 2FH is the multiplex interrupt. A general interface is defined between two processes. The specific application using interrupt 2FH defines specific functions and parameters.
Every multiplex interrupt handler is assigned a specific multiplex number. The multiplex number is specified in the AH register. The specific function that the handler is to perform is specified in the AL register. Other parameters are placed in the other registers, as needed. The handlers are chained into the interrupt 2FH interrupt vector. There is no defined method for assigning a multiplex number to a handler. You must pick one. To avoid
a conflict if two applications choose the same multiplex number, the multiplex numbers used by an application should be patchable.
The multiplex numbers AH=00H through BFH are reserved for DOS 4.00. Applications should use multiplex numbers C0H through FFH.
NOTE: When in the chain for interrupt 2FH, if your code calls DOS 4.00 or if you execute with interrupts enabled, your code must be reentrant and recursive.
Function Codes
AH=1
AH=1 is the resident part of PRINT.
The following table contains the function codes that you can specify in AL to request the resident portion of print to perform a specific function:
+---------------------------------------------------------------------------+ | FUNCTION | | CODES DESCRIPTION | +---------------------------------------------------------------------------+ | 0 Get installed state | +---------------------------------------------------------------------------+ | 1 Submit file | +---------------------------------------------------------------------------+ | 2 Cancel file | +---------------------------------------------------------------------------+ | 3 Cancel all files | +---------------------------------------------------------------------------+ | 4 Status | +---------------------------------------------------------------------------+ | 5 End of status | +---------------------------------------------------------------------------+
Print Error Codes
The following table contains the error codes that are returned from the resident portion of print.
+---------------------------------------------------------------------------+ | ERROR | | CODES DESCRIPTION | +---------------------------------------------------------------------------+ | 1 Invalid function | +---------------------------------------------------------------------------+ | 2 File not found | +---------------------------------------------------------------------------+ | 3 Path not found | +---------------------------------------------------------------------------+ | 4 Too many open files | +---------------------------------------------------------------------------+ | 5 Access denied | +---------------------------------------------------------------------------+ | 6 Queue full | +---------------------------------------------------------------------------+ | 9 Busy | +---------------------------------------------------------------------------+ | 12 Name too long | +---------------------------------------------------------------------------+ | 15 Invalid drive | +---------------------------------------------------------------------------+
AL=0 Get Installed State
This call must be defined by all interrupt 2FH handlers. It is used by the caller of the handler to determine if the handler is present. On entry, AL=0, AH=1. On return, AL contains the installed state as follows:
AL=0 Not installed, permissible to install
AL=1 Not installed, not permissible to install
AL=FF Installed
AL=1 Submit File
On entry, AL=1, AH=1, and DS:DX points to the submit packet. A submit packet contains the level (BYTE) and a pointer to the ASCIIZ string (DWORD in offset segment form). The level value for DOS 4.00 is 0. The ASCIIZ string must contain the drive, path, and filename of the file you want to print. The filename cannot contain global filename characters. AL=2 Cancel File
On entry, AL=2, AH=1, and DS:DX points to the ASCIIZ string for the print file you want to cancel. Global filename characters are allowed in the filename. AL=3 Cancel all Files
On entry, AL=3 and AH=1.
AL=4 Status
This call holds the jobs in the print queue so that you can scan the queue. Issuing any other code releases the jobs. On entry, AL=4, AH=1. On return, DX contains the error count. The error count is the number of consecutive failures PRINT had while trying to output the last character. If there are no failures, the number is 0. DS:SI points to the print queue. The print queue consists of a series of filename entries. Each entry is 64 bytes long. The first entry in the queue is the file currently being printed. The end of the queue is marked by a queue entry having a null as the first character.
AL=5 End of Status: Issue this call to release the queue from call 4. On entry, AL=5 and AH=1. On return, AX contains the error codes. For information on the error codes returned, refer to "Print Error Codes" on page A-10.
AL=F8-FF Reserved by DOS 4.00
AH=6
AH=6 is the resident part of ASSIGN. The Get Installed State function (AL=0) is supported.
AH=8H, 10H, 12H, 13H Reserved by DOS 4.00
AH=B7H
AH=B7H is the resident part of APPEND. The Get Installed State function (AL=0) is supported.
AL=2 Get APPEND version This call is for distinguishing between the PC LAN APPEND and the DOS 4.00 APPEND. On return, if AX=FFFFH then the DOS 4.00 APPEND is loaded.
AL=4 Get APPEND Path Pointer (DOS 4.00 APPEND only) On return ES:DI points to the currently active APPEND path.
AL=6 Get APPEND Function State (DOS 4.00 APPEND only)
BX is returned with bits set indicating if APPEND is currently enabled and what functions are in effect.
+--------+------------------------------------------------------------------+ | BIT | FUNCTION IN EFFECT IF BIT IS ON | +--------+------------------------------------------------------------------+ | 0 | APPEND enabled | +--------+------------------------------------------------------------------+ | 13 | /PATH | +--------+------------------------------------------------------------------+ | 14 | /E | +--------+------------------------------------------------------------------+ | 15 | /X | +--------+------------------------------------------------------------------+
NOTE: The functions in effect do not change whether or not APPEND is disabled.
AL=7 Set function state (DOS 4.00 APPEND only)
On input BX is the new setting for all functions. The suggested procedure is to get the current function state, turn on or turn off the desired bits, then use this call to set the function state.
AL=11H Set Return Found Name State (DOS 4.00 APPEND only)
On request AL=17, a process system state flag is set. If this flag is set, then on the next ASCIIZ 3DH, 43H or 6CH function call within Interrupt 21H that APPEND processes, APPEND returns the name it finds to the application filename buffer. This name may be different from the one the application offered. The application must provide enough space for the found name. After APPEND has processed an
Interrupt 21H, it resets the Return Found Name state. An example of this process follows:
MOV AH,0B7H ; Indicate APPEND MOV AL,0 ; Get installed state INT 2FH CMP AL,0 ; APPEND installed? JE NOT_INSTALLED
MOV AH,0B7H ; Indicate APPEND MOV AL,2 ; Get APPEND version INT 2FH CMP AX,-1 ; DOS version? PC_LAN_APPEND ; AX<> -1 means PC LAN JNE APPEND
- The following functions are valid only if DOS 4.00 APPEND
MOV AH,0B7H ; Indicate APPEND MOV AL,4 ; Get APPEND path pointer INT 2FH
- ES
- DI = address of APPEND path
- (Buffer is 128 characters long)
MOV AH,0B7H ; Indicate APPEND MOV AL,6 ; Get function state INT 2FH
- BX = function state
- 8000H = /X is on
- 4000H = /E is on
- 2000H = /PATH is on
- 0001H = APPEND enabled
- If off, similar to null
- APPEND path
- Set on by any non-status
- occurrence of APPEND
MOV AH,0B7H ; Indicate APPEND MOV AL,7 ; Set function state MOV BX,state ; New state INT 2FH
MOV AH,0B7H ; Indicate APPEND MOV AL,11H ; Set Return Found
- Name state
INT 2FH
Example 2FH Handler
MYNUM DB X ; X = The specific AH
- multiplex number.
INT 2F NEXT DD ? ; Chain location INT 2F:
ASSUME DS:NOTHING,ES:NOTHING,SS:NOTHING
CMP AH,MYNUM JE MINE JMP INT 2F NEXT ; Chain to next
- 2FH Handler
MINE:
CMP AL,0F8H JB DO FUNC IRET ; IRET on reserved
- functions
DO FUNC:
OR AL,AL JNE NON INSTALL ; Non Get Installed
- State request
MOV AL,0FFH ; Say I'm here IRET ; All done
NON INSTALL: . . .
Installing the Handler
The following example contains the functions necessary to install a handler:
MOV AH,MYNUM XOR AL,AL INT 2FH ; Ask if already
- installed
OR AL,AL JZ OK INSTALL
BAD INSTALL: ; Handler already installed .sp 3 OK INSTALL: ; Install my
- handler
MOV AL,2FH MOV AH,GET INTERRUPT VECTOR INT 21H ; Get multiplex
- vector
MOV WORD PTR INT 2F NEXT+2,ES MOV WORD PTR INT 2F NEXT,BX MOV DX,OFFSET INT 2F MOV AL,2FH MOV AH,SET INTERRUPT VECTOR INT 21H ; Set multiplex
- vector
. . .
30H-3FH RESERVED FOR DOS 4.00
These interrupts are reserved for DOS 4.00 use.
Appendix B
APPENDIX B. DOS 4.00 FUNCTION CALLS 100 Using DOS 4.00 Function Calls 219 Program Code Fragments 230 .COM Programs 236 DOS 4.00 Registers 256 Responding to Errors 340 Extended Error Codes 355 00H -- Program Terminate 518 01H -- Console Input with Echo 546 02H -- Display Output 581 03H -- Auxiliary Input 603 04H -- Auxiliary Output 631 05H -- Printer Output 655 06H -- Direct Console I/O 672 07H -- Direct Console Input Without Echo 720 08H -- Console Input Without Echo 753 09H -- Display String 786 0AH -- Buffered Keyboard Input 815 0BH -- Check Standard Input Status 848 0CH -- Clear Keyboard Buffer and Invoke a Keyboard Function 868 0DH -- Disk Reset 885 0EH -- Select Disk 904 0FH -- Open File 937 10H -- Close File 985 11H -- Search for First Entry 1022 12H -- Search for Next Entry 1099 13H -- Delete File 1149 14H -- Sequential Read 1193 15H -- Sequential Write 1240 16H -- Create File 1286 17H -- Rename File 1330 19H -- Current Disk 1380 1AH -- Set Disk Transfer Address 1400 1BH -- Allocation Table Information 1425 1CH -- Allocation Table Information for Specific Device 1453 21H -- Random Read 1489 22H -- Random Write 1541 23H -- File Size 1599 24H -- Set Relative Record Field 1642 25H -- Set Interrupt Vector 1668 26H -- Create New Program Segment 1695 27H -- Random Block Read 1725 28H -- Random Block Write 1787 29H -- Parse Filename 1847 2AH -- Get Date 1918 2BH -- Set Date 1946 2CH -- Get Time 1979 2DH -- Set Time 2015 2EH -- Set/Reset Verify Switch 2051 2FH -- Get Disk Transfer Address (DTA) 2085 30H -- Get DOS Version Number 2108 31H -- Terminate Process and Remain Resident 2138 33H -- Get/Set System Value 2175 35H -- Get Interrupt Vector 2235 36H -- Get Disk Free Space 2262 38H -- Get or Set Country Dependent Information 2318 39H -- Create Subdirectory (MKDIR) 2431 3AH -- Remove Subdirectory (RMDIR) 2466 3BH -- Change the Current Directory (CHDIR) 2498 3CH -- Create a File (CREAT) 2530 3DH -- Open a File 2577 3EH -- Close a File Handle 2812 3FH -- Read from a File or Device 2840 40H -- Write to a File or Device 2886 41H -- Delete a File from a Specified Directory (UNLINK) 2938 42H -- Move File Read Write Pointer (LSEEK) 2971 43H -- Change File Mode (CHMOD) 3035 44H -- I/O Control for Devices 3092 45H -- Duplicate a File Handle (DUP) 3103 46H -- Force a Duplicate of a Handle (FORCDUP) 3137 47H -- Get Current Directory 3170 48H -- Allocate Memory 3202 49H -- Free Allocated Memory 3237 4AH -- Modify Allocated Memory Blocks (SETBLOCK) 3263 4BH -- Load or Execute a Program (EXEC) 3303 4CH -- Terminate a Process (EXIT) 3442 4DH -- Get Return Code of a Subprocess (WAIT) 3466 4EH -- Find First Matching File (FIND FIRST) 3494 4FH -- Find Next Matching File (FIND NEXT) 3567 54H -- Get Verify Setting 3606 56H -- Rename a File 3628 57H -- Get/Set File's Date and Time 3669 59H -- Get Extended Error 3714 5AH -- Create Unique File 3785 5BH -- Create New File 3839 5CH -- Lock/Unlock File Access 3878 5E00H -- Get Machine Name 3972 5E02H -- Set Printer Setup 4006 5E03H -- Get Printer Setup 4051 5F02H -- Get Redirection List Entry 4096 5F03H -- Redirect Device 4169 5F04H -- Cancel Redirection 4259 62H -- Get Program Segment Prefix Address 4305 65H -- Get Extended Country Information 4328 66H -- Get/Set Global Code Page 4451 67H -- Set Handle Count 4494 68H -- Commit File 4539 6CH -- Extended Open/Create 4562 APPENDIX B. DOS 4.00 FUNCTION CALLS NUMBER FUNCTION NAME 00H Program terminate 01H Console input with echo 02H Display output 03H Auxiliary input 04H Auxiliary output 05H Printer output 06H Direct console I/O 07H Direct console input without echo 08H Console input without echo 09H Display string 0AH Buffered keyboard input 0BH Check standard input status 0CH Clear keyboard buffer, invoke a keyboard function 0DH Disk reset 0EH Select disk 0FH Open file 10H Close file 11H Search for first entry 12H Search for next entry 13H Delete file 14H Sequential read 15H Sequential write 16H Create file 17H Rename file 18H Reserved by DOS 4.00 19H Current disk 1AH Set disk transfer address 1BH Allocation table information 1CH Allocation table information for specific device 1DH Reserved by DOS 4.00 1EH Reserved by DOS 4.00 1FH Reserved by DOS 4.00 20H Reserved by DOS 4.00 21H Random read 22H Random write 23H File size 24H Set relative record field 25H Set interrupt vector 26H Create new program segment 27H Random block read 28H Random block write 29H Parse filename 2AH Get date 2BH Set date 2CH Get time 2DH Set time 2EH Set/reset verify switch 2FH Get disk transfer address 30H Get DOS 4.00 version number 31H Terminate process and remain resident 32H Reserved by DOS 4.00 33H Get/Set system value 34H Reserved by DOS 4.00 35H Get interrupt vector 36H Get disk free space 37H Reserved by DOS 4.00 38H Get/set country dependent information 39H Create subdirectory (MKDIR) 3AH Remove subdirectory (RMDIR) 3BH Change current directory (CHDIR) 3CH Create a file (CREAT) 3DH Open a file 3EH Close a file handle 3FH Read from a file or device 40H Write to a file or device 41H Delete a file from a specified directory (UNLINK) 42H Move file read/write pointer (LSEEK) 43H Change file mode (CHMOD) 44H I/O control for devices (IOCtl) 45H Duplicate a file handle (DUP) 46H Force a duplicate of a file handle (FORCDUP) 47H Get current directory 48H Allocate memory 49H Free allocated memory 4AH Modify allocated memory blocks (SETBLOCK) 4BH Load or execute a program (EXEC) 4CH Terminate a process (EXIT) 4DH Get return code of a subprocess (WAIT) 4EH Find first matching file (FIND FIRST) 4FH Find next matching file (FIND NEXT) 50H Reserved by DOS 4.00 51H Reserved by DOS 4.00 52H Reserved by DOS 4.00 53H Reserved by DOS 4.00 54H Get verify setting 55H Reserved by DOS 4.00 56H Rename a file 57H Get/set a file's date and time 58H Reserved for DOS 4.00 59H Get extended error 5AH Create unique file 5BH Create new file 5CH Lock/unlock file access 5DH Reserved by DOS 4.00 5E00H Get machine name 5E02H Set printer setup 5E03H Get printer setup 5F02H Get redirection list entry 5F03H Redirect device 5F04H Cancel redirection 60H Reserved by DOS 4.00 61H Reserved by DOS 4.00 62H Get PSP address 63H Reserved by DOS 4.00 64H Reserved by DOS 4.00 65H Get extended country information 66H Get/set global code page 67H Set handle count 68H Commit file 69H Reserved by DOS 4.00 6AH Reserved 6BH Reserved by DOS 4.00 6CH Extended open/create USING DOS 4.00 FUNCTION CALLS Most function calls require input to be passed to them in registers. After setting the appropriate register values, issue the function calls in either of the following ways: The preferred method is to place the function number in AH and issue interrupt 21H. Place the function number in AH and execute a call to offset 50H in your program segment prefix. PROGRAM CODE FRAGMENTS In each of the function call descriptions in this chapter, the input, output and method of use are described using a small program code fragment. These fragments are written in IBM PC Assembler Language. .COM PROGRAMS The descriptions assume that the program is an .EXE, not a .COM program. If a .COM program is desired, do not include either of the following instructions: MOV ES,SEG -- or MOV DS,SEG -- NOTES: 1. Some FCB function calls do not permit invalid characters (0DH-29H). 2. Device names cannot end in a colon. 3. The contents of the AX register can be altered by any of the function calls. Even though no error code is returned in AX, it is possible that AX has been changed. DOS 4.00 REGISTERS DOS 4.00 uses the following registers, pointers, and flags when executing interrupts and function calls: +---------------------------------------------------------------------------+ | REGISTER GENERAL | | DEFINITION REGISTERS | +---------------------------------------------------------------------------+ | AX Accumulator (16-bit) | | AH Accumulator high-order byte (8-bit) | | AL Accumulator low-order byte (8-bit) | +---------------------------------------------------------------------------+ | BX Base (16-bit) | | BH Base high-order byte (8-bit) | | BL Base low-order byte (8-bit) | +---------------------------------------------------------------------------+ | CX Count (16-bit) | | CH Count high-order byte (8-bit) | | CL Count low-order byte (8-bit) | +---------------------------------------------------------------------------+ | DX Data (16-bit) | | DH Data high-order (8-bit) | | DL Data low-order (8-bit) | +---------------------------------------------------------------------------+ | Flags OF,DF,IF,TF,SF,ZF,AF,PF,CF | +---------------------------------------------------------------------------+ +---------------------------------------------------------------------------+ | REGISTER | | DEFINITION POINTERS | +---------------------------------------------------------------------------+ | SP Stack pointer (16-bit) | +---------------------------------------------------------------------------+ | BP Base pointer (16-bit) | +---------------------------------------------------------------------------+ | IP Instruction pointer (16-bit) | +---------------------------------------------------------------------------+ +---------------------------------------------------------------------------+ | REGISTER SEGMENT | | DEFINITION REGISTERS | +---------------------------------------------------------------------------+ | CS Code segment (16-bit) | +---------------------------------------------------------------------------+ | DS Data segment (16-bit) | +---------------------------------------------------------------------------+ | SS Stack segment (16-bit) | +---------------------------------------------------------------------------+ | ES Extra segment (16-bit) | +---------------------------------------------------------------------------+ +---------------------------------------------------------------------------+ | REGISTER INDEX | | DEFINITION REGISTERS | +---------------------------------------------------------------------------+ | DI Destination index (16-bit) | +---------------------------------------------------------------------------+ | SI Source index (16-bit) | +---------------------------------------------------------------------------+ Register Numbering Convention Each register is 16 bits long and is divided into a high and low byte. Each byte is 8 bits long. The bits are numbered from right to left. The low byte contains bits 0 through 7 and the high byte contains bits 8 through 15. The chart below shows the hexadecimal values assigned to each bit. +--------------------------------------------------------------------------+ | High Byte Low Byte | +--------------------------------------------------------------------------+ | Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 | +--------------------------------------------------------------------------+ | Hex value 8 4 2 1 8 4 2 1 8 4 2 1 8 4 2 1 | +--------------------------------------------------------------------------+ DOS 4.00 Internal Stack When DOS 4.00 gains control, it switches to an internal stack. User registers are preserved unless information is passed back to the requester as indicated in the specific requests. The user stack needs to be sufficient to accommodate the interrupt system. It is recommended that the user stack be 200H in addition to what the user needs. RESPONDING TO ERRORS Handle function calls report an error by setting the carry flag and returning the error code in AX. FCB function calls report an error by returning FFH in AL. Extended error support (59H) provides a common set of error codes and specific error information such as error classification, location, and recommended action. In most critical cases, applications can analyze the error code and take specific action. Recommended actions are intended for programs that do not understand the error codes. Programs can take advantage of extended error support both from interrupt 24H critical error handlers and after issuing interrupt 21H function calls. Do not code to specific error codes. EXTENDED ERROR CODES HEXADECIMAL DECIMAL CODE CODE MEANING 01H 1 Invalid function number 02H 2 File not found 03H 3 Path not found 04H 4 Too many open files (no handles left) 05H 5 Access denied 06H 6 Invalid handle 07H 7 Memory control blocks destroyed 08H 8 Insufficient memory 09H 9 Invalid memory block address 0AH 10 Invalid environment 0BH 11 Invalid format 0CH 12 Invalid access code 0DH 13 Invalid data 0EH 14 Reserved 0FH 15 Invalid drive was specified 10H 16 Attempt to remove the current directory 11H 17 Not same device 12H 18 No more files 13H 19 Attempt to write on write-protected diskette 14H 20 Unknown unit 15H 21 Drive not ready 16H 22 Unknown command 17H 23 Cyclic redundancy check (CRC) -- part of diskette is bad 18H 24 Bad request structure length 19H 25 Seek error 1AH 26 Unknown media type 1BH 27 Sector not found 1CH 28 Printer out of paper 1DH 29 Write fault 1EH 30 Read fault 1FH 31 General failure 20H 32 Sharing violation 21H 33 Lock violation 22H 34 Invalid disk change 23H 35 FCB unavailable 24H 36 Sharing buffer overflow 25H 37 Reserved by DOS 4.00 26H 38 Unable to complete file operation 27H-31H 39-49 Reserved by DOS 4.00 50H 80 File exists 51H 81 Reserved 52H 82 Cannot make directory entry 53H 83 Fail on INT 24 54H 84 Too many redirections 55H 85 Duplicate redirection 56H 86 Invalid password 57H 87 Invalid parameter 58H 88 Network data fault 59H 89 Function not supported by network HEXADECIMAL DECIMAL CODE CODE MEANING 5AH 90 Required system component not installed Extended Error Codes HEXADECIMAL DECIMAL CODE CODE MEANING 32H 50 Network request not supported 33H 51 Remote computer not listening 34H 52 Duplicate name on network 35H 53 Network path not found 36H 54 Network busy 37H 55 Network device no longer exists 38H 56 NETBIOS command limit exceeded 39H 57 System error; NETBIOS error 3AH 58 Incorrect response from network 3BH 59 Unexpected network error 3CH 60 Incompatible remote adapter 3DH 61 Print queue full 3EH 62 Not enough space for print file 3FH 63 Print file was cancelled 40H 64 Network name was deleted 41H 65 Access denied 42H 66 Network device type incorrect 43H 67 Network name not found 44H 68 Network name limit exceeded 45H 69 NETBIOS session limit exceeded 46H 70 Sharing temporarily paused 47H 71 Network request not accepted 48H 72 Print or disk redirection is paused 49H-4FH 73-79 Reserved Error Classes HEXADECIMAL DECIMAL VALUE VALUE DESCRIPTION 01H 1 OUT OF RESOURCE: Example: out of space or channels. 02H 2 TEMPORARY SITUATION: Something expected to disappear with time. This is not an error condition, but a temporary situation such as a locked file. 03H 3 AUTHORIZATION: Permission problem. 04H 4 INTERNAL: Internal error in system software. Probable problem with system software rather than a user or system failure. HEXADECIMAL DECIMAL VALUE VALUE DESCRIPTION 05H 5 HARDWARE FAILURE: A serious problem not the fault of user program. 06H 6 SYSTEM FAILURE: Serious failure of system software not the fault of the user, such as missing or incorrect configuration files. 07H 7 APPLICATION PROGRAM ERROR: Inconsistent requests. 08H 8 NOT FOUND: File or item not found. Inconsistent requests. 09H 9 BAD FORMAT: File or value in invalid format or type; unsuitable. 0AH 10 LOCKED: Locked file or item. 0BH 11 MEDIA: Media failure such as incorrect disk, CRC error, or defective media. 0CH 12 ALREADY EXISTS: Duplication error, such as declaring a machine name that already exists. 0DH 13 UNKNOWN: Classification does not exist or is inappropriate. Actions HEXADECIMAL DECIMAL CODE CODE DESCRIPTION 01H 1 RETRY: Retry a few times, then prompt user to determine if the program should continue or be terminated. 02H 2 DELAY RETRY: Retry several times after pause, then prompt user to determine if the program should continue or be terminated. 03H 3 USER: If the input was entered by a user, advise reentry. The error, however, may have occurred in the program itself, such as a bad drive letter or bad filename specification. 04H 4 ABORT: Abort application with cleanup. The application cannot proceed, but the system is in an orderly state and it is safe to stop the application. 05H 5 IMMEDIATE EXIT: Stop application immediately without clearing registers. Do not use the application to close files or update indexes, but exit as soon as possible. 06H 6 IGNORE: Ignore. 07H 7 RETRY AFTER USER INTERVENTION: The user needs to perform some action such as removing a diskette and inserting a different one. Then retry the operation. Locus (Location) HEXADECIMAL DECIMAL VALUE VALUE DESCRIPTION 01H 1 UNKNOWN: Not specific; not appropriate. 02H 2 BLOCK DEVICE: Related to random access mass disk storage. 03H 3 NET: Related to the network. 04H 4 SERIAL DEVICE: Related to serial devices. 05H 5 MEMORY: Related to random access memory. 00H -- PROGRAM TERMINATE PURPOSE Stops the execution of a program. EXAMPLE MOV AH,00H ; Function Call -- Terminate Program INT 21H ; Issue request to DOS ; No return COMMENTS The terminate, Ctrl-Break, and critical error exit addresses are restored to the values they had on entry to the terminating program, from the values saved in the program segment prefix. All file buffers are flushed and the handles opened by the process are closed. Any files that have changed in length and not closed are not recorded properly in the directory. Control transfers to the terminate address. This call performs exactly the same function as interrupt 20H. It is the program's responsibility to ensure that the CS register contains the segment address of its program segment prefix control block before calling this function. Function 4CH -- Terminate a Process is the preferred method for ending a program. 01H -- CONSOLE INPUT WITH ECHO PURPOSE Waits for a character to be read at the standard input device (unless one is ready), then echoes the character to the standard output device and returns the character in AL. EXAMPLE MOV AH,01H ; Function Call -- keyboard input INT 21H ; Issue request to DOS MOV Char,AL ; Save character CMP AL,0 ; Extended character ? JNE Normal Char ; No! MOV AH,01H ; Function Call -- keyboard input INT 21H ; Issue request to DOS MOV ExtChar,AL ; Save extended character Normal Char: Character LABEL WORD ; Complete character Char DB ? ; Character buffer ExtChar DB ? ; Character buffer COMMENTS The character is checked for a Ctrl-Break. If Ctrl-Break is detected, an interrupt 23H is executed. For function call 01H, extended ASCII codes require two function calls. The first call returns 00H as an indicator that the next call will return an extended code. 02H -- DISPLAY OUTPUT PURPOSE Outputs the character in DL to the standard output device. EXAMPLE MOV AH,02H ; Function Call -- Display Output MOV DL,Char ; Get character to display INT 21H ; Issue request to DOS CHAR DB ? ; Character buffer COMMENTS If the character in DL is a backspace (08), the cursor is moved left one position (nondestructive). If a Ctrl-Break is detected after the output, an interrupt 23H is executed. 03H -- AUXILIARY INPUT PURPOSE Waits for a character from the standard auxiliary device, then returns that character in AL. EXAMPLE MOV AH,03H ; Function Call -- Auxiliary Input INT 21H ; Issue request to DOS MOV Char,AL ; Save character CHAR DB ? ; Character buffer COMMENTS Auxiliary (AUX) support is unbuffered and noninterrupt driven. At startup, DOS 4.00 initializes the first auxiliary port to 2400 baud, no parity, one-stop bit, and 8-bit word. The auxiliary function calls (03H and 04H) do not return status or error codes. For greater control, you should use the ROM BIOS routine (interrupt 14H) or write an AUX device driver and use IOCtl. 04H -- AUXILIARY OUTPUT PURPOSE Outputs the character in DL to the standard auxiliary device. EXAMPLE MOV AH,04H ; Function Call -- Auxiliary Output MOV DL,Char ; Get character to output INT 21H ; Issue request to DOS ; Nothing returned CHAR DB ? ; Character buffer COMMENTS If the character in DL is a backspace (08), the cursor is moved left one position (nondestructive). If a Ctrl-Break is detected after the output, an interrupt 23H is executed. 05H -- PRINTER OUTPUT PURPOSE Outputs the character in DL to the standard printer device. EXAMPLE MOV AH,05H ; Function Call -- Printer Output MOV DL,Char ; Get character to output INT 21H ; Issue request to DOS ; Nothing returned CHAR DB ? ; Character buffer 06H -- DIRECT CONSOLE I/O PURPOSE Gets a character from the standard input device if one is ready, or outputs a character to the standard output device. EXAMPLES In loop: MOV AH,06H ; Function Call -- Direct Console I/O MOV DL,-1 ; 0FFH for input INT 21H ; Issue request to DOS JZ In loop ; No character yet on input MOV Char,AL ; Save character CMP AL,0 ; Extended Character ? JNE Normal Char ; No! MOV AH,07H ; Function Call -- Keyboard Input INT 21H ; Issue request to DOS MOV ExtChar,AL ; Save extended character Normal Char: or MOV AH,06H ; Function Call -- Direct Console I/O MOV DL,Char ; Get character to display (not 0FFH) INT 21H ; Issue request to DOS Character LABEL WORD ; Complete character Char DB ? ; Character buffer ExtChar DB ? ; Character buffer COMMENTS If DL is FFH, AL returns with the 0 flag clear and an input character from the standard input device, if one is ready. If a character is not ready, the 0 flag will be set. If DL is not FFH, DL is assumed to have a valid character that is output to the standard output device. This function does not check for Ctrl-Break, or Ctrl-PrtSc. For function call 06H, extended ASCII codes require two function calls. The first call returns 00H as an indicator that the next call will return an extended code. 07H -- DIRECT CONSOLE INPUT WITHOUT ECHO PURPOSE Waits for a character to be read at the standard input device (unless one is ready), then returns the character in AL. EXAMPLE MOV AH,07H ; Function Call -- Direct Console Input (no echo) INT 21H ; Issue request to DOS MOV Char,AL ; Save character CMP AL,0 ; Extended character ? JNE Normal Char ; No! MOV AH,07H ; Function Call -- Direct Console Input (no echo) INT 21H ; Issue request to DOS MOV ExtChar,AL ; Save extended character Normal Char: Character LABEL WORD ; Complete character Char DB ? ; Character buffer ExtChar DB ? ; Character buffer COMMENTS As with function call 06H, no checks are made on the character. For function call 07H, extended ASCII codes require two function calls. The first call returns 00H as an indicator that the next call will return an extended code. 08H -- CONSOLE INPUT WITHOUT ECHO PURPOSE Waits for a character to be read at the standard input device (unless one is ready) and returns the character in AL. EXAMPLE MOV AH,08H ; Function Call -- Console Input (no echo) INT 21H ; Issue request to DOS MOV Char,AL ; Save character CMP AL,0 ; Extended character ? JNE Normal Char; No! MOV AH,08H ; Function Call -- Console Input (no echo) INT 21H ; Issue request to DOS MOV ExtChar,AL ; Save extended character Normal Char: Character LABEL WORD ; Complete character Char DB ? ; Character buffer ExtChar DB ? ; Character buffer COMMENTS The character is checked for Ctrl-Break. If Ctrl-Break is detected, an interrupt 23H is executed. For function call 08H, extended ASCII codes require two function calls. The first call returns 00H as an indicator that the next call will return an extended code. 09H -- DISPLAY STRING PURPOSE Sends the characters in the string to the standard output device. EXAMPLE MOV AX,SEG String MOV DS,AX ;Set DS:DX to string MOV DX,OFFSET String MOV AH,09H ;Function Call - Display String INT 21H ;Issue request to DOS String DB "This string ends at the first Dollar" DB 0DH,0AH DB "$" COMMENTS The character string in memory must be terminated by a $ (24H). Each character in the string is output to the standard output device in the same form as function call 02H. ASCII codes 0DH and 0AH represent carriage return and line feed, respectively. 0AH -- BUFFERED KEYBOARD INPUT PURPOSE Reads characters from the standard input device and places them in the buffer beginning at the third byte. EXAMPLE MOV AX,SEG Buffer MOV DS,AX ;Set DS:DX to return Buffer MOV DX,OFFSET Buffer MOV AH,0AH ;Function Call-Buffered ;Keyboard Input INT 21H ;Issue request to DOS Buffer DB 128 ; Max length of input CurLen DB ? ; Number of characters input ; (excludes Return (0DH)) CurText DB 128 DUP(?) ; Up to 128 characters allowed COMMENTS The first byte of the input buffer specifies the number of characters the buffer can hold. This value cannot be 0. Reading the standard input device and filling the buffer continues until Enter is read. If the buffer fills to one less than the maximum number of characters it can hold, each additional character read is ignored and causes the bell to ring, until Enter is read. The second byte of the buffer is set to the number of characters received, excluding the carriage return (0DH), which is always the last character. 0BH -- CHECK STANDARD INPUT STATUS PURPOSE Checks if there is a character available from the standard input device. EXAMPLE In LOOP: MOV AH,0BH ; Function Call -- Check Input INT 21H ; Issue request to DOS CMP AL,-1 ; 0FFH indicates character available JNE In LOOP: COMMENTS If a character is available from the STDIN device, AL is FFH. Otherwise, AL is undefined. If a Ctrl-Break is detected, an interrupt 23H is executed. 0CH -- CLEAR KEYBOARD BUFFER AND INVOKE A KEYBOARD FUNCTION PURPOSE Clears the standard input device of any characters, then executes the function call number in AL. EXAMPLE MOV AH,0CH ; Function Call -- Clear keyboard & ; Invoke function MOV AL,Function ; Function Call to execute ; (only 01H, 06H, 07H, 08H, and 0AH are allowed). INT 21H ; Issue request to DOS ; Output depends on Function Call selected 0DH -- DISK RESET PURPOSE Writes to the disk file buffers that have been modified. All buffers are then made available for reuse. EXAMPLE MOV AH,0DH ; Function Call -- Disk Reset INT 21H ; Issue request to DOS ; No return COMMENTS It is necessary to close or commit all open files to correctly update the disk directory. 0EH -- SELECT DISK PURPOSE Selects the drive specified in DL (0=A, 1=B, etc.) (if valid) as the default drive. EXAMPLE MOV AH,0EH ; Function Call -- Select Disk MOV DL,Drive ; Drive to select (0=A:, 1=B:, ...) INT 21H ; Issue request to DOS MOV LastDrive,AL : Save max drive number (1=A:, 2=B:, ...) MOV AH,19H ; Function Call -- Get Current Disk INT 21H ; Issue request to DOS CMP AL,DL ; Selected drive = requested JNE Error ; No, Error! Drive DB ; New Drive to select LastDrive DB ; Highest Valid Drive COMMENTS The total number of unique drive letters, including diskette and fixed disk drives, that can be referenced is returned in AL. The value in AL is equal to the value of LASTDRIVE in CONFIG.SYS or the total number of installed devices, whichever is greater. For DOS 4.00 5 is the minimum value returned in AL. If the system has only one diskette drive, it is counted as two to be consistent with the philosophy of thinking of the system as having logical drives A and B. 0FH -- OPEN FILE PURPOSE Searches the current directory for the named file and AL returns FFH if it is not found. If the named file is found, AL returns 00H and the FCB is filled as described below. EXAMPLE MOV AX,SEG FCB ;Address FCB Parameter Block MOV DS,AX MOV DX,OFFSET FCB MOV AH,0FH ;Function Call-FCB Open INT 21H ;Issue request to DOS FCB LABEL BYTE Drive DB 0 ; Drive (0=Current, 1=A, 2=B, ...) FName DB "FILENAME" ; File Name (blank padded) Ext DB "EXT" ; File Extension (blank padded) DB 25 DUP(0) ; Filled in by DOS 4.00 COMMENTS AL is 00H if the file is opened. AL is FFH if the file was not opened. Use Function Call 59H (Get Extended Error) to determine the actual error condition. If the drive code was 0 (default drive), it is changed to the actual drive used (1=A, 2=B, and so on). This allows changing the default drive without interfering with subsequent operations on this file. The current block field (FCB bytes C-D) is set to 0. The size of the record to be worked with (FCB bytes E-F) is set to the system default of 80H. The size of the file and the date are set in the FCB from information obtained from the directory. You can change the default value for the record size (FCB bytes E-F) or set the random record size and/or current record field. Perform these actions after the open, but before any disk operations. The file is opened in compatibility mode. For information on compatibility mode, refer to function call 3DH. 10H -- CLOSE FILE PURPOSE Closes a file. EXAMPLE MOV AX,SEG FCB ; Address FCB Parameter Block MOV DS,AX MOV DX,OFFSET FCB MOV AH,10H ; Function Call-FCB Close INT 21H ; Issue request to DOS CMP AL,0 ; File Closed? JNE Error ; No, Error! FCB LABEL BYTE ; Contents set by previous operations COMMENTS AL is 00H if the file is closed. AL is FFH if the file was not closed. Use Function Call 59H (Get Extended Error) to determine the actual error condition. This function call must be executed on open files after file writes, and we highly recommend that it be used on all files. If the file is not found in its correct position in the current directory, it is assumed the disk was changed and AL returns FFH. Otherwise, the directory is updated to reflect the status in the FCB, the buffers for that file are flushed, and AL returns 00H. 11H -- SEARCH FOR FIRST ENTRY PURPOSE Searches the current directory for the first matching filename. EXAMPLE MOV AX,SEG DTA ; Address Buffer for found file MOV DS,AX ; information MOV DX,OFFSET DTA MOV AH,1AH ; Function Call-Set DTA address INT 21H ; Issue request to DOS MOV AX,SEG FCB ; Address FCB parameter block MOV DS,AX MOV DX,OFFSET FCB MOV AH,11H ; Function Call-FCB search first INT 21H ; Issue request to DOS CMP AL,0 ; File found? JNE Error ; No, Error! FCB LABEL BYTE Fdrive DB 0 ; Drive (0=Current, 1=A, 2=B, ...) Fname DB "FILENAME" ; File name (blank padded, may use ?) Fext DB "EXT" ; File extension (blank padded, may use ?) DB 25 DUP(0) ; Filled in by DOS DTA LABEL BYTE Ddrive DB ? ; Drive Dname DB "????????" ; File Name (blank padded) Dext DB "???" ; File Extension (blank padded) DB 25 DUP(0) ; Filled in by DOS 4.00 COMMENTS AL is 00H if the file is found. AL is FFH if the file was not found. Use Function Call 59H (Get Extended Error) to determine the actual error condition. The current disk directory is searched for the first matching filename. If none are found, AL returns FFH. Global filename characters are allowed in the filename and extension. If a matching filename is found, AL returns 00H and the locations at the disk transfer address are set as follows: If the FCB provided for searching was an extended FCB, the first byte at the disk transfer address is set to FFH followed by 5 bytes of 0, then the attribute byte from the search FCB, then the drive number used (1=A, 2=B, etc.), then the 32 bytes of the directory entry. Thus, the disk transfer address contains a valid unopened extended FCB with the same search attributes as the search FCB. If the FCB provided for searching was a standard FCB, then the first byte is set to the drive number used (1=A, 2=B), and the next 32 bytes contain the matching directory entry. Thus, the disk transfer address contains a valid unopened normal FCB. NOTES: If an extended FCB is used, the following search pattern is used: 1. If the attribute is 0, only normal file entries are found. Entries for volume label, sub-directories, hidden and system files, are not returned. 2. If the attribute field is set for hidden or system files, or directory entries, it is an inclusive search. All normal file entries, plus all entries matching the specified attributes, are returned. To look at all directory entries except the volume label, the attribute byte may be set to hidden + system + directory (all 3 bits on). 3. If the attribute field is set for the volume label, it is considered an exclusive search, and only the volume label entry is returned. 12H -- SEARCH FOR NEXT ENTRY PURPOSE Searches the current directory for the next matching filename. EXAMPLE MOV AX,SEG DTA ; Address Buffer for found file MOV DS,AX ; Information MOV DX,OFFSET DTA MOV AH,1AH ; Function Call-Set DTA address INT 21H ; Issue request to DOS MOV AX,SEG FCB ; Address FCB Parameter Block MOV DS,AX MOV DX,OFFSET FCB MOV AH,12H ; Function Call-FCB Search Next INT 21H ; Issue request to DOS CMP AL,0 ; File found? JNE Error ; No, Error! FCB LABEL BYTE ; As set by FCB Search First DTA LABEL BYTE Drive DB ? ; Drive Fname DB "????????" ; File Name (blank padded) Ext DB "???" ; File Extension (blank padded) DB 25 DUP(0) ; Filled in by DOS 4.00 COMMENTS AL is 00H if the file is found. AL is FFH if the file was not found. Use Function Call 59H (Get Extended Error) to determine the actual error condition. After a matching filename has been found using function call 11H, function 12H may be called to find the next match to an ambiguous request. The DTA contains information from the previous Search First or Search Next. All of the FCB, except for the name/extension field, is used to keep information necessary for continuing the search, so no disk operations may be performed if this FCB is between a previous function 11H or 12H call and this one. 13H -- DELETE FILE PURPOSE Deletes all current directory entries that match the specified filename. The specified filename cannot be read-only. EXAMPLE MOV AX,SEG FCB ;Address FCB Parameter Block MOV DS,AX MOV DX,OFFSET FCB MOV AH,13H ;Function Call-FCB Delete File INT 21H ;Issue request to DOS CMP AL,0 ;File(s) Deleted? JNE Error ;No, Error! FCB LABEL BYTE Drive DB 0 ; Drive FName DB Filename ; File Name (blank padded, may Ext DB Ext ; File Extension (blank padded, may DB 25 DUP(0) ; Filled in by DOS COMMENTS AL is 00H if the file is found. AL is FFH if the file was not found. Use Function Call 59H (Get Extended Error) to determine the actual error condition. All matching current directory entries are deleted. The global filename character "?" is allowed in the filename or extension. If no directory entries match, AL returns FFH; otherwise AL returns 00H. If the file is specified in read-only mode, the file is not deleted. NOTE: Close open files before deleting them. Network Access Rights: Requires Create access rights. 14H -- SEQUENTIAL READ PURPOSE Loads the record addressed by the current block (FCB bytes C-D) and the current record (FCB byte 1F) at the disk transfer address (DTA), then the record address is increased. EXAMPLE MOV AX,SEG DTA ;Address Data buffer MOV DS,AX MOV DX,OFFSET DTA MOV AH,1AH ;Function call Set DTA Address INT 21H ;Issue request to DOS MOV AX,SEG FCB ;Address FCB Parameter Block MOV DS,AX MOV DX,OFFSET FCB MOV AH,14H ;Function Call-FCB Sequential Read INT 21H ;Issue request to DOS CMP AL,0 ;Data Read? JNE Error ;No, Error! FCB LABEL BYTE ; Set by previous open DTA LABEL BYTE DB ?Dup(0) ;I/O buffer COMMENTS AL is 00H if the read was successful. AL is 01H if the file was at End of File (EOF). AL is 02H if the read would have caused a wrap or overflow because the DTA was too small (the read was not completed). AL is 03H if EOF (a partial record was read and filled out with 0's). Use Function Call 59H (Get Extended Error) to determine the actual error condition. The length of the record is determined by the FCB record size field. Network Access Rights: Requires Read access rights. 15H -- SEQUENTIAL WRITE PURPOSE Writes the record addressed by the current block and record fields (size determined by the FCB record size field) from the disk transfer address. If records are less than the sector size, the record is buffered for an eventual write when a sector's worth of data is accumulated. Then the record address is increased. EXAMPLE MOV AX,SEG DTA ;Address Data buffer MOV DS,AX MOV DX,OFFSET DTA MOV AH,1AH ;Function Set DTA Address INT 21H ;Issue request to DOS MOV AX,SEG FCB ;Address FCB Parameter Block MOV DS,AX MOV DX,OFFSET FCB MOV AH,15H ;Function Call-FCB Sequential Write INT 21H ;Issue request to DOS CMP AL,0 ;Data Written? JNE Error ;No, Error! FCB LABEL BYTE ; Set by previous open DTA LABEL BYTE DB ?Dup(0) ;I/O buffer COMMENTS AL is 00H if the write was successful. AL is 01H if the disk or diskette is full (write cancelled). AL is 02H if the write would have caused a wrap or overflow because the DTA was too small (write cancelled). Use Function Call 59H (Get Extended Error) to determine the actual error condition. If the file is specified in read-only mode, the sequential write is not performed and 01H is returned in AL. Network Access Rights: Requires Write access rights. 16H -- CREATE FILE PURPOSE Creates a new file. EXAMPLE MOV AX,SEG FCB ;Address FCB parameter block MOV DS,AX MOV DX,OFFSET FCB MOV AH,16H ;Function Call-FCB create file INT 21H ;Issue request to DOS CMP AL,0 ;File created and opened? JNE Error ;No, Error! FCB LABEL BYTE Fdrive DB 0 ; Drive (0=Current, 1=A, 2=B, ...) Fname DB "FILENAME" ; File name (blank padded) Fext DB "EXT" ; File extension (blank padded) DB 25 DUP(0) ; Filled in by DOS COMMENTS AL is 00H if the file is created and opened. AL is FFH if the file was not created (normally a full directory or disk full). Use Function Call 59H (Get Extended Error) to determine the actual error condition. If a matching entry is found it is reused. If no match is found, the directory is searched for an empty entry. If a match is found, the entry is initialized to a 0-length file, the file is opened (see function call 0FH), and AL returns 00H. The file may be marked hidden during its creation by using an extended FCB containing the appropriate attribute byte. Network Access Rights: Requires Create access rights. 17H -- RENAME FILE PURPOSE Changes every matching occurrence of the first filename in the current directory of the specified drive to the second, with the restriction that two files cannot have the same name and extension. EXAMPLE MOV AX,SEG FCB ;Address FCB Parameter Block MOV DS,AX MOV DX,OFFSET FCB MOV AH,17H ;Function Call-FCB Rename File INT 21H ;Issue request to DOS CMP AL,0 ;File(s) Renamed? JNE Error ;No, Error! FCB LABEL BYTE Fdrive DB 0 ; Drive (0=Current, 1=A, 2=B, ...) Fname DB "FILENAME" ; File Name (blank padded, may use ? Fext DB "EXT" ; File Extension (blank padded, may use ? DB 5 DUP(0) ; Reserved NewName DB "FILENAME" ; New File Name (blank padded, may use ? NewExt DB "EXT" ; New File Extension (blank padded, may use ? DB 7 DUP(0) ; Reserved COMMENTS AL is 00H if the file or files were renamed. AL is FFH if a file in the current directory did not match or the new name already exists. Use Function Call 59H (Get Extended Error) to determine the actual error condition. The modified FCB has a drive code and filename in the usual position, and a second filename on the sixth byte after the first (DS:DX+11H) in what is normally a reserved area. If "?"s appear in the second name, the corresponding positions in the original name are unchanged. If the file is specified in read-only mode, the file is not renamed. Network Access Rights: Requires Create access rights. 19H -- CURRENT DISK PURPOSE Determines the current default drive. EXAMPLE MOV AH,19H ; Function Call -- Get Current Disk INT 21H ; Issue request to DOS MOV Disk,AL ; Save Current Disk Disk DB ? ; Current Disk code (0=A:, 1=B:, ...) COMMENTS AL returns with the code of the current default drive (0=A, 1=B, and others.). 1AH -- SET DISK TRANSFER ADDRESS PURPOSE Sets the disk transfer address to DS:DX. EXAMPLE MOV AX,SEG DTA ;Address Buffer MOV DS,AX MOV DX,OFFSET DTA MOV AH,1AH ;Function Call-Set DTA address INT 21H ;Issue request to DOS DTA LABEL BYTE ; Data Buffer COMMENTS The area defined by this call is from the address in DS:DX to the end of the segment in DS. DOS 4.00 does not allow disk transfers to wrap around within the segment, or overflow into the next segment. If you do not set the DTA, the default DTA is offset 80H in the program segment prefix. To get the DTA, issue function call 2FH. 1BH -- ALLOCATION TABLE INFORMATION PURPOSE Returns information about the allocation table for the default drive. EXAMPLE MOV AH,1BH ; Function Call -- Allocation Table ; Information INT 21H ; Issue request to DOS MOV NumAllocUnits,DX ; Save Number of Allocation Units MOV NumSectsAllocUnit,AL ; Save Number of Sectors/Allocation Unit MOV SectSize,CX ; Save of Sector Size MOV WORD PTR MediaType@+0,BX; Save Pointer to Media Type Byte MOV WORD PTR MediaType@+2,DS NumAllocUnits DW ? ; Number of Allocation Units on Current NumSectsAllocUnit DB ? ; Number Sectors in an Allocation Unit SectSize DW ? ; Sector Size MediaType@ DD ? ; Pointer to Media Type byte COMMENTS Refer to function call 36H (Get Disk Free Space). 1CH -- ALLOCATION TABLE INFORMATION FOR SPECIFIC DEVICE PURPOSE Returns allocation table information for a specific device. EXAMPLE MOV AH,1CH ; Function Call -- ; Allocation Table Information MOV DL,Drive ; Drive requested (0=current, ; 1=A:, ...) INT 21H ; Issue request to DOS MOV NumAllocUnits,DX ; Save Number of Allocation Units MOV NumSectsAllocUnit,AL ; Save Number of Sectors/Allocation Unit MOV SectSize,CX ; Save of Sector Size MOV WORD PTR MediaType@+0,BX ; Save Pointer to Media Type Byte MOV WORD PTR MediaType@+2,DS Drive DB ; drive number to get info for NumAllocUnits DW ? ; Number of Allocation Units ; on specified drive NumSectsAllocUnit DB ? ; Number Sectors in an ; Allocation Unit SectSize DW ? ; Sector Size MediaType@ DD ? ; Pointer to Media Type byte COMMENTS This call is the same as call 1BH, except that on entry DL contains the number of the drive that contains the needed information (0 = default, 1 = A, and so forth.). For more information on DOS 4.00 disk allocation, refer to "The Disk Directory" on page 2-3. Also, refer to function call 36H (Get Disk Free Space). 21H -- RANDOM READ PURPOSE Reads the record addressed by the current block and current record fields into memory at the current disk transfer address. EXAMPLE ;Set up FCB MOV AX,SEG DTA ;Address Data buffer MOV DS,AX MOV DX,OFFSET DTA MOV AH,1AH ;Function Set DTA Address INT 21H ;Issue request to DOS MOV AX,SEG FCB ;Address FCB Parameter Block MOV DS,AX MOV DX,OFFSET FCB MOV AH,21H ;Function Call-FCB Random Read INT 21H ;Issue request to DOS CMP AL,0 ;Data Read? JNE Error ;No, Error! FCB LABEL BYTE ; Set by previous open ; DTA label byte COMMENTS AL is 00H if the read was successful. AL is 01H if the file was at End of File (EOF) (no data read). AL is 02H if the read would have caused a wrap or overflow because the DTA was too small (the read was not completed). AL is 03H if EOF (a partial record was read and filled out with 0's). Use Function Call 59H (Get Extended Error) to determine the actual error condition. The current block and current record fields are set to agree with the random record field. The record addressed by these fields is read into memory at the current disk transfer address. For information on record size see Chapter 4, "Accessing Files Using File Control Blocks" on page 4-1. NOTE: Function 24H must be called before using this function. Network Access Rights: Requires Read access rights. 22H -- RANDOM WRITE PURPOSE Writes the record addressed by the current block and current record fields from the current disk transfer address. EXAMPLE ;Set up FCB MOV AX,SEG FCB ;Address FCB parameter block MOV DS,AX MOV DX,OFFSET FCB MOV AH,24H ;Function Call--FCB Set ;Relative record field INT 21H ;Issue request to DOS MOV AX,SEG DTA ;Address data buffer MOV DS,AX MOV DX,OFFSET DTA MOV AH,1AH ;Function Set DTA address INT 21H ;Issue request to DOS MOV AX,SEG FCB ;Address FCB parameter block MOV DS,AX MOV DX,OFFSET FCB MOV AH,22H ;Function Call-FCB random writers INT 21H ;Issue request to DOS CMP AL,0 ;Data written? JNE Error ;No, error! FCB LABEL BYTE ; Set by previous open DTA LABEL BYTE COMMENTS AL is 00H if the write was successful. AL is 01H if the write or diskette is full (write cancelled). AL is 02H if the read would have caused a wrap or overflow because the DTA was too small (write cancelled). Use Function Call 59H (Get Extended Error) to determine the actual error condition. The current block and current record fields are set to agree with the random record field. Then the record addressed by these fields is written (or in the case of records not the same as sector sizes -- buffered) from the disk transfer address. If the file is specified in read-only mode, the random write is not performed. Network Access Rights: Requires Write access rights. 23H -- FILE SIZE PURPOSE Searches the current directory for an entry that matches the specified file and sets the FCBs random record field to the number of records in the file. EXAMPLE MOV AX,SEG FCB ; Address FCB parameter block MOV DS,AX MOV DX,OFFSET FCB MOV AH,23H ; Function Call-FCB file size INT 21H ; Issue request to DOS CMP AL,0 ; File found? JNE Error ; No, error! FCB LABEL BYTE Drive DB 0 ; Drive (0=Current, 1=A, 2=B, ...) Name DB "FILENAME" ; File name (blank padded) Ext DB "EXT" ; File extension (blank padded) DB 25 DUP(0) ; Filled in by DOS COMMENTS AL is 00H if the file exists. AL is FFH if the file was not created (normally a full directory or disk full). Use Function Call 59H (Get Extended Error) to determine the actual error condition. The directory is searched for the matching entry. If a matching entry is found, the random record field is set to the number of records in the file (in terms of the record size field rounded up). If no matching entry is found, AL returns FFH. NOTE: If you do not set the FCB record size field before using this function, incorrect information is returned. 24H -- SET RELATIVE RECORD FIELD PURPOSE Sets the random record field to the same file address as the current block and record fields. EXAMPLE MOV AX,SEG FCB ;Address FCB parameter block MOV DS,AX MOV DX,OFFSET FCB MOV AH,24H ;Function Call--FCB set ;Relative record field INT 21H ;Issue request to DOS FCB LABEL BYTE ; Set by previous open COMMENTS You must call this function before you perform random reads and writes, and random block reads and writes. 25H -- SET INTERRUPT VECTOR PURPOSE Sets the interrupt vector table for the interrupt number. EXAMPLE MOV AX,SEG Handler ;Address new handler MOV DS,AX MOV DX,OFFSET Handler MOV AH,25H ;Function Call - Set Interrupt ;Vector MOV AL,Vector INT 21H ;Issue request to DOS Vector DB ? ;Number of vector to be replaced Handler: ;Code to process interrupt COMMENTS The interrupt vector table for the interrupt number specified in AL is set to address contained in DS:DX. Use function call 35H (Get Interrupt Vector) to obtain the contents of the interrupt vector. 26H -- CREATE NEW PROGRAM SEGMENT PURPOSE Creates a new program segment. EXAMPLE MOV AH,26H ; Function Call -- Create Program ; Segment MOV DX,SEG PSP ; Segment address to create new PSP INT 21H ; Issue request to DOS PSP LABEL BYTE ; Area to fill in DB 100H DUP(0) COMMENTS The entire 100H area at location 0 in the current program segment is copied into location 0 in the new program segment. The memory size information at location 6 in the new segment is updated and the current termination, Ctrl-Break exit and critical error addresses from interrupt vector table entries for interrupts 22H, 23H, and 24H are saved in the new program segment starting at 0AH. They are restored from this area when the program ends. NOTE: The EXEC function call 4BH provides a more complete service. Therefore, you should use the EXEC 4BH and avoid using this call. 27H -- RANDOM BLOCK READ PURPOSE Reads the specified number of records (in terms of the record size field) from the file address specified by the random record field into the disk transfer address. EXAMPLE ;Set up disk transfer address MOV AX,SEG DTA ;Address data buffer MOV DS,AX MOV DX,OFFSET DTA MOV AH,1AH ;Function set DTA address INT 21H ;Issue request to DOS MOV AX,SEG FCB ;Address FCB parameter block MOV DS,AX MOV DX,OFFSET FCB MOV AH,24H ;Function Call -- FCB Set ;Relative Record Field INT 21H ;Issue request to DOS MOV AX,SEG FCB ;Address FCB parameter block MOV DS,AX MOV DX,OFFSET FCB MOV CX,Records to read ;number of records to read MOV AH,27H ;Function Call - FCB random block read INT 21H ;Issue request to DOS CMP AL,0 ;Data read? JNE Error ;No, error! FCB LABEL BYTE ; Set by previous open DTA LABEL BYTE DB ?Dup(0) ;I/O buffer Records to read DW ? COMMENTS AL is 00H if the read was successful. AL is 01H if the file was at End of File (EOF) (no data read). AL is 02H if the read would have caused a wrap or overflow because the DTA was too small (the read was not completed.). AL is 03H if EOF (a partial record was read and filled out with zeros). Use Function Call 59H (Get Extended Error) to determine the actual error condition. The random record field and the current block/record fields are set to address the next record (the first record not read). NOTE: Function 24H must be called before using this function. Network Access Rights: Requires Read access rights. 28H -- RANDOM BLOCK WRITE PURPOSE Writes the specified number of records from the disk transfer address into the file address specified by the random record field. EXAMPLE ;Set up disk transfer address MOV AX,SEG DTA ;Address data buffer MOV DS,AX MOV DX,OFFSET DTA MOV AH,1AH ;Function set DTA address INT 21H ;Issue request to DOS MOV AX,SEG FCB ;Address FCB parameter block MOV DS,AX MOV DX,OFFSET FCB MOV AH,24H ;Function Call--FCB set ;Relative record field INT 21H ;Issue request to DOS MOV AX,SEG FCB ;Address FCB parameter block MOV DS,AX MOV DX,OFFSET FCB MOV CX,Records to write ;Number of records to write MOV AH,28H ;Function Call - FCB Random Block write INT 21H ;Issue request to DOS CMP AL,0 ;Data written? JNE Error ;No, error! DTA LABEL BYTE DB ?DUP(0) ; I/O Buffer COMMENTS AL is 00H if the write was successful. AL is 01H if the disk or diskette is full (write cancelled). AL is 02H if the write would have caused a wrap or overflow because the DTA was too small (write cancelled). Use Function Call 59H (Get Extended Error) to determine the actual error condition. If there is insufficient space on the disk, AL returns 01H and no records are written. If CX is 0 upon entry, no records are written, but the file is set to the length specified by the random record field, whether longer or shorter than the current file size. (Allocation units are released or allocated as appropriate.) NOTE: Function call 24H must be called before using this function. Network Access Rights: Requires Write access rights. 29H -- PARSE FILENAME PURPOSE Parses the specified filename. EXAMPLE MOV AX,SEG CmdBuf MOV DS,AX ;Address command string MOV SI,OFFSET CmdBuf MOV AX,SEG FCB MOV ES,AX ;Address FCB Parameter Block MOV DI,OFFSET FCB MOV AH,29H ;Function Call - FCB Parse Filename MOV AL,OPTIONS ;Set desired action INT 21H ;Issue request to DOS CMP AL,-1 ;Drive valid? JE Error ;No, Error! CmdBuf LABEL BYTE DB " a:file.ext ",0DH FCB LABEL BYTE ; Created in a pre-open state based on input found. Options DB ? ;parsing options COMMENTS The contents of AL are used to determine the action to take, as shown below: <must = 0> bit: 7 6 5 4 3 2 1 0 If bit 0 = 1, leading separators are scanned off the command line at DS:SI. Otherwise, no scan-off of leading separators takes place. If bit 1 = 1, the drive ID byte in the FCB will be set (changed) only if a drive was specified in the command line being parsed. If bit 2 = 1, the filename in the FCB will be changed only if the command line contains a filename. If bit 3 = 1, the filename extension in the FCB will be changed only if the command line contains a filename extension. Filename separators include the following characters: : . : , = + along with TAB and SPACE. Filename terminators include all of these characters plus ,<, >, |, /, ', [, ], and any control characters. Output: AL is 00H if no global characters (? or *) were found in the Command String. AL is 01H if global characters (? or *) were found in the Command String. AL is FFH if the drive specified is invalid. The command line is parsed for a filename of the form d:filename.ext, and if found, a corresponding unopened FCB is created at ES:DI. If no drive specifier is present, it is assumed to be all blanks. If the character * appears in the filename or extension, it and all remaining characters in the name or extension are set to ?. DS:SI returns pointing to the first character after the filename and ES:DI points to the first byte of the formatted FCB. If no valid filename is present, ES:DI+1 contains a blank. 2AH -- GET DATE PURPOSE Returns the day of the week, the year, month and date. EXAMPLE MOV AH,2AH ; Function Call -- Get Date INT 21H ; Issue request to DOS MOV DayofWeek,AL ; Save Day of the Week MOV Year,CX ; Save Year MOV Month,DH ; Save Month MOV Day,DL ; Save Day DayofWeek DB ? ; 0=Sunday, ... 6=Saturday Year DW ? ; 1980 to 2099 Month DB ? ; 1 to 12 Day DB ? ; 1 to 31 COMMENTS If the time-of-day clock rolls over to the next day, the date is adjusted accordingly, taking into account the number of days in each month and leap years. 2BH -- SET DATE PURPOSE Sets the date (also sets CMOS clock, if present). EXAMPLE MOV AH,2BH ; Function Call -- Set Date MOV CX,Year ; Set Year MOV DH,Month ; Set Month MOV DL,Day ; Set Day INT 21H ; Issue request to DOS CMP AL,0 ; Valid Date? JNE Error ; No! Year DW ? ; 1980 to 2099 Month DB ? ; 1 to 12 Day DB ? ; 1 to 31 COMMENTS AL is 00H if the date is valid and the operation is successful. AL is FFH if the date is not valid. On entry, CX:DX must have a valid date in the same format as returned by function call 2AH. On return, AL returns 00H if the date is valid and the set operation is successful. AL returns FFH if the date is not valid. 2CH -- GET TIME PURPOSE Returns the time; hours, minutes, seconds and hundredths of seconds. EXAMPLE MOV AH,2CH ; Function Call -- ; Get Time INT 21H ; Issue request to DOS MOV Hour,CH ; Save Hour MOV Minute,CL ; Save Minute MOV Second,DH ; Save Second MOV Hundredth,DL ; Save Partial Second Hour DB ? ; 0 to 23 Minute DB ? ; 0 to 59 Second DB ? ; 0 to 59 Hundredth DB ? ; 0 to 99 COMMENTS On entry, AH contains 2CH. On return, CX:DX contains the time-of-day. Time is actually represented as four 8-bit binary quantities as follows: CH Hours (0-23) CL Minutes (0-59) DH Seconds (0-59) DL 1/100 seconds (0-99). This format is readily converted to a printable form yet can also be used for calculations, such as subtracting one time value from another. 2DH -- SET TIME PURPOSE Sets the time (also sets the CMOS clock, if present). EXAMPLE MOV AH,2DH ; Function Call -- Set Time MOV CH,Hour ; Sst Hour MOV CL,Minute ; Set Minute MOV DH,Second ; Set Second MOV DL,Hundredth ; Set Partial Second INT 21H ; Issue request to DOS CMP AL,0 ; Valid Time? JNE Error ; No! Hour DB ? ; 0 to 23 Minute DB ? ; 0 to 59 Second DB ? ; 0 to 59 Hundredth DB ? ; 0 to 99 COMMENTS AL is 00H if the time is valid. AL is FFH if the time is not valid. On entry, CX:DX has time in the same format as returned by function 2CH. On return, if any component of the time is not valid, the set operation is cancelled and AL returns FFH. If the time is valid, AL returns 00H. If your system has a CMOS realtime clock, it will be set. 2EH -- SET/RESET VERIFY SWITCH PURPOSE Sets the verify switch. EXAMPLE ; To set VERIFY=OFF MOV AH,2EH ; Function Call -- Set ; VERIFY MOV AL,0 ; Set OFF INT 21H ; Issue request to DOS ; To set VERIFY=ON MOV AH,2EH ; Function Call -- Set ; VERIFY MOV AL,1 ; Set ON INT 21H ; Issue request to DOS COMMENTS On entry, AL must contain 01H to turn verify on, or 00H to turn verify off. When verify is on, DOS 4.00 performs a verify operation each time it performs a disk write to assure proper data recording. Although disk recording errors are very rare, this function has been provided for applications in which you may wish to verify the proper recording of critical data. You can obtain the current setting of the verify switch through function call 54H. NOTE: Verification is not supported on data written to a network disk. 2FH -- GET DISK TRANSFER ADDRESS (DTA) PURPOSE Returns the current disk transfer address. EXAMPLE MOV AH,2FH ; Function Call -- Get ; DTA Address INT 21H ; Issue request to DOS MOV WORD PTR DTA@+0,BX ; Save Address MOV WORD PTR DTA@+2,ES DTA@ DD ? ; DTA Buffer COMMENTS On entry, AH contains 2FH. On return, ES:BX contains the current Disk Transfer Address. You can set the DTA using function call 1AH. 30H -- GET DOS VERSION NUMBER PURPOSE Returns the DOS version number. EXAMPLE PUSH CX ; CX and BX destroyed in call PUSH BX MOV AH,30H ; Function Call -- Get DOS 4.00 ; Version INT 21H ; Issue request to DOS MOV MajorVersion,AL ; Save Version MOV MinorVersion,AH POP BX POP CX MajorVersion DB ? ; X of X.YY MinorVersion DB ? ; YY of X.YY COMMENTS On entry, AH contains 30H. On return, BX and CX are set to 0. AL contains the major version number. AH contains the minor version number. If AL returns a major version number of 0, you can assume that the DOS version is pre-DOS 2.00. 31H -- TERMINATE PROCESS AND REMAIN RESIDENT PURPOSE Terminates the current process and attempts to set the initial allocation block to the memory size in paragraphs. EXAMPLE MOV AH,31H ; Function Call -- Terminate ; and Keep Process MOV AL,RetCode ; Set value of ERRORLEVEL MOV DX,MySize ; Set my program and data size INT 21H ; Issue request to DOS INT 20H ; Be safe if on DOS 4.00 Version 1.X RetCode DB ? ; Value to return to my EXEC'er MySize DW ? ; Size of my code and data ; (in paragraphs) COMMENTS On entry, AL contains a binary return code. DX contains the memory size value in paragraphs. This function call does not free up any other allocation blocks belonging to that process. Files opened by the process are not closed when the call is executed. The return code passed in AL is retrievable by the parent through Wait (function call 4DH) and can be tested through the ERRORLEVEL batch subcommands. Memory is used efficiently if the block containing a copy of the environment is deallocated before terminating. This can be done by loading ES with the segment contained in 2C of the PSP, and issuing function call 49H (Free Allocated Memory). The five standard handles, 0000 through 0004, should be closed before exiting. 33H -- GET/SET SYSTEM VALUE PURPOSE Set or get the state of System Values such as BREAK (Ctrl-Break checking). EXAMPLE ; To check BREAK state MOV AH,33H ; Function Call -- Get/Set ; System value MOV AL,0 ; Do Get BREAK INT 21H ; Issue request to DOS MOV BREAK,DL ; Save state ; To set BREAK=OFF MOV AH,33H ; Function Call -- Get/Set ; System value MOV AL,1 ; Do Set BREAK MOV DL,0 ; Set OFF INT 21H ; Issue request to DOS ; To set BREAK=ON MOV AH,33H ; Function Call -- Get/Set ; System Value MOV AL,1 ; Do Set BREAK MOV DL,1 ; Set ON INT 21H ; Issue request to DOS ; To get the Boot Drive MOV AH,33H ; Function Call -- Get/Set ; System Value MOV AL,5 ; Do Get Boot Drive INT 21H ; Issue request to DOS MOV Drive,DL ; Save boot drive BREAK DB ? ; Current BREAK state (0=OFF, 1=ON) Drive DB ? ; DOS 4.00 boot drive COMMENTS For BREAK: AL contains 00H to request the current state of Ctrl-Break checking. On return DL contains the current state (00H = OFF, 01H = ON). AL contains 01H to set the state. DL contains the new state (00H = OFF, 01H = ON). For boot drive: AL contains 05H to request the boot drive. On return DL contains the drive (A:=1, C:=3, ...). 35H -- GET INTERRUPT VECTOR PURPOSE To obtain the address in an interrupt vector. EXAMPLE MOV AH,35H ; Function Call -- ; Set Interrupt Vector MOV AL,Vector ; Vector to get (0 to 255) INT 21H ; Issue request to DOS MOV WORD PTR OldVect+0,BX MOV WORD PTR OldVect+2,ES OldVect DD ? ; Previous vector contents Vector DB ? ; Vector number to get COMMENTS On entry, AH contains 35H. AL contains a hexadecimal interrupt number. On return, ES:BX contains the CS:IP interrupt vector for the specified interrupt. Use function call 25H (Set Interrupt Vector) to set the interrupt vectors. 36H -- GET DISK FREE SPACE PURPOSE Returns the disk free space (available clusters, clusters/drive, bytes/sector). EXAMPLE MOV AH,36H ; Function Call -- ; Get disk free space MOV DL,Drive ; Drive to query ; (0=current, 1=A:, ; 2=B:, ...) INT 21H ; Issue request to DOS CMP AX,-1 ; Error? JE Error ; Yes MOV SectAU,AX ; Save allocation unit ; Size MOV AvailAU,BX ; Save free allocation ; Units MOV SectSize,CX ; Save sector size MOV TotalAU,DX ; Save disk size MOV AX,SectSize ; Calculate allocation ; Unit size MUL SectAU MOV CX,AX ; CX = bytes/AU MOV AX,TotalAU ; Calculate total space MUL CX MOV WORD PTR TotalBytes+0,AX ; Save it MOV WORD PTR TotalBytes+2,DX MOV AX,AvailAU ; Calculate free space MUL CX MOV WORD PTR FreeBytes+0,AX ; Save it MOV WORD PTR FreeBytes+2,DX SectAU DW ? ; Sectors in an ; Allocation unit AvailAU DW ? ; Free allocation units SectSize DW ? ; Bytes in a sector TotalAU DW ? ; Number of allocation ; Units on DL disk TotalBytes DD ? ; Disk size in bytes FreeBytes DD ? ; Free space in bytes Drive DD ? ; Drive number to get info for COMMENTS If the drive number in DL was valid, BX contains the number of available allocation units, DX contains the total number of allocation units on the drive, CX contains the number of bytes per sector, and AX contains the number of sectors for each allocation unit. 38H -- GET OR SET COUNTRY DEPENDENT INFORMATION PURPOSE Sets the Active Country or returns country dependent information. EXAMPLE ; To set the Current Country MOV AH,38H ; Function Call -- Get/Set ; Country Information MOV AL,CountryID ; Country ID (-1 if >= 255) MOV BX,CountryIDX ; Country ID (if AL=-1) MOV DX,-1 ; Indicate set country code INT 21H ; Issue request to DOS JC Error ; Error code in AX ; To get Country Information MOV AX,SEG Buffer MOV DS,AX MOV DX,OFFSET Buffer MOV AH,38H MOV AL,CountryID ; Country ID (-1 if >= 255) ; (0 to get current country) MOV BX,CountryIDX ; Country ID (if AL=-1) INT 21H ; Issue request to DOS JC Error ; Error code in AX MOV CountryCode,BX ; Save current Country Code CountryCode DW ? ; Current country code CountryIDX DW ? ; Extended country code for input Buffer LABEL WORD ; Country information (see format below) CountryID DB ? ; Country code for input COUNTRY INFORMATION DateFormat DW ? ; Date Format: ; 0 = m d y order ; 1 = d m y order ; 2 = y m d order $Symbol DB "????",0 ; Currency Symbol ; example: "DM",0,?,? Sep1000 DB "?",0 ; Thousands Separator ; example: ",",0 Sep1 DB "?",0 ; Fractions Separator ; example: ".",0 SepDate DB "?",0 ; Date Separator ; example: "/",0 SepTime DB "?",0 ; Time Separator ; example: ":",0 $Format DB ? ; Currency Format: ; 0 = currency symbol, value ; 1 = value, currency symbol ; 2 = currency symbol, space, value ; 3 = value, space, currency symbol ; 4 = currency symbol is decimal separat SigDigits DB ? ; Number of Significant Digits in Currency TimeFormat DB ? ; Time Format: ; 0 = 12 hour clock ; 1 = 24 hour clock UpperCaseAL@ DD ? ; Address of Routine to Upper Case AL ; Only for values >=80H SepData DB "?",0 ; Data List Separator ; example: ",",0 Reserved DW 5 DUP(?) ; Reserved for future COMMENTS The date format has the following values and meaning: CODE DATE 0=USA m d y 1=EUROPE d m y 2=JAPAN y m d Case Map Call Address: The register contents for the case map call are: +---------------------------------------------------------------------------+ | ON REGISTER | | ENTRY CONTENTS | +---------------------------------------------------------------------------+ | AL ASCII code of character to be converted to uppercase | +---------------------------------------------------------------------------+ +---------------------------------------------------------------------------+ | ON REGISTER | | RETURN CONTENTS | +---------------------------------------------------------------------------+ | AL ASCII code of the uppercase input character | +---------------------------------------------------------------------------+ The case map call address is in a form suitable for a FAR call indirect. RETURNS Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. Function Call 65H, (Get Extended Country Information), returns more country information and is preferred. Setting the Current County Code by using this function call is not recommended. The user can set it by placing a COUNTRY command in the CONFIG.SYS file. The Country Code set by the user should not be changed. The NLSFUNC DOS 4.00 extension must be installed to change the Current Country. 39H -- CREATE SUBDIRECTORY (MKDIR) PURPOSE Creates the specified directory. EXAMPLE MOV AX,SEG DName ;Directory Name MOV DS,AX MOV DX,OFFSET DName MOV AH,39H ;Function-Make a directory INT 21H ;Issue request to DOS JC Error DName DB "?? .. ??",0 ; ASCIIZ Name ; Example: ; "c:\dir",0 COMMENTS On entry, DS:DX contains the address of an ASCIIZ string with drive and directory path names. All directory levels other than the last one in the name must exist before using this function. Only one directory level at a time can be created with this function. The maximum length of the ASCIIZ string is 64 characters. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. Network Access Rights: Requires Create access rights. 3AH -- REMOVE SUBDIRECTORY (RMDIR) PURPOSE Removes the specified directory. EXAMPLE MOV AX,SEG DName ;Directory name MOV DS,AX MOV DX,OFFSET DName MOV AH,3AH ;Function-Remove directory INT 21H ;Issue request to DOS JC Error DName DB "?? .. ??",0 ; ASCIIZ Name ; example: "c:\dir",0 COMMENTS On entry, DS:DX contains the address of an ASCIIZ string with the drive and directory path names. The specified directory is removed from the structure. The current directory or a directory with files in it cannot be removed. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. Network Access Rights: Requires Create access rights. 3BH -- CHANGE THE CURRENT DIRECTORY (CHDIR) PURPOSE Changes the current directory to the specified directory. EXAMPLE MOV AX,SEG DName ;Directory name MOV DS,AX MOV DX,OFFSET DName MOV AH,3BH ;Function -- Change directory INT 21H ;Issue request to DOS JC Error DName DB "?? .. ??",0 ; ASCIIZ Name ; example: "c:\dir",0 COMMENTS On entry, DS:DX contains the address of an ASCIIZ string with drive and directory path names. The string is limited to 64 characters and cannot contain a network path. If any member of the directory path does not exist, the directory path is not changed. Otherwise, the current directory is set to the ASCIIZ string. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. 3CH -- CREATE A FILE (CREAT) PURPOSE Creates a new file or shortens an old file to 0 length in preparation for writing. EXAMPLE MOV AX,SEG FName ;File name MOV DS,AX MOV DX,OFFSET FName MOV AH,3CH ;Function -- Create a File MOV CX,Attribute ; Attribute of the file ; Allowed values ; 0001H=Read only ; 0002H=Hidden ; 0004H=System ; 0008H=Volume label INT 21H ; Issue request to DOS JC Error ; Error code in AX MOV Handle,AX ; Save file handle for FName DB "?? .. ??",0 ; ASCIIZ Name ; example: "c:\dir\file.ext",0 Handle DW ? ; File handle Attribute DW ? ; Attributes for directory entry COMMENTS If the file did not exist, the file is created in the appropriate directory and the file is given the read/write access code. The file is opened for read/write, the read/write pointer is set to the first byte of the file and the handle is returned in AX. Note that function call 43H (Change File Mode) can be used later to change the file's attribute. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. This function does not replace an existing volume label. You must delete the existing volume label before issuing this call. Network Access Rights: Requires Create access rights. 3DH -- OPEN A FILE PURPOSE Opens the specified file. EXAMPLE MOV AX,SEG FName ; File name MOV DS,AX MOV DX,OFFSET FName MOV AH,3DH ; Function -- Open a File MOV AL,OpenMode INT 21H ; Issue request to DOS JC Error ; Error code in AX MOV Handle,AX ; Save file handle for following operations FName DB "?? .. ??",0 ; ASCIIZ Name ; example: "c:\dir\file.ext",0 Handle DW ? ; File Handle OpenMode DB ? ; Open mode COMMENTS The read/write pointer is set at the first byte of the file and the record size of the file is 1 byte. The read/write pointer can be changed with function call 42H. The returned file handle must be used for subsequent input and output to the file. The file's date and time can be obtained or set through call 57H, and its attribute can be obtained through call 43H. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. NOTES: 1. This call opens any normal or hidden file whose name matches the name specified. 2. Device names cannot end in a colon. 3. When a file is closed, any sharing restrictions placed on it by the open are canceled. 4. File sharing must be loaded, or the file must be a network file for the sharing modes to function. Refer to the SHARE command. 5. The file read-only attribute can be set when creating the file using extended FCBs or specifying the appropriate attribute in CX and using the CHMOD interrupt 21H function call or the DOS 4.00 ATTRIB command. 6. If the file is inherited by the subordinate process, all sharing and access restrictions are also inherited. 7. If an open file handle is duplicated by either of the DUP function calls, all sharing and access restrictions are also duplicated. OPEN MODE The open mode is defined in AL and consists of four bit-oriented fields: INHERITANCE FLAG Specifies if the opened file is inherited by a subordinate process. SHARING MODE FIELD Defines which operations other processes can perform on the file. RESERVED FIELD ACCESS FIELD Defines which operations the current process can perform on the file. BIT FIELDS The bit fields are mapped as follows: <I> < S > <R> < A > Open Mode bits 7 6 5 4 3 2 1 0 I Inheritance flag If I = 0; File is inherited by subordinate processes. If I = 1; File is private to the current process. S Sharing Mode The file is opened as follows: S = 000 -- Compatibility mode S = 001 -- DenyRead/Write mode (exclusive) S = 010 -- DenyWrite mode S = 011 -- DenyRead mode S = 100 -- DenyNone mode Any other combinations are invalid. When opening a file, you must inform DOS 4.00 which operations any other processes, in sharing mode, can perform on the file. The default, compatibility mode, denies all other computers in a network access to the file. If other processes can continue to read the file while your process is operating on it, specify DenyWrite. DenyWrite prohibits writing by other processes, but allows reading. Similarly, you must specify which operations, or access modes, your process can perform. The default access mode, ReadWrite, causes the open request to fail if another process on the computer or any other computer on a network has the file opened with any sharing mode other than DenyNone. If you intend to read from the file only, your Open will succeed unless all other processes have specified DenyNone or DenyWrite. File sharing requires cooperation of both sharing processes. R Reserved (set this bit field to 0). A Access The file access is assigned as follows: If A = 000; Read access If A = 001; Write access If A = 010; Read/Write access Any other combinations are invalid. Network Access Rights: If the Access field (A) of the Open mode field (AL) is equal to: 000 Requires Read access rights 001 Requires Write access rights 010 Requires Read/Write access rights COMPATIBILITY MODE A file is considered to be in compatibility mode if the file is opened by: Any of the CREATE function calls An FCB function call A handle function call with compatibility mode specified. A file can be opened any number of times in compatibility mode by a single process, provided that the file is not currently open under one of the other four sharing modes. If the file is marked read-only, and is open in DenyWrite sharing mode with Read Access, the file may be opened in Compatibility Mode with Read Access. If the file was successfully opened in one of the other sharing modes and an attempt is made to open the file again in Compatibility Mode, an interrupt 24H is generated to signal this error. The base interrupt 24H error indicates DRIVE NOT READY, and the extended error indicates a SHARING VIOLATION. SHARING MODES The sharing modes for a file opened in compatibility mode are changed by DOS 4.00 depending on the read-only attribute of the file. This allows sharing of read-only files. +---------------------------------------------------+ | READ-ONLY | | FILE OPENED BY ACCESS SHARING MODE | +---------------------------------------------------+ | FCB Read-Only DenyWrite | +---------------------------------------------------+ | Handle Read Read-Only DenyWrite | +---------------------------------------------------+ | Handle Write Error ----- | +---------------------------------------------------+ | Handle Error ----- | | Read/Write | +---------------------------------------------------+ +---------------------------------------------------+ | NOT READ-ONLY | | FILE OPENED BY ACCESS SHARING MODE | +---------------------------------------------------+ | FCB Read/Write Compatibility | +---------------------------------------------------+ | Handle Read Read Compatibility | +---------------------------------------------------+ | Handle Write Write Compatibility | +---------------------------------------------------+ | Handle Read/Write Compatibility | | Read/Write | +---------------------------------------------------+ DENYREAD/WRITE MODE (EXCLUSIVE) If a file is successfully opened in DenyRead/Write mode, access to the file is exclusive. A file currently open in this mode cannot be opened again in any sharing mode by any process (including the current process) until the file is closed. DENYWRITE MODE A file successfully opened in DenyWrite sharing mode, prevents any other write access opens to the file (A = 001 or 010) until the file is closed. An attempt to open a file in DenyWrite mode is unsuccessful if the file is open with a write access. DENYREAD MODE A file successfully opened in DenyRead sharing mode, prevents any other read sharing access opens to the file (A = 000 or 010) until the file is closed. An attempt to open a file in DenyRead sharing mode is unsuccessful if the file is open in Compatibility mode or with a read access. DENYNONE MODE A file successfully opened in DenyNone mode, places no restrictions on the read/write accessibility of the file. An attempt to open a file in DenyNone mode is unsuccessful if the file is open in Compatibility mode. When accessing files that reside on a network disk, no local buffering is done when files are opened in any of the following sharing modes: DenyRead DenyNone. Therefore, in a network environment, DenyRead/Write sharing mode, Compatibility sharing mode, and DenyWrite mode opens are buffered locally. The following sharing matrix shows the results of opening, and subsequently attempting to reopen the same file using all combinations of access and sharing modes: Y :2nd,3rd,...open is allowed N :2nd,3rd,...open is denied DRW :DenyRead/Write Mode (Exclusive) DW :DenyWrite Mode DR :DenyRead Mode ALL :Read/Write Mode I :Read Only Access O :Write Only Access IO :Read/Write Access 3EH -- CLOSE A FILE HANDLE PURPOSE Closes the specified file handle. EXAMPLE MOV AH,3EH ; Function Call -- ; Close a Handle MOV BX,Handle INT 21H ; Issue request to DOS JC Error ; Error code in AX Handle DW ? ; File Handle (from Open / Create) COMMENTS On entry, BX contains the file handle that was returned by Open or Create. On return, the file is closed, the directory is updated, and all internal buffers for that file are flushed. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. 3FH -- READ FROM A FILE OR DEVICE PURPOSE Transfers the specified number of bytes from a file into a buffer location. EXAMPLE MOV AX,SEG Buffer ; Address data buffer MOV DS,AX MOV DX,OFFSET Buffer MOV AH,3FH ; Function -- Read from a file MOV BX,Handle MOV CX,BufSize ; Buffer size INT 21H ; Issue request to DOS JC Error ; Error code in AX CMP AX,0 ; At End Of File? JE EOF ; Yes! MOV SizeRead,AX ; Save Amount Read N EQU 512 ; Typical buffer size Handle DW ? ; File Handle (from Open /Create) BufSize DW N ; Buffer Size, N is Buffer DB N DUP(?) ; Data Buffer SizeRead DW ? ; Amount of Data in Buffer COMMENTS On entry, BX contains the file handle. CX contains the number of bytes to read. DS:DX contains the buffer address. On return, AX contains the number of bytes read. This function call attempts to transfer (CX) bytes from a file into a buffer location. It is not guaranteed that all bytes will be read. For example, when DOS 4.00 reads from the keyboard, at most one line of text is transferred. If this read is performed from the standard input device, the input can be redirected. If the value in AX is 0, then the program has tried to read from the end of file. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. Network Access Rights: Requires Read access rights. 40H -- WRITE TO A FILE OR DEVICE PURPOSE Transfers the specified number of bytes from a buffer into a specified file. EXAMPLE MOV AX,SEG Buffer ;Data Buffer MOV DS,AX MOV DX,OFFSET Buffer MOV CX,BufSize MOV AH,40H ;Function-Write to a File MOV BX,Handle MOV DX,OFFSET Buffer INT 21H ; Issue request to DOS JC Error ; Error code in AX CMP AX,CX ; Disk Full? JB FullDisk ; Yes! N EQU 512 ; Typical buffer size Handle DW ? ; File Handle (from Open / Create) BufSize DW N ; Buffer Size Buffer DB N DUP(?) ; Data Buffer COMMENTS On entry, BX contains the file handle. CX contains the number of bytes to write. DS:DX contains the address of the data to write. This function call attempts to transfer (CX) bytes from a buffer into a file. AX returns the number of bytes actually written. If the carry flag is not set and this value is not the same as the number requested (in CX), it should be considered an error. Although no error code is returned, your program can compare these values. Normally, the reason for the error is a full disk. If this write is performed to the standard output device, the output can be redirected. To truncate a file at the current position of the file pointer, set the number of bytes (CX) to 0 before issuing the interrupt 21H. The file pointer can be moved to the desired position by reading, writing, and performing function call 42H, (Move File Read/Write Pointer.) If the file is read-only, the write to the file or device is not performed. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. Network Access Rights: Requires Write access rights. 41H -- DELETE A FILE FROM A SPECIFIED DIRECTORY (UNLINK) PURPOSE Removes a directory entry associated with a filename. EXAMPLE MOV AX,SEG FName ; File Name MOV DS,AX MOV DX,OFFSET FName MOV AH,41H ; Function-Delete a File INT 21H ; Issue request to DOS JC Error ; Error code in AX FName DB "?? .. ??",0 ; ASCIIZ Name ; example: "c:\dir\File.ext",0 COMMENTS Global filename characters are not allowed in any part of the ASCIIZ string. Read-only files cannot be deleted by this call. To delete a read-only file, you can first use call 43H to change the file's read-only attribute to 0, then delete the file. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. Network Access Rights: Requires Create access rights. 42H -- MOVE FILE READ WRITE POINTER (LSEEK) PURPOSE Moves the read/write pointer according to the method specified. EXAMPLE MOV AH,42H ; Function Call -- ; Move Read/Write Pointer MOV AL,Method ; Method of Positioning: ; 0 = From Beginning of File ; (BOF) ; 1 = From Current Position ; 2 = From End of File (EOF) MOV BX,Handle ; Select File MOV DX,WORD PTR Position+0 ; New Position = Position + METHOD MOV CX,WORD PTR Position+2 INT 21H ; Issue request to DOS JC Error ; Error code in AX MOV WORD PTR Position+0,AX ; Set new File Position MOV WORD PTR Position+2,DX Handle DW ? ; File Handle (from Open / ; Create) Position DD ? ; File Offset (may be ; negative) Method DB ? COMMENTS On entry, AL contains a method value. BX contains the file handle. CX:DX contains the desired offset in bytes with CX containing the most significant part. On return, DX:AX contains the new location of the pointer with DX containing the most significant part if the carry flag is not set. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. This function call moves the read/write pointer according to the following methods: +---------+-----------------------------------------------------------------+ | AL | DESCRIPTION | +---------+-----------------------------------------------------------------+ | 0 | The pointer is moved CX:DX bytes (offset) from the beginning of | | | the file. | +---------+-----------------------------------------------------------------+ | 1 | The pointer is moved to the current location plus offset. | +---------+-----------------------------------------------------------------+ | 2 | The pointer is moved to the end-of-file plus offset. This | | | method can be used to determine file's size. | +---------+-----------------------------------------------------------------+ NOTE: If an LSEEK operation is performed on a file that resides on a network disk that is open in either DenyRead or DenyNone sharing mode, the read/write pointer information is adjusted on the computer where the file actually exists. If the file is opened in any other sharing mode, the read/write pointer information is kept on the remote computer. 43H -- CHANGE FILE MODE (CHMOD) PURPOSE Changes the file mode of the specified file. EXAMPLE ; To Get Attributes MOV AX,SEG FName ;File Name MOV DS,AX MOV DX,OFFSET FName ;DS:DX points to ASCIIZ path name MOV AL,0 ;Indicate get MOV AH,43H ;Function-Change File Mode INT 21H ;Issue request to DOS JC Error ;Error code in AX MOV Attribute,CX ;Save Attribute ; To Set Attributes MOV AX,SEG FName ;File Name MOV DS,AX MOV DX,OFFSET FName ;DS:DX points to ASCIIZ path name MOV AL,1 ;Indicate set MOV AH,43H ;Function-Change File Mode MOV CX,Attribute ;Set Attribute INT 21H ;Issue request to DOS JC Error ;Error code in AX Fname DB 64 Dup (0) ;ASCIIZ Name ; example: "c:\dir\File.ext",0 Attribute DW ? ;File Attribute ; example: 0001H to set Read-Only COMMENTS On entry, AL contains a function code, and DS:DX contains the address of an ASCIIZ string with the drive, path, and filename. If AL contains 01H, the file's attribute is set to the attribute in CX. See "The Disk Directory" on page 2-3 for the attribute byte description. If AL is 00H the file's current attribute is returned in CX. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. NOTE: Only the Archive (20H), Read-Only (01H), System (04H) and Hidden (02H) bits can be changed. All other bits of CX must be 0, otherwise, an error may be indicated. Network Access Rights: To change the archive bit (AL=20H), no access rights are required. To change any other bit, Create access rights are required. 44H -- I/O CONTROL FOR DEVICES PURPOSE Sets or gets device information associated with open device handles, or sends control strings to the device handle or receives control strings from the device handle. See Appendix C for full details on this function call. 45H -- DUPLICATE A FILE HANDLE (DUP) PURPOSE Returns a new file handle for an open file that refers to the same file at the same position. EXAMPLE MOV AH,45H ; Function Call -- ; Duplicate a Handle MOV BX,Handle ; Select File INT 21H ; Issue request to DOS JC Error ; Error code in AX MOV NewHandle,AX ; Save New Handle Handle DW ? ; File Handle (from Open / Create) NewHandle DW ? ; File Handle that duplicates Handle COMMENTS On entry, BX contains the file handle. On return, AX contains the returned file handle. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. NOTE: If you move the read/write pointer of either handle by a read, write, or LSEEK function call, the pointer for the other handle is also changed. 46H -- FORCE A DUPLICATE OF A HANDLE (FORCDUP) PURPOSE Forces the handle in CX to refer to the same file at the same position as the handle in BX. EXAMPLE MOV AH,46H ; Function Call -- ; Force Duplicate a Handle MOV BX,Handle ; Select file MOV CX,NewHandle ; Select new definition of File INT 21H ; Issue request to DOS JC Error ; Error code in AX Handle DW ? ; File Handle (from Open/Create) NewHandle DW ? ; File Handle that duplicates Handle COMMENTS On entry, BX contains the file handle. CX contains a second file handle. On return, the CX file handle refers to the same file at the same position as the BX file handle. If the CX file handle was an open file, it is closed first. If you move the read/write pointer of either handle, the pointer for the other handle is also changed. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. 47H -- GET CURRENT DIRECTORY PURPOSE Places the full path name (starting from the root directory) of the current directory for the specified drive in the area pointed to by DS:SI. EXAMPLE MOV AX,SEG DName ; Directory Name Buffer MOV DS,AX MOV SI,OFFSET DName ; OS:SI points to buffer MOV DL,Drive ; Select Drive MOV AH,47H ; Function-Get Current Dir INT 21H ; Issue request to DOS JC Error ; Error code in AX Drive DB ? ; Drive (0=current, 1=A:, 2=b:, ...) DName DB 64 DUP(?) ; ASCIIZ Directory Name Returned ; example: "dir1\dir2",0 COMMENTS The drive letter is not part of the returned string. The string does not begin with a backslash and is terminated by a byte containing 00H. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. 48H -- ALLOCATE MEMORY Allocates the requested number of paragraphs of memory. EXAMPLE MOV AH,48H ; Function Call -- ; Allocate Memory MOV BX,Paragraphs ; Paragraphs Desired INT 21H ; Issue request to DOS JNC Done MOV AH,48H ; Function Call -- ; Allocate memory ; BX set to largest available memory INT 21H ; Issue request to DOS Done: MOV BlockSeg,AX ; Save BlockSeg of memory MOV Paragraphs,BX Paragraphs DW ? ; Size requested in paragraphs ; (Bytes allocated is 16 * Paragraphs) BlockSeg DW ? ; BlockSeg address of allocated memory COMMENTS On entry, BX contains the number of paragraphs requested. On return, AX:0 points to the allocated memory block. If the allocation fails, BX returns the size of the largest block of memory available in paragraphs. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. 49H -- FREE ALLOCATED MEMORY PURPOSE Frees the specified allocated memory. EXAMPLE MOV AH,49H ; Function Call -- Free Memory MOV ES,BlockSeg ; Set address to free INT 21H ; Issue request to DOS JC Error BlockSeg DW ? ; BlockSeg address of allocated memory COMMENTS On entry, ES contains the segment of the block to be returned to the system pool. On return, the block of memory is returned to the system pool. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. 4AH -- MODIFY ALLOCATED MEMORY BLOCKS (SETBLOCK) PURPOSE Modifies allocated memory blocks to contain the new specified block size. EXAMPLE MOV AH,4AH ; Function Call -- ; Modify Allocated Memory; allocate memory MOV ES,BlockSeg ; Set address to free MOV BX,BlockSize ; New size (may be larger or smaller) INT 21H ; Issue request to DOS JNC Done MOV AH,4AH ; Function Call -- ; Allocate memory ; BX set to largest available Size INT 21H ; Issue request to DOS Done: MOV Size,BX BlockSeg DW ? ; Segment address of allocated memory BlockSize DW ? ; Size requested in paragraphs ; (Bytes allocated is 16 * Size) COMMENTS Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. NOTE: This call is often used to set the size of a program before using function call 31H (Terminate Process and Remain Resident). Use the program segment prefix. This value can be obtained using function call 62H (Get Program Segment Prefix Address). Another use is to release memory to prepare for using function call 4BH (Load or Execute a Program). 4BH -- LOAD OR EXECUTE A PROGRAM (EXEC) PURPOSE Allows a program to load another program into memory and may choose to begin execution of it. EXAMPLE ; To Execute a Program MOV AH,4BH ; Function Call -- Execute a Program MOV AL,0 ; Indicate execute program MOV CX,SEG Parms ; Program parameters MOV ES,CX MOV BX,OFFSET Parms : ES:BX points to parameter block MOV CX,SEG PName ; Program name MOV DS,CX MOV DX,OFFSET PName ; DS:DX points to program name MOV WORD PTR StackSave+0,SP ; Save stack pointer MOV WORD PTR StackSave+2,SS INT 21H ; Issue request to DOS JC Error ; Error code in AX ; Note: All Registers (except CS:IP) Destroyed ; Program Runs here CLI ; Protect from stack usage MOV SS,WORD PTR StackSave+2 ; Restore stack pointer MOV SP,WORD PTR StackSave+0 STI ; Enable interrupts MOV AH,4DH ; Function Call -- Get Return Code INT 21H ; Issue request to DOS MOV RetCode,AX ; Save return code ; To Load an Overlay MOV AH,4BH ; Function Call -- Execute a Program MOV AL,3 ; Indicate load overlay MOV CX,SEG OParms ; Overlay parameters MOV ES,CX MOV BX,OFFSET OParms ; ES:BX points to parameter block MOV CX,SEG PName ; Overlay name MOV DS,CX MOV DX,OFFSET PName ; DS:DX points to overlay filename INT 21H ; Issue request to DOS JC Error ; Error code in AX PName DB 64 Dup (0) ; ASCIIZ Name ; example: "c:\dir\File.ext",0 Parms LABEL WORD ; Program parameters Env@ DW ? ; Environment segment address ; Value of 0000H indicates copy EXEC'ers ; Environment Cmd@ DD ? ; Command line address FCB1@ DD ? ; FCB Image to set to New PSP+5CH FCB2@ DD ? ; FCB Image to set to New PSP+6CH StackSave DD ? ; Stack pointer save area RetCode DW ? ; Program return code ; (see function code 4DH for more informatio OParms LABEL WORD ; Overlay parameters Load@ DW ? ; Overlay load segment address RelocFactor DW ? ; Relocation factor to apply (for .EXE files COMMENTS Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. Refer to "Responding to Errors" on page B-5 and "Extended Error Codes" on page B-5 for more information on the codes returned from function call 59H. The following function values are allowed in AL: +---------------------------------------------------------------------------+ | FUNCTION | | VALUE DESCRIPTION | +---------------------------------------------------------------------------+ | 00H Load and execute the program. A program segment prefix is | | established for the program; terminate and Ctrl-Break addresses | | are set to the instruction after the EXEC system call. | | | | NOTE: When control is returned, all registers are changed, | | including the stack. You must restore SS, SP, and any | | other required registers before proceeding. | +---------------------------------------------------------------------------+ | 03H Load, do not create the program segment prefix, and do not | | begin execution. This is useful in loading program overlays. | +---------------------------------------------------------------------------+ All open files of a process are duplicated in the newly created process after an EXEC, unless the file was opened with the inheritance bit set to 1. This means that the parent process has control over the meanings of standard input, output, auxiliary, and printer devices. The parent could, for example, write a series of records to a file, open the file as standard input, open a listing file as standard output, and then execute a sort program that takes its input from standard input and writes to standard output. Also inherited (or copied from the parent) is an "environment." This is a block of text strings (less than 32KB total) that conveys various configuration parameters. The following is the format of the environment (always on a paragraph boundary): +---------------------------------------------------------------------------+ | Byte ASCIIZ string 1 | +---------------------------------------------------------------------------+ | Byte ASCIIZ string 2 | +---------------------------------------------------------------------------+ | ... | +---------------------------------------------------------------------------+ | Byte ASCIIZ string n | +---------------------------------------------------------------------------+ | Byte of 0 | +---------------------------------------------------------------------------+ Typically the environment strings have the form: parameter=value Following the byte of 0 in the environment is a WORD that indicates the number of other strings following. Following this is a copy of the DS:DX filename passed to the child process. For example, the string VERIFY=ON could be passed. A 0 value of the environment address causes the newly created process to inherit the original environment unchanged. The segment address of the environment is placed at offset 2CH of the program segment prefix for the program being invoked. Errors codes are returned in AX. Refer to "Responding to Errors" on page B-5 and "Extended Error Codes" on page B-5 for more information on the codes returned. NOTE: When your program received control, all available memory was allocated to it. You must free some memory (see call 4AH) before EXEC can load the program you are invoking. Normally, you would shrink down to the minimum amount of memory you need, and free the rest. 4CH -- TERMINATE A PROCESS (EXIT) PURPOSE Terminates the current process and transfers control to the invoking process. EXAMPLE MOV AH,4CH ; Function Call -- Terminate a Process MOV AL,ErrorCode ; Set ERRORLEVEL INT 21H ; Issue request to DOS INT 20H ; Be safe if running on PC/DOS 1.1 ErrorCode DB ? ; Error Code (sets ERRORLEVEL if EXEC'ed ; by COMMAND.COM) COMMENTS In addition, a return code can be sent. The return code can be interrogated by the batch subcommands IF and ERRORLEVEL and by the wait function call 4DH. All files opened by this process are closed. 4DH -- GET RETURN CODE OF A SUBPROCESS (WAIT) PURPOSE Gets the return code specified by another process either through function call 4CH or function call 31H. It returns the Exit code only once. EXAMPLE MOV AH,4DH ; Function Call -- Get Return Code INT 21H ; Issue request to DOS MOV RetCode,AX ; Save return code RetCode LABEL WORD ; Program return code ExitCode DB ? ; ERRORLEVEL value ExitType DB ? ; Method used to exit: ; 00H -- for normal termination ; 01H -- for termination by Ctrl-Break ; 02H -- for termination as a result ; of a critical device error ; 03H -- for termination by call 31H COMMENTS The low byte of the exit code contains the information sent by the exiting routine. 4EH -- FIND FIRST MATCHING FILE (FIND FIRST) PURPOSE Finds the first filename that matches the specified file specification. EXAMPLE MOV AH,1AH ; Function Call -- Set DTA Address MOV CX,SEG DTA ; Address buffer for found file MOV DS,CX MOV DX,OFFSET DTA INT 21H ; Issue request to DOS MOV AH,4EH ; Function Call -- ASCIIZ Find First MOV CX,SEG FName ; Directory or filename MOV DS,CX MOV DX,OFFSET FName ; DS:DX points to ASCII filename MOV CX,Attribute ; Set Match Attribute INT 21H ; Issue request to DOS JC Error ; Error code in AX DTA LABEL BYTE ; Find return information DB 21 DUP(0) ; Reserved for DOS 4.00 to continu FileAttr DB ? ; Matched files attribute low byte FileTime DW ? ; File time FileDate DW ? ; File date FileSize DD ? ; File size FileNameExt DB "????????.???",0 ; Filename and extension FName DB 64 DUP (0) ; ASCIIZ Name ; example: "c:\dir\*.*",0 Attribute DW ? ; Select files attribute ; Combination of following: ; 0002H=Hidden ; 0004H=System ; 0008H=Volume label ; 0010H=Directory NOTES: If an extended FCB is used, the following search pattern is used: 1. If the attribute is 0, only normal file entries are found. Entries for volume label, sub-directories, hidden and system files are not returned. 2. If the attribute field is set for hidden or system files, or directory entries, it is to be considered as an inclusive search. All normal file entries plus all entries matching the specified attributes are returned. To look at all directory entries except the volume label, the attribute byte may be set to hidden + system + directory (all 3 bits on). 3. If the attribute field is set for the volume label, it is considered an exclusive search, and only the volume label entry is returned. COMMENTS The filename in DS:DX can contain global filename characters. The ASCIIZ string cannot contain a network path. See function call 11H (Search for First Entry) for a description of how the attribute bits are used for searches. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. Refer to "Responding to Errors" on page B-5 and "Extended Error Codes" on page B-5 for more information on the codes returned from function call 59H. NOTE: The name and extension of file found is returned as an ASCIIZ string. All blanks are removed from the name and extension, and, if an extension is present, it is preceded by a period. 4FH -- FIND NEXT MATCHING FILE (FIND NEXT) PURPOSE Finds the next directory entry matching the name that was specified on the previous Find First or Find Next function call. EXAMPLE MOV AH,1AH ; Function Call -- Set DTA Address MOV CX,SEG DTA ; Address buffer for found file MOV DS,CX MOV DX,OFFSET DTA INT 21H ; Issue request to DOS MOV AH,4FH ; Function Call -- Find next INT 21H ; Issue request to DOS JC Error ; Error code in AX DTA LABEL BYTE " ; Find Return Information DB 21 DUP(0) " ; Reserved for DOS to Continue Find " ; Set by Find First or Previous Fin FileAttr DB ? " ; Matched Files Attribute Low Byte FileTime DW ? " ; File Time FileDate DW ? " ; File Date FileSize DD ? " ; File Size FileNameExt DB "????????.???",0 ; File Name and Extension COMMENTS If a matching file is found, the DTA is set as described in call 4EH (Find First Matching File (FIND FIRST)). If no more matching files are found, an error code is returned. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. 54H -- GET VERIFY SETTING PURPOSE Returns the value of the verify flag. EXAMPLE MOV AH,54H ; Function Call -- Get VERIFY Setting INT 21H ; Issue request to DOS MOV VERIFY,AL ; Save VERIFY State VERIFY DB ? ; VERIFY State: ; 0 = OFF ; 1 = ON COMMENTS On return, AL returns 00H if verify is OFF, 01H if verify is ON. Note that the verify switch can be set through call 2EH (Set/Reset Verify Switch). 56H -- RENAME A FILE PURPOSE Renames the specified file. EXAMPLE MOV AH,56H ; Function Call -- ASCIIZ Rename File MOV CX,SEG FName ; File Name MOV DS,CX MOV DX,OFFSET FName ; DS:DX points to original name MOV CX,SEG NewName ; New File Name MOV ES,CX MOV DI,OFFSET NewName ; ES:DI points to rename INT 21H ; Issue request to DOS JC Error ; Error code in AX FName DB 64 DUP (0) ; ASCIIZ Name ; example: "c:\dir\abc.lst",0 NewName DB 64 DUP (0) ; ASCIIZ Name ; example: "\dir\xyz.lst",0 COMMENTS If a drive is used in the NewName string, it must be the same as the drive specified or implied in the Name string. The directory paths need not be the same, allowing a file to be moved to another directory and renamed in the process. Directory names can be changed but not moved. Global filename characters are not allowed in the filename. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. Refer to "Responding to Errors" on page B-5 and "Extended Error Codes" on page B-5 for more information on the codes returned from function call 59H. Network Access Rights: Requires Create access rights. 57H -- GET/SET FILE'S DATE AND TIME PURPOSE Gets or sets a file's date and time. EXAMPLE ; To Get a File's Date and Time MOV AH,57H ; Function Call -- Get/Set Date and Time MOV AL,0 ; Indicate get MOV BX,Handle ; Select file INT 21H ; Issue request to DOS JC Error ; Error code in AX MOV FileTime,CX ; Save Time MOV FileDate,DX ; Save Date ; To Set a File's Date and Time MOV AH,57H ; Function Call -- Get/Set Date and Time MOV AL,1 ; Indicate Set MOV BX,Handle ; Select file+ MOV CX,FileTime ; Set Time MOV DX,FileDate ; Set Date INT 21H ; Issue request to DOS JC Error ; Error code in AX Handle DW ? ; File Handle (from Open / Create) FileTime DW ? ; File Time FileDate DW ? ; File Date COMMENTS The date and time formats are the same as those for the directory entry described in Chapter 5 of this book. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. Refer to "Responding to Errors" on page B-5 and "Extended Error Codes" on page B-5 for more information on the codes returned from function call 59H. 59H -- GET EXTENDED ERROR PURPOSE Returns additional error information, such as the error class, location, and recommended action. EXAMPLE PUSH DX ; Save Registers PUSH SI PUSH DI PUSH ES PUSH DS MOV AH,59H ; Function Call -- Get Extended Error MOV BX,0 ; Version 0 information INT 21H ; Issue request to DOS POP DS ; Restore registers POP ES POP DI POP SI POP DX MOV ExtError,AX ; Save error code MOV ErrorClass,BH ; Save error class MOV ErrorAction,BL ; Save error action MOV ErrorLocation,CH; Save error location ExtError DW ? ; DOS extended error ErrorClass DB ? ; Class of error ErrorAction DB ? ; Suggested action ErrorLocation DB ? ; System area effected COMMENTS This function call returns the error class, location, and recommended action, in addition to the return code. Use this function call from: Interrupt 24H error handlers Interrupt 21H function calls that return an error in the carry bit FCB function calls that return FFH. On return, the registers contents of DX, SI, DI, ES, CL, and DS are destroyed. ERROR RETURN IN CARRY BIT For function calls that indicate an error by setting the carry flag, the correct method for performing function call 59H is: Load registers. Issue interrupt 21H. Continue operation, if carry not set. Disregard the error code and issue function call 59H to obtain additional information. Use the value in BL to determine the suggested action to take. ERROR STATUS IN AL For function calls that indicate an error by setting AL to FFH, the correct method for performing function call 59H is: Load registers. Issue interrupt 21H. Continue operation, if error is not reported in AL. Disregard the error code and issue function call 59H to obtain additional information. Use the value in BL to determine the suggested action to take. 5AH -- CREATE UNIQUE FILE PURPOSE Generates a unique filename, and creates that file in the specified directory. EXAMPLE MOV AH,5AH ; Function Call -- Create a ; Unique File MOV CX,SEG DirName ; Directory name MOV DS,CX MOV DX,OFFSET DirName MOV CX,Attribute ; File attribute INT 21H ; Issue request to DOS JC Error ; Error code in AX MOV Handle,AX ; Save file handle for following ; Operations DirName DB "?? .. ??\",0 ; ASCIIZ name DB "????????.???" ; example in : "c:\dir\",0 ; example out: "c:\dir\file",0 Handle DW ? ; File handle Attribute DW ? ; Select file's attribute COMMENTS On entry, AH contains 5AH. If no error has occurred, the file is opened in compatibility mode with Read/Write access. The read/write pointer is set at the first byte of the file and AX contains the file handle and the filename is appended to the path specified in DS:DX. This function call generates a unique name and attempts to create a new file in the specified directory. If the file already exists in the directory, then another unique name is generated and the process is repeated. Programs that need temporary files should use this function call to generate unique filenames. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. Refer to "Responding to Errors" on page B-5 and "Extended Error Codes" on page B-5 for more information on the codes returned from function call 59H. NOTE: The file created using this function call is not automatically deleted at program termination. Network Access Rights: Requires Create access rights. 5BH -- CREATE NEW FILE PURPOSE Creates a new file. EXAMPLE MOV AH,5BH ; Function Call -- Create a New File MOV CX,SEG FName ; File Name MOV DS,CX MOV DX,OFFSET FName MOV CX,Attribute INT 21H ; Issue request to DOS JC Error ; Error code in AX MOV Handle,AX ; Save File Handle for following operations FName DB 64 DUP (0) ; ASCIIZ Name ; example: "c:\dir\file",0 Handle DW ? ; File Handle Attribute DW ? ; Select File's Attribute COMMENTS This function call is the same as function call 3CH (Create), except it will fail if the filename already exists. The file is created in compatibility mode for reading and writing and the read/write pointer is set at the first byte of the file. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. Refer to "Responding to Errors" on page B-5 and "Extended Error Codes" on page B-5 for more information on the codes returned from function call 59H. Network Access Rights: Requires Create access rights. 5CH -- LOCK/UNLOCK FILE ACCESS PURPOSE Locks or unlocks a single range of bytes in an opened file. This function call provides database services that are useful in maintaining database integrity in a network environment. EXAMPLE ; To Lock a Single Range MOV AH,5CH ; Function Call -- ; Access Lock/Unlock File MOV AL,0 ; Indicate lock MOV BX,Handle ; Select file MOV DX,WORD PTR Position+0 ; Set position MOV CX,WORD PTR Position+2 MOV DI,WORD PTR Llength+0 ; Set length MOV SI,WORD PTR Llength+2 INT 21H ; Issue request to DOS JC Error ; Error code in AX ; To Unlock a Single Range MOV AH,5CH ; Function Call -- ; Lock/Unlock File Access MOV AL,1 ; Indicate unlock MOV BX,Handle ; Select file MOV DX,WORD PTR Position+0 ; Set position MOV CX,WORD PTR Position+2 MOV DI,WORD PTR Llength+0 ; Set length MOV SI,WORD PTR Llength+2 INT 21H ; Issue request to DOS JC Error ; Error code in AX Handle DW ? ; File Handle Position DD ? ; Start of Range Llength DD ? ; Length of Range COMMENTS The Lock/Unlock function calls should only be used when a file is opened using the DenyRead or DenyNone sharing modes. These modes do no local buffering of data when accessing files on a network disk. AL = 00H LOCK Provides a simple mechanism for excluding other processes' read/write access to regions of the file. If another process attempts to read or write in such a region, its system call is retried the number of times specified with the system retry count set by IOCTL. If, after those retries, no success occurs, a general failure error is generated, signaling the condition. The number of retries, as well as the length of time between retries, can be changed using function call 440BH (IOCTL Change Sharing Retry Count). The recommended action is to issue function call 59H (Get Extended Error) to get the error code, in addition to the error class, location, and recommended action. The locked regions can be anywhere in the logical file. Locking beyond end-of-file is not an error. It is expected that the time in which regions are locked will be short. Duplicating the handle duplicates access to the locked regions. Access to the locked regions is not duplicated across the EXEC system call. Exiting with a file open and having issued locks on that file has undefined results. Programs that may be cancelled using INT 23H (File Size) or INT 24H (Set Relative Record Field) should trap these and release the locks before exiting. The proper method for using locks is not to rely on being denied read or write access, but to attempt to lock the region desired and examining the error code. AL = 01H UNLOCK Unlock releases the lock issued in the lock system call. The region specified must be exactly the same as the region specified in the previous lock. Closing a file with locks still in force has undefined results. Exiting with a file open and having issued locks on that file has undefined results. Programs that may be aborted using INT 23H (File Size) or INT 24H (Set Relative Record Field) should trap these and release the lock before exiting. The proper method for using locks is not to rely on being denied read or write access, but attempting to lock the region desired and examining the error code. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. Refer to "Responding to Errors" on page B-5 and "Extended Error Codes" on page B-5 for more information on the codes returned from function call 59H. 5E00H -- GET MACHINE NAME PURPOSE Returns the character identifier of the local computer. EXAMPLE MOV AX,SEG CNAME ; Name buffer MOV DS,AX MOV DX OFFSET CNAME MOV AX,5E00H ; Function Call -- ; Get Machine Name INT 21H ; Issue request to DOS JC Error ; Error code in AX MOV NameFlag,CH ; Save name number indicator MOV NameID,CL ; Save NETBIOS name number CName DB "???????????????",0 ; ASCIIZ computer name NameFlag DB ? ; 0 = Name is not set ; 1 = Name is set NameID DB ? ; NETBIOS name number COMMENTS Get Machine Name returns the text of the current computer name to the caller. The computer name is a 15-character byte string padded with spaces and followed by a 00H byte. If the computer name was never set, register CH is returned with 00H and the value in the CL register is invalid. The IBM PC Local Area Network program must be loaded for the function call to execute properly. 5E02H -- SET PRINTER SETUP PURPOSE Specifies an initial string for printer files. EXAMPLE MOV AX,5E02H ; Function Call -- ; Set Printer Setup MOV BX,Index ; Redirection List Index MOV CX,size ; String size MOV SI,SEG String ; String Buffer MOV DS,SI MOV SI,OFFSET String INT 21H ; Issue request to DOS JC Error ; Error code in AX Index DW ? ; Redirection List Index Size DW N ; String size (Maximum 64) String DB N DUP(?) ; Printer Setup String COMMENTS The string specified is put in front of all files destined for a particular network printer. Set Printer Setup allows multiple users of a single printer to specify their own mode of operation for the printer. BX is set to the same index that is used in function call 5F02H (Get Redirection List Entry). An error code is returned if print redirection is paused or if the IBM PC Local Area Network program is not loaded. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. Refer to "Responding to Errors" on page B-5 and "Extended Error Codes" on page B-5 for more information on the codes returned from function call 59H. IMPORTANT: The redirection index value may change if function call 5F03H (Redirect Device) or function call 5F04H (Cancel Redirection) is issued between the time the redirection list is scanned and the function call 5E02H (Set Printer Setup) is issued. Therefore, we recommend that you issue Set Printer Setup immediately after you issue "Get Redirection List ." 5E03H -- GET PRINTER SETUP PURPOSE Returns the printer setup string for printer files. EXAMPLE MOV AX,5E03H ; Function Call -- ; Get Printer Setup MOV BX,Index ; Redirection List Index MOV CX,SEG String ; String Buffer MOV ES,CX MOV DI,OFFSET String INT 21H ; Issue request to DOS JC Error ; Error code in AX MOV Ssize, CX ; Save String size Index DW ? ; Redirection List Index Ssize DW ? ; String size String DB 64 DUP(?) ; Printer Setup String COMMENTS This function call returns the printer setup string which was specified using the function call 5E02H (Set Printer Setup). The setup string is attached to all files destined for a particular printer. The value in BX is set to the same index issued in function call 5F02H (Get Redirection List). Error code 1 (invalid function number) is returned if the IBM PC Local Area Network is not loaded. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. Refer to "Responding to Errors" on page B-5 and "Extended Error Codes" on page B-5 for more information on the codes returned from function call 59H. IMPORTANT: The redirection index value may change if function call 5F03H (Redirect Device) or function call 5F04H (Cancel Redirection) is issued between the time the redirection list is scanned and the function call 5E03H (Get Printer Setup) is issued. Therefore, we recommend that you issue "Get Printer Setup" immediately after you issue "Get Redirection List." 5F02H -- GET REDIRECTION LIST ENTRY PURPOSE Returns nonlocal network assignments. EXAMPLE MOV BX,0 ; Start at beginning of list Get_Loop: ; Get next entry MOV Index,BX ; Redirection list index MOV AX,5F02H ; Function Call -- ; Get redirection list entry MOV SI,SEG device ; "PRN" is possible MOV DS,SI MOV SI,OFFSET device ; DS:SI points to local name MOV DI,SEG info MOV ES,DI MOV DI,OFFSET inf ; ES:DI points to buffer address of netwo PUSH BX PUSH DX ; Save registers PUSH BP INT 21H ; Issue request to DOS POP BP ; Restore registers POP DX JC CheckEnd ; Error code in AX MOV Status,BH ; Save status MOV Type,BL ; Save type MOV UserParm,CX ; Save user parmameter POP BX INC BX ; Set to next entry JMP Get_Loop CheckEnd: POP BX ; Balance state CMP AX,18 ; End of list? JNE Error ; No! Index DW ? ; Redirection list index (0 based) Device DB 128 DUP(?) ; ASCIIZ device name ; example: "LPT1",0 ; "A:",0 Status DB ? ; Device status ; Bit 0=0 : Device is OK ; Bit 0=1 : Device in Error ; Bit 7-1 reserved UserParm DW ? ; User parameter Type DB ? ; Device type ; 3 = NET USE device ; 4 = NET USE drive Info DB 128 DUP(?) ; NET USE network path ; example: "\\MYNODE\CDRIVE",0 COMMENTS The Get Redirection List Entry function call returns the list of network redirections that were created through function call 5F03H (Redirect Device). Each call returns one redirection, so BX should be increased by one each time to step through the list. The contents of the list may change between calls. The end-of-list is detected by error code 18 (no more files). Error code 1 (invalid function number) is returned if the IBM PC Local Area Network program is not loaded. If either disk or print redirection is paused, the function is not effected. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. Refer to "Responding to Errors" on page B-5 and "Extended Error Codes" on page B-5 for more information on the codes returned from function call 59H. 5F03H -- REDIRECT DEVICE PURPOSE Causes a Redirector/Server connection to be made. EXAMPLE MOV AX,5F03H ; Function Call -- ; Redirect Device MOV SI,SEG Device ; Device Buffer MOV DS,SI MOV SI,OFFSET Device MOV DI,SEG Net Path info ; Information Buffer MOV ES,DI MOV DI,OFFSET Net Path MOV BL,Type ; Set Type MOV CX,UserParm ; Set User Parameter INT 21H ; Issue request to DOS JC Error ; Error code in AX Device DB "....",0 ; ASCIIZ Device Name ; example: "LPT1",0 ; "A:",0 UserParm DW ? ; User Parameter Type DB ? ; Device Type ; 3 = NET USE Device ; 4 = NET USE Drive Net Path DB 128 DUP(0) COMMENTS This call defines the current directories for the network and defines redirection of network printers. If BL = 03, the source specifies a printer, the destination specifies a network path, and the CX register has a word that DOS 4.00 maintains for the programmer. For compatibility with the IBM PC Local Area Network program, CX should be set to 0. Values other than 0 are reserved for the IBM PC Local Area Network program. This word may be retrieved through function call 5F02H (Get Redirection List). All output destined for the specified printer is buffered and sent to the remote printer spool for that device. The printers are redirected at the INT 17H level. The source string must be PRN , LPT1, LPT2, or LPT3 each ended with a 00H. The destination string must point to a network name string of the following form: [\\computername\¤shortname|printdevice‡] The destination string must be ended with a 00H. The ASCIIZ password (0 to 8 characters) for access to the remote device should immediately follow the network string. The password must end with a 00H. A null (0 length) password is considered to be no password. If BL = 4, the source specifies a drive letter and colon ending with 00H, the destination specifies a network path ending with 00H, and the CX register has a word that DOS maintains for the programmer. For compatibility with the IBM PC Local Area Network program, CX should be set to 00H. Values other than 00H are reserved for the IBM PC Local Area Network program. The value may be retrieved through function call 5F02H (Get Redirection List). If the source was a drive letter, the association is made between the drive letter and the network path. All subsequent references to the drive letter are translated to references to the network path. If the source is an empty string, the system attempts to grant access to the destination with the specified password without redirecting any device. The ASCIIZ password for access to the remote path should immediately follow the network string. A null (0 length) password ended with 00H is considered to be no password. Error codes are returned in AX. Issue function call 59H for additional information about the error class, suggested action, and location. Refer to "Responding to Errors" on page B-5 and "Extended Error Codes" on page B-5 for more information on the codes returned from function call 59H (Get Extended Error) . NOTES: 1. Devices redirected through this function call are not displayed by the NET USE command. 2. An error is returned if you try to redirect a drive while disk redirection is paused, or if you try to redirect a printer while print redirection is paused. 5F04H -- CANCEL REDIRECTION PURPOSE Cancels a previous redirection. EXAMPLE MOV AX,5F04H ; Function Call -- ; Cancel redirection MOV SI,SEG Device ; Device buffer MOV DS,SI MOV SI,OFFSET Device INT 21H ; Issue request to DOS JC Error ; Error code in AX Device DB "....",0 ; ASCIIZ Device Name ; example: "LPT1",0 ; "A:",0 ; "\\Computer\Path",0 COMMENTS The redirection created by the Redirect Device function call (5F03H) is removed through the Cancel Redirection call. If the buffer points to a drive letter and the drive is associated with a network name, the association is ended and the drive is restored to its physical meaning. If the buffer points to PRN, LPT1, LPT2, or LPT3, and the device has an association with a network device, the association is terminated and the device is restored to its physical meaning. If the buffer points to a network path ending with 00H and a password ending with 00H, the association between the local machine and the network directory is terminated. An error is returned if you try to cancel a redirected file device while disk redirection is paused, or if you try to cancel a redirected printer while print redirection is paused. Error code 1 (invalid function number) is returned if the IBM PC Local Area Network program is not loaded. Error codes are returned in AX. Issue function call 59H (Get Extended Error) for additional information about the error class, suggested action, and location. Refer to "Responding to Errors" on page B-5 and "Extended Error Codes" on page B-5 for more information on the codes returned from function call 59H. 62H -- GET PROGRAM SEGMENT PREFIX ADDRESS PURPOSE Returns the program prefix address. EXAMPLE MOV AH,62H ; Function Call -- ; Get Program Segment Prefix Address INT 21H ; Issue request to DOS JC Error ; Error code in AX MOV PSPSeg,BX ; Save PSP address PSPSeg DW ? ; Segment address of my PSP COMMENTS The internal PSP address for the currently executing process is returned in BX. 65H -- GET EXTENDED COUNTRY INFORMATION PURPOSE Returns extended country information. EXAMPLE ; To get information MOV AH,65H ; Function Call -- ; Get extended country information MOV AL,InfoID ; Data/function requested ; (1, 2, 4, 6 or 7). MOV BX,CodePage ; Set desired code page ; (-1=current, Set by function call 6602H). MOV CX,SizeBuffer ; Maximum data to return ; (must be >= 5) MOV DX,CountryID ; Set desired Country ID ; (-1=current, set by function call 38H). MOV DI,SEG Buffer ; Information return buffer MOV DS,DI MOV DI,OFFSET Buffer INT 21H ; Issue request to DOS JC Error ; Error code in AX Buffer LABEL BYTE ; Format depends on AL value ; AL=1 : Extended Country Information SizeBuffer DW ? ; Size of data block to return InfoID DB ? ; Type of info to get CIinfoSize DW ? ; amount of data that follows ; (limited by CX input) CountryID DW ? ; Selected CountryID CodePage DW ? ; Selected Code Page ; See function call 38H for the format of the remainder of this buffer ; AL=2 : Upper Case Table DB 2 ; Indicates Upper Case Table UpperCase@ DD ? ; Address of Upper Case Table ; AL=4 : File Upper Case Table DB 4 ; Indicates File Upper Case Table UpperCase@ DD ? ; Address of File Upper Case Table ; AL=6 : Collating Table DB 6 ; Indicates Collate Table Collate@ DD ? ; Address of Collate Table ; AL=7 : DBCS Vector Table DB 7 ; Indicates DBCS Vector Table DBCS@ DD ? ; Address of DBCS Vector Table COMMENTS On entry, DX contains the ID of the country for which the extended information is needed. AL contains the ID value for the country. If the country code and code page do not match, or if either one or both are invalid, an error code of 2 (file not found) is returned in AX. The size requested in CX must be 5 or greater. If it is less than 5, an error code of 1 is returned in AX. If the amount of information returned is greater than the size requested in CX, it is ended and no error is returned in AX. NOTE: For further information on the country information, see function call 38H (Get or Set Country Dependent Information). The NLSFUNC DOS extension must be installed to get information for countries other than the Current Country. The uppercase table and the filename uppercase tables are 130 bytes long, consisting of a length field (2 bytes), followed by 128 uppercase values for the upper 128 ASCII characters. They have the following layout: Tsize DW 128 ; Table Size Table DB 128 DUP(?) ; Upper case versions of 80H to FFH The following formula can be used to determine the address of an uppercase equivalent for a lowercase character (ASCII in) in the uppercase table or the filename uppercase table. EXAMPLE ASCII in -(256-table len)+table start= address of ASCII out WHERE ASCII in = character to be generated table len = length of list of uppercase values (2 bytes) table start = starting address of uppercase table (4 bytes) ASCII out = uppercase value for ASCII in If the value of ASCII in is equal to or greater than (256-table len), there is an uppercase equivalent for ASCII in in the table. If it is lower than (256-table len), no uppercase equivalent exists in the table. The collate table is 258 bytes long, consisting of a length field (2 bytes) followed by 256 ASCII values, in the appropriate order. It has the following layout: Tsize DW 256 ; Table Size Table DB 256 DUP(?) ; Sort Weights for 00H to FFH The DBCS vector is variable in length, consisting of a length field (two bytes) followed by one or more pairs of bytes. It has the following layout: Tsize DW Nx2 ;List size 1 DB Start,end ;DBCS vector 1 2 DB Start,end ;DBCS vector 2 : N DB Start,end ;DBCS vector n DB 0,0 ;End marker 66H -- GET/SET GLOBAL CODE PAGE PURPOSE This function gets or sets the code page for the current country. MOV AX,6601H ; Function Call -- ; Get Global Code Page INT 21H ; Issue request to DOS JC Error ; Error code in AX MOV GlobalCP,BX ; Save Global Code Page MOV SystemCP,DX ; Save DOS System Code Page or MOV AX,6602H ; Function Call -- ; Set Global Code Page MOV BX,GlobalCP ; New Global Code Page INT 21H ; Issue request to DOS JC Error ; Error code in AX GlobalCP DW ? ; Current Code Page of DOS Country Informati SystemCP DW ? ; Code Page of DOS messages ; Often the default Code Page for the ; current country COMMENTS DOS 4.00 moves the new code page data from the COUNTRY.SYS file to a resident country buffer area. DOS 4.00 uses the new code page to perform a Select to all attached devices that are set up for code page switching, (that is, have a code page switching device driver specified in CONFIG.SYS). If any device fails to be selected, an error code of 65 is returned in AX. The code page must be recognizable by the current country, and DOS 4.00 must be able to open and read from the country information file. Otherwise, the carry flag will be set on return and AX will contain 02 (file not found). NOTE: NLSFUNC must be installed to use this function call, and all the devices must be prepared in order for the Select function to be successful. 67H -- SET HANDLE COUNT PURPOSE Permits more than 20 open files per process. EXAMPLE EntryPoint: MOV AH,62H ; Function Call -- ; Get PSP Address INT 21H ; Issue request to DOS JC Error ; Error code in AX MOV ES,BX ; Set Segment MOV AH,4AH ; Function Call -- ; Set Memory Block Size MOV BX,paragraphs ; Set Size INT 21H ; Issue request to DOS JC Error ; Error code in AX MOV AH,67H ; Function Call - Set Handle Count MOV BX,NewHandles ; Set new handle count INT 21H ; Issue request to DOS JC Error ; Error code in AX NewHandles DW ? ; Number of Handles need ; by this DOS 4.00 proce ListSize EQU (Endofprogram - EntryPoint) ; Number of bytes Paragraphs EQU (ListSize / 10H) ; Number of paragraphs End_of_program LABEL BYTE ; Last used position for ; this program COMMENTS The maximum number of file handles allowed for this interrupt is 64KB. If the the specified number of allowable handles is less than the current number allowed, the specified number will become current only after all the handles above the specified number have been closed. If the specified number is less than 20, the number is assumed to be 20. Data base applications can use this function to reduce the need to swap handles. You must release memory for DOS 4.00 to contain the extended handle list. You can do this by using the SET BLOCK (4AH) function call. 68H -- COMMIT FILE PURPOSE Causes all buffered data for a file to be written to the device. This function can be used instead of a close-open sequence. EXAMPLE MOV AH,68H ; Function Call -- Commit File MOV BX,Handle ; Select file INT 21H ; Issue request to DOS JC Error ; Error code in AX Handle DW ? ; Handle from previous Open or Create COMMENTS Commit File provides a faster and more secure method of committing data in multi-user environments such as the IBM PC Local Area Network. 6CH -- EXTENDED OPEN/CREATE PURPOSE Optionally opens and creates a file. EXAMPLE MOV AH,6CH ; Extended open MOV AL,0 ; Reserved MOV BX,MODE ; Open mode ; Format : 0WF00000ISSS0AAA ; AAA=Access code 0=Read ; 1=Write ; 2=Read/Write ; SSS=Sharing mode 0=Compatibility ; 1=DenyRead/Write ; 2=DenyWrite ; 3=DenyRead ; 4=DenyNone ; I 0=Pass handle to chile, 1=No inherit ; F 0=INT 24H, 1=Return error ; on this open and any I/O to this handle ; W 0=No commit, 1=Auto-Commit on write MOV CX,ATTR ; Create attribute (ignored if open) MOV DX,FLAG ; Function control, Format=0000000NNNNEEEE ; NNNN=Does not exist action ; 0=Fail, 1=Create ; EEEE=Exists action ; 0=Fail, 1=open, 2=Replace/Open MOV SI,SEG file name ; Name to open or create MOV DS,SI MOV SI,OFFSET file name INT 21H JC ERROR ; AX=Handle ; CX=Action taken code ; 1=File opened ; 2=File created/opened ; 3=File replaced/opened ;---- Mode DW ? ; Open mode bit ; Definitions Attr DW ? ; File attributes Flag DW ? ; Function definition File name 64 DUP (0) COMMENTS Function 6CH combines the functions currently available with OPEN, CREATE and a CREATE NEW. If F is 1, the critical error handler (Interrupt 24) is disabled for the handle returned by Extended Open. Any I/O issued to this handle will never generate the critical error but only the extended error. If F is 0, no actions are taken. If W is 1, any disk write using the handle returned by Extended Open will accompany with a commit call (see Interrupt 21H (AL=68H)). If W is 0, no actions are taken.