SIO User's Manual

By Ray Gwinn
 * Date: January 1, 1997

Introduction
SIO.SYS and VSIO.SYS are companion device drivers for Version 2 (and up) of the OS/2 operating system.

Both drivers (SIO/VSIO) have been coded with performance in mind, possibly sacrificing some compatibility. For this reason, SIO and VSIO are not exact replacements for the OS/2 drivers COM and VCOM. However, all serial communications programs tested by the author work correctly using SIO/VSIO.

This manual is intended for the SIO user. A separate SIO Technical Reference Manual‎ is available. The Technical Reference Manual also documents some advanced options and features that are not documented here.

This manual and the software distributed with it is provided with no guarantees. Use it at your own risk.

What is SIO
SIO is a Serial Input/Output (SIO) communications driver. It provides an interface between application programs and the serial communications hardware.

SIO had been designed as a high performance replacement for the OS/2 device driver COM.SYS. See the Technical Reference Manual for information about the known differences between COM.SYS and SIO.SYS.

SIO works with 8250 (type) serial I/O devices. Such devices include, but are not limited to the 8250A, 16450, 16550, 16550A and the 82510. If you have a PC that is an IBM or near compatible which has a serial communication port, it is likely that it contains one of these devices. In addition, SIO supports some intelligent serial I/O cards. See "Intelligent Cards Supported" for additional information. SIO will identify the type of serial devices that it finds and display them at load time.

Like other Device Drivers, SIO will do very little standing alone. There must be an application(s) program that makes use of SIO's functions before one will benefit from SIO.

What is VSIO
VSIO is a Virtual Device Driver (VDD). Virtual device drivers provide services for DOS programs executing under OS/2. Most Virtual Device Drivers emulate a specific hardware device and/or BIOS service. The primary job of a Virtual Device Driver is to convert misbehaved DOS input/output into well behaved input/output that can be accepted by the OS/2 driver SIO.SYS.

Using the protection mechanism of the 386 (and up) processor, a Virtual Device Driver can instruct OS/2 to trap all input/output for given hardware ports. Once trapped, the Virtual Device Driver (VDD) appropriately routes information to/from the Physical Device Driver (PDD) and to/from the DOS program.

VSIO creates a virtual (imaginary) 16550A or 16450 (UART) in software. Additionally VSIO emulates the BIOS INT 14h services. All of the hardware registers of the virtual UART are simulated by VSIO. VSIO does not attempt to simulate the timing of the real UARTs. DOS programs that depend on the timing of real hardware UARTs may have problems executing under VSIO.

All DOS programs that execute under VSIO should have RTS/CTS handshaking enabled (in the application) even if SIO proper is not using RTS/CTS handshake.

The virtualization (simulation) provided by VSIO is not (and can not be) exact. However, most well written DOS programs should not have problems.

VSIO will only work with SIO installed and the versions of SIO/VSIO must match. If VSIO refuses to install, you most likely have a version mismatch or COM.SYS is still installed. VSIO will not work with any other device driver like COM.SYS.

Installing SIO/VSIO
SIO is distributed as a ZIP file. To extract the individual files from the distribution file you need the program PKUNZIP or an equivalent. PKUNZIP is a product of PKWARE and can be downloaded from almost any bulletin board system (BBS). You probably already have PKUNZIP and know how to use it, otherwise I doubt that you would be reading this. When PKUNZIP is used to extract the various files, -AV should appear after each file name as it is extracted. In addition, the message: Authentic files Verified! should appear after the extraction process. If this message does not appear, or appears with a name other than Raymond L. Gwinn, the file is not an original SIO distribution file.

The only file that the basic user actually needs is SIO.SYS. Virtual DOS machine (VDM) users will also want VSIO.SYS. Copy one or both of these files to a convenient directory or subdirectory on your system. An installation program (INSTALL.EXE) is provided to install the SIO files and modify your CONFIG.SYS

Quick Start
Create a temporary directory, change into that directory and unzip the SIO distribution zip there. Type INSTALL followed by the enter key. For a basic setup, that is all that is needed.

If you choose to install SIO manually, the following should be done.

BE SURE THAT ANY SERIAL MOUSE DRIVER APPEARS IN THE CONFIG.SYS BEFORE SIO.SYS

If you are going to use standard communications ports, either COM1 or COM2 on an ISA bus (AT or clone), or COM1 through COM4 on a PS/2, then add the following line to your CONFIG.SYS file: DEVICE=SIO.SYS DEVICE=VSIO.SYS Be sure to REMark out the COM.SYS and VCOM.SYS device drivers if they exist in your CONFIG.SYS.

With the above statements you will be able to use standard COM1 and/or COM2 (if they exist) on any PC system known to the author.

If your setup is more complex, you must read on.

Command Line Options
The command line options are included in the command line that loads SIO in the CONFIG.SYS file. VSIO has no command line options. Command line options are usually grouped by port within parenthesis.

If you use only COM1 and/or COM2, at the standard IRQ and port addresses, you will not need any command line options. However, up to four serial communications ports, COM1 thru COM4, can be specified at any base port address and any IRQ. On PS/2 systems and some ISA cards, SIO/VSIO supports multiple communications devices sharing the same IRQ.

The basic command line syntax is as follows: DEVICE=SIO.SYS (Cn, An, In, Ig, Fc) [(Cn, An, In, Ig, Fc)] Where
 * "Cn":is the comm port number (1 thru 4) or the string COM1 thru COMn. The port number may preceeded by an asterisk "*" to indicate that the port may be used as a PCMCIA comm port (eg *1 or *COM1). Note that it is normal for SIO to display a warning about not finding anything at PCMCIA ports.
 * "An":is a hexadecimal number that defines the base hardware I/O port address for the communications port. If this field is left blank, the default I/O port address is used for the comm port. Note that default I/O addresses exist only for COM1 through COM4 on AT type systems and for COM1 through COM8 on PS/2 systems.
 * "In":is an IRQ number (0 thru 15) or the string IRQ0 thru IRQ15 or the string NONE. It is best if one leaves this field blank and allows SIO to determine the IRQ, see AUTOMATIC IRQ ASSIGNMENT below. The IRQ choice of NONE is provided for cards that can work either with or without an IRQ like the Hayes ESP.
 * "Ig":is an ignored parameter. If exists for compatibility with COM.SYS.
 * "Fc":is the Forced 16550A chip parameter. If an F is placed in this position, a 16550A UART chip type is forced regardless of the automatically detected chip type.

For a PC with COM1 and COM2 of standard configuration, the following command line will load SIO correctly: DEVICE=SIO.SYS (1, 3F8, 4) (2, 2f8, 3) A more readable, but identical, command line is: DEVICE=SIO.SYS (COM1,3F8,IRQ4) (COM2,2F8,IRQ3) Forcing a 16550A on COM1 would be as follows: DEVICE=SIO.SYS (COM1,3F8,IRQ4,,F) (COM2,2F8,IRQ3) In a similar manner, up to sixteen serial communications ports (four in the Shareware version) can be defined and supported by SIO and VSIO.

The Poor Man's Line Monitor (PMLM.EXE)
PMLM is basically of interest to developers of comm applications and those providing technical support for those applications. This SIO utility is released largely (in self defense) in the hope that some users can diagnose their own problems. PMLM's feature of saving trace information to disk will only work with registered and beta versions of SIO.

PMLM provides basic line monitoring for OS/2, DOS and Windows comm programs. All characters sent or received by application programs are displayed in the upper portion of the screen. Receive characters are displayed as "white on blue" and transmitted characters are displayed "yellow on violet". Line signals, such as CTS are displayed as "dim white on red" when turned off and "bright white on red" when turned on. In addition, a signal's transition to OFF is displayed in lower case and a signal's transition to ON is displayed in upper case.

Status information is displayed in the lower part of the screen. A bright white display means the signal is on, a dim white indicates that the signal is off. In addition, when bright, Rxoff and Txoff indicate the SIO has sent (Txoff) or received (Rxoff) an Xoff, and an Xon is pending.

When a DOS or Windows session uses a comm port, an additional line of signal status appears. This status line shows the state of the virtual UART's signals. Only the signals which MAY be different from the real UART's signals are shown.

"Rx Chars" and "Tx Chars" reflects the number of characters in SIO's receive and transmit buffers respectively.

The last line on the screen shows the keys (from the keyboard) that PMLM will recognize. The bright character shows the key to hit for the associated function. The font keys will not work in a windowed OS/2 session.

PMLM's command line requires one parameter, the comm port number, and optionally accepts an additional parameter giving a save trace file name. For example, PMLM 1 COM1INFO.TRC will monitor COM1 and save ALL of the communications traffic in the file COM1INFO.TRC. The trace files created by PMLM contain exactly the same information that is displayed by PMLM, video attributes and all.

VIEWPMLM.EXE
VIEWPMLM.EXE may be used to view trace files created by PMLM. VIEWPMLM.EXE requires one parameter, the trace file name. The user can use the keys UP, DOWN, PAGEUP, PAGEDOWN, HOME, and END to navigate the saved trace file. Registered SIO users may send VIEWPMLM.EXE (along with saved trace files) to anyone for technical support purposes.

VIEWPMLM can be used in native DOS, in DOS sessions under OS/2, and in OS/2 sessions. This means that even those developers and support people need not have OS/2 to view the captured communications data created by PMLM.

SIO's Utility (SU.EXE)
This utility program has several useful commands. You can obtain a list of the available commands by typing SU at any command line prompt without any parameters. One very useful command is SU IRQS. This command will show IRQs that are currently free for use. Commands are provided allowing user control (missing from MODE) are available. Status commands provide a wealth of diagnostic information.

Hayes ESP
The original ESP (ESP V1) is not supported. The SIO command line must contain the ESP's enhanced I/O port address. For bit rates exceeding 180000bps the IRQ MUST be specified for the master port. For lower data rates NONE may be specified for the IRQ. SIO does not search for the ESP ports as the Hayes drivers do under DOS/Windows. This searching can (will) break things under OS/2. The SIO command line for an ESP at I/O port 180h using IRQ14 would be as follows: DEVICE=path\SIO.SYS (COM1,180,IRQ14) (COM2,188,NONE) If you would like the above reflected to DOS sessions as a standard COM1 and COM2, then use the following command line: DEVICE=path\SIO.SYS (COM1,180:3F8,IRQ14:IRQ4) (COM2,188:2F8,NONE:IRQ3) Note that the numbers after the colons ":" are the address and IRQ of where the port appears to DOS software running under OS/2. Any IRQ specified for an ESP slave port is ignored. For those that like to have a clean looking CONFIG.SYS, SIO will accept NONE as the IRQ specification of an ESP slave port.

If you wish to use the ESP in Compatibility Mode, simply specify the base port address that the ESP's compatibility mode is configured for (ie 3F8 when configured for COM1).

Telcor Tport
The Telcor Tport is supported in both burst mode and 16450 emulation mode. When in burst mode, the Tport's 16k FIFOs are enabled. Additionally in burst mode, no IRQ is used by the Tport. In burst mode, any IRQ specified for the Tport is ignored. For those that like to have a clean looking CONFIG.SYS, SIO will accept NONE as the IRQ specification of a Tport. An example command line defining a Tport card to be used in burst mode; and that is configured for COM1 follows: DEVICE=path\SIO.SYS (COM1,Tport@3F8,NONE:IRQ4) The Tport's 16450 Emulation mode simply uses a normal SIO command line. e.g.: DEVICE=path\SIO.SYS (COM1,3F8,IRQ4:IRQ4) In both examples the "IRQ4" following the colon above, means that the virtual IRQs are to be sent to a VDM on IRQ4.

Automatic IRQ Assignment
SIO will automatically locate the IRQ that a comm port is attached to. The IRQ used by SIO for a given comm port is assigned in the following manner:

1 - If an IRQ is specified in the SIO command line then that IRQ is used. However, SIO will display a warning message if the IRQ seems to be other than specified.

2 - If no IRQ is specified in the command line, and if SIO detected the IRQ then the detected IRQ is used.

3 - If no IRQ is specified in the command, and if SIO could NOT detect an IRQ then the default IRQ for the comm port is used. SIO will also display a warning message in this case.

The following STYLE command line is recommended for all but the most unusual systems. That is, specify only the port number for those above COM2 (to tell SIO to support those ports) and let SIO do the rest. DEVICE=SIO.SYS (COM3) (COM4) If you do not have a COM3 or COM4, or if the mouse is using the only comm port above COM2 then the following command line should be used. DEVICE=SIO.SYS

DOS SETTINGS
VSIO gets its operational characteristics from DOS Settings. Several basic DOS Settings are provided. They specify the type of access (if any) that a DOS program is to have to a communication port that SIO controls.

All of the DOS Settings default to what most users should use most of the time (which is ON). Also, all of the DOS Settings are prefixed with SIO_.

If any of the DOS settings are changed, then the DOS session must be restarted from the Work Place Shell for the changed setting to take affect.

The provided DOS Settings and their meaning follow:

(where n is 1 thru 4). This DOS setting defaults to ON. If this setting is turned OFF for any or all of the ports, the DOS program will not be allowed any access to that port(s). This Dos setting defaults to ON and it applies to all communications ports used by the DOS session. When ON, this DOS setting means VSIO is to act as an interface between the SIO and the DOS program. When OFF, the DOS program is given direct access to the hardware ports of the UART(s). This DOS setting defaults to ON and it applies to all communications ports used by the DOS session. When ON, VSIO will simulate a 16550A. When OFF, VSIO will simulate a 16450. Some DOS programs may not work when a 16550A is simulated. Turning this setting off may allow the program to work (but slower). This DOS setting defaults to ON and it applies to all communications ports used by the DOS session. When ON, SIO will allow an OS/2 session to access a communications port which the DOS session first opened (and has not closed). If set to OFF, then the DOS session will have exclusive use of the communications port(s) that it uses.
 * "SIO_Allow_Access_COMn"
 * "SIO_Virtualize_COM_Ports"
 * "SIO_Virtualize_16550A"
 * "SIO_Share_Access_With_OS/2"

This setting does not apply to a second DOS session attempting to access a communications port, two different DOS sessions are never allowed to access the same port at the same time. Additionally, this setting has no affect upon the access to a communications port which is first opened by an OS/2 session.

DOS setting. This DOS setting defaults to off and it applies to all communications ports used by the DOS session. Some DOS BBS programs (such as Wildcat) and many DOS Door programs attempt to synchronize the screen output with transmitted data. This plays havoc with a multi tasking system like OS/2 and results in very slow transmitted data. When this setting is on, an attempt is made to fake out these misbehaved programs and allow them to run at normal transmit speed. This setting should not be turned on unless you experience VERY slow transmission from a DOS program.
 * "SIO_Screen_Sync_Kludge"

All of the DOS Settings that begin with "SIO_Mode" allows one to construct a MODE command for a DOS session. These settings apply to SIO proper, and not necessarily to the DOS program itself. For example, if you set XON/XOFF handshake with the appropriate SIO_Mode setting, you are specifying that SIO is to implement the handshaking. The DOS application itself will be unaware of this handshaking. This can be very confusing, so think it through before you start changing the defaults.

The "SIO_Mode" settings WILL NOT BE APPLIED IF THE COMM PORT IS ALREADY OPEN WHEN THE DOS SESSION FIRST ACCESSES THE COMM PORT. This means that the "SIO_Mode" settings will NOT be asserted for spawned DOS comm programs. That is, for spawned DOS comm programs, the mode of operation that is already in effect will continue to be in effect and the "SIO_Mode" settings are ignored.

This setting has three options that specify how SIO and VSIO are to treat the DTR signal. The there available option are: If either of the first two settings is selected, then basically the DOS application has direct control over the DTR signal. If the second option is selected, then DTR will be turned on by SIO when the DOS program first touches the comm port.
 * "SIO_Mode_DTR"
 * No Change at OPEN or CLOSE.
 * Turn ON at OPEN, OFF at CLOSE.
 * HandShake Signal, as in DTR/DSR.

If the third option is selected, then SIO will use DTR as a handshaking signal. That is, DTR will be turned off if SIO can not accept any further receive data. In addition, if the DOS application program turns off the Virtual DTR, VSIO will stop supplying the DOS application with receive data.

This setting specifies how SIO is to react to received data and the DSR signal. The two available options are: Ignore DSR During Receive. Required for Valid Receive Data.
 * "SIO_Mode_IDSR"

If the first option (the default) is selected, then SIO will ignore DSR and accept all received data. If the second option is selected, then SIO will ignore received data when the DSR signal is off. VSIO ignores this DOS setting.

This setting specifies how SIO will react to the CTS signal when transmitting data. The two available options are:
 * "SIO_Mode_OCTS"
 * HandShake Signal, as in RTS/CTS.
 * Ignore CTS During Transmit.

If the first option (the default) is selected, then SIO will not transmit data when the CTS signal is off. If the second option is selected, then SIO will ignore CTS during transmit. Note that this setting should be set to "Ignore" for 3 wire connections like the Seiko Smart Label Printer, and Laplink. VSIO ignores this setting.

This setting specifies how SIO is to react to the DSR signal during transmit. The two available options are:
 * "SIO_Mode_ODSR"
 * Ignore DSR During Transmit.
 * HandShake Signal, as in DTR/DSR.

If the first option (the default) is selected, then SIO will ignore DSR during transmit. If the second option is selected, then SIO will not transmit data when the DSR signal is off. VSIO ignores this setting.

This setting has three options that specify how SIO and VSIO are to treat the RTS signal. The there available option are: If either of the last two settings is selected, then basically the DOS application has direct control over the RTS signal. If the last option is selected, then RTS will be turned on by SIO when the DOS program first touches the comm port.
 * "SIO_Mode_RTS"
 * HandShake Signal, as in RTS/CTS.
 * No Change at OPEN or CLOSE.
 * Turn ON at OPEN, OFF at CLOSE.

If the first option (the default) is selected, then SIO will use RTS as a handshaking signal. That is, RTS will be turned off if SIO can not accept any further receive data. In addition, if the DOS application program turns off the virtual RTS signal, VSIO will stop supplying the DOS application with receive data.

This setting specifies if (and how) SIO is to use XON/XOFF flow control. The four options are: The first option (the default) specifies that SIO is not to use XON/XOFF flow control at all. The second option specifies that SIO is to treat received XON/XOFF as flow control, but that SIO must not send XON/XOFF as flow control characters. The third option specifies that SIO may send XON/XOFF as flow control characters, but that received XON/XOFF characters are to be treated as normal data. The fourth option turns on XON/XOFF flow control in both directions, meaning that all sent and received XON/XOFF characters are flow control.
 * "SIO_Mode_XON/XOFF"
 * No XON/XOFF flow control by SIO.
 * Received XON is flow control.
 * Sent XON is flow control.
 * Rcvd and Sent XON is flow control.

This setting specifies how many characters that SIO will load into a 16550A UART at one time. The choices are 1 and 16 (16 is the default). The only case known to the author where one would select a setting of 1, is when very fast reaction to flow control is needed. One such case is the Seiko Smart Label Printer which uses XON/XOFF flow control and a 3 wire connection. If one is using a 16550 with a load count of 16, then 16 additional characters may be sent after an XOFF is received. This condition will overrun the Seiko Printer. If the "Load Count" is set to 1, then SIO will transmit (at most) two additional characters following a received XOFF which allows the Seiko Printer to work. A setting of 1 will cause additional system overhead due to additional transmit interrupts.
 * "SIO_Mode_FIFO_Load_Count"

Configuration Profiles
I will attempt to provide the DOS Settings that one should try for DOS communications programs in this section. The settings may not work on all systems. I will add to this section as I receive information from users. All DOS Settings that are not given should be at their defaults.

Seiko Smart Label Printer.
I tested the Seiko printer successfully using the following DOS settings for SIO: In addition, you should run the printer in its own separate Win-OS/2 session.
 * SIO_Mode_DTR               No Change at OPEN or CLOSE
 * SIO_Mode_FIFO_Load_Count   1.
 * SIO_Mode_IDSR              Ignore DSR During Receive
 * SIO_Mode_OCTS              Ignore CTS During Transmit
 * SIO_Mode_ODSR              Ignore DSR During Transmit
 * SIO_Mode_RTS               No Change at OPEN or CLOSE
 * SIO_Mode_XON/XOFF"         Received XON is flow control

IBM's SLIP
I have been told by many users that a MODE command is required for IBM's SLIP program to work correctly. The recommended MODE command is as follows: MODE DTR=ON

Differences between SIO/VSIO and COM/VCOM
What follows is some of the differences between SIO/VSIO and COM/VCOM that are known to the author.

1 - COM.SYS will automatically seek out and support four comm ports, COM1 through COM4. SIO.SYS will automatically seek out and support only COM1 and COM2. If SIO.SYS is to support more than two comm ports, they must be defined in the command line that loads SIO.SYS. For example, DEVICE=SIO.SYS (COM3) (COM4) will cause SIO.SYS to support four comm ports.

2 - In the absence of overrides in the command line, COM.SYS will seek out four comm ports in the sequence of I/O ports 3F8h, 2F8h, 3E8h and 2E8h. The first port found in this sequence is given the logical name COM1, the second is COM2 etc. This means that the comm port at 2F8h could become COM1. In the opinion of the author, this confuses some users to frustration.

With no command line overrides, SIO.SYS uses a fixed I/O port concept. That is, COM1 is always at I/O port 3F8h, COM2 is always at 2F8h, etc. Another way of looking at this is; if no comm port exists at port 3F8h, then you do not have a COM1. SIO.SYS will not move another (found) comm port into the logical COM1 slot.

3 - VSIO opens a comm port for a DOS session with sharing allowed. VCOM uses an "exclusive use" open for DOS sessions.

4 - SIO.SYS always controls the FIFOs of the 16550 UART. SIO.SYS will not allow an application program (OS2 or DOS) to disable the FIFOs of a real 16550. The application may specify the transmit fifo load count.

5 - SIO.SYS will accept any number between 50 and 115200 (921600 if a Hayes ESP) as a valid baud rate. For example, if an application program attempts to set a baud rate of 9990 bps, COM.SYS will reject it and SIO.SYS will accept it.

6 - SIO/VSIO execute faster than COM/VCOM. This means that some applications, that are timing dependent, may not work under SIO/VSIO that do work under COM/VCOM.

7 - SIO/VSIO provides more reliable active flow control for DOS sessions. For example, if RTS/CTS handshaking is in use, VSIO processes the RTS settings by the DOS program while SIO completely controls the real RTS signal. COM/VCOM simply passes the RTS signal directly to the hardware.

8 - COM.SYS will block an application until a write completes. SIO will return to the application program immediately if all of the write data will fit into SIO's internal buffers.

PROBLEMS AND SOLUTIONS
This message is displayed when the comm port or the IRQ is in use. If the comm port is not actually in use, the IRQ is most likely in use.
 * 1 - Port already in use is displayed.
 * 2 - SIO displays a warning message that the IRQ for a port appears to be wrong, but the port works.

SIO probably detected more than one IRQ attached to the comm port. This indicates a possible hardware problem with your system that you may want to have checked.

Configure your comm program(s) to insert a delay between modem initialization characters as they are sent to the modem.
 * 3 - The modem will not initialize.

During the WinFax install, temporarily turn OFF the DOS setting SIO_Virtualize_COM_Ports. Once installation is complete, the setting SIO_Virtualize_COM_Ports can be restored.
 * 4 - WinFax locks up during install.

Set the baud rate in Telemate to less than 57600.
 * 5 - Telemate does not recognize VX00 as a FOSSIL.

This is a problem common to many DOS BBS and Door programs. They attempt to synchronize the local screen with the transmitted data. That is, they send a character, wait until it is sent and then display the character on the local screen. This does not cause a problem for the single tasking DOS environment. However, this procedure causes at least two (probably more) context switches in the multi-tasking environment of OS2, which in turn brings the processor to its knees. One possible solution is for the programmer to synchronize line by line instead of character by character.
 * 6 - Comm output is very slow from DOS.

Procomm seems to have a bug in its implementation of RTS/CTS handshaking. The problem shows up most often when Procomm is windowed. Under certain conditions, Procomm will turn the virtual RTS OFF and does not turn it ON again. This prevents VSIO from sending further data to Procomm if SIO_Mode_RTS is set for RTS/CTS handshake. A solution to the problem that seems to work is to set SIO_Mode_RTS to other than RTS/CTS handshake. Note that SIO_Mode_RTS should be set for RTS/CTS handshake under almost all other conditions.
 * 7 - Procomm stops receiving

You should find the file PW2.INI in you main WINDOWS directory. Locate the statement DropRTSAroundDiskWrites=1 and change it to: DropRTSAroundDiskWrites=0
 * 8 - Procomm For Windows download errors


 * 9 - WinFax does not work well.
 * a - Connect problems with recipient's fax station
 * b - Cannot send more than one page of a multiple page fax
 * c - Transmission fails between pages
 * d - Transmitted pages are corrupted, missing parts, or cut off.

The modem init strings set by WinFax 3.0 will work in the single-layered comm world of DOS and Windows. However, these modem init strings will not work in the multi-layered comm environment used by OS/2. Specifically, WinFax 3.0 sets the modem to use only Xon/Xoff flow control. Ideally, both Xon/Xoff and Hardware handshaking needs to be set. If only one handshake can be set, set the modem to Hardware handshake. For USR FAX modems, use &H3, for many other modems, the setting is &K3. Additionally, for WinFax 3.04 and up, place the following in your WINFAX.INI file: HdwFlowControl=1
 * Class 1 FAX modem.

It seems to the author that hardware handshake screws up some (possibly all) class 2 FAX modems. Therefore, when using a class 2 modem, WinFax should be configured to use XON/XOFF handshaking. For WinFax 3.04 and up, place the following in your WINFAX.INI file: HdwFlowControl=0 The author feels that the inability to use hardware handshake with class 2 FAX modems is a serious design deficiency.
 * Class 2 FAX modem.

Add the following command line to your CONFIG.SYS file: RUN=MODE COM1 TO=ON
 * 10 - Serial Printer messes up on last page.

IRQ Sharing on ISA
Sharing the same IRQ for multiple communications ports on ISA systems is not for the weak of heart (or mind). If you have problems with shared IRQs, DO NOT contact the author. Contact the board or computer manufacturer for help.

Some general rules are as follows:
 * 1) Two different boards (plugged into different slots) can not share the same IRQ. This is a hardware limitation of ISA systems and can not be corrected by software. This means that you can not plug in two internal modems, set them for the same IRQ and expect them to work. This does not apply to PS/2 systems. The problem of multiple boards sharing the same IRQ was corrected in the PS/2's bus design.
 * 2) SIO can not (will not) share an IRQ with other device drivers at the same time. SIO releases IRQs that it is currently not using. This is different form how COM.SYS works. This difference may show up as an unexpected "port already in use" error that does not occur with COM.SYS. I have received reports that the SDLC drivers try to concurrently share IRQs with the ASYNC driver. SIO.SYS will not allow this while COM.SYS will.

Appendix A, Hardware Port and IRQ Assignments
I have obtained the following information from various sources. Accuracy is not guaranteed. In fact, nothing in this document is guaranteed.

Addresses and IRQs for COM1 and COM2 COM1 uses 03F8h and IRQ4 COM2 uses 02F8h and IRQ3 Defacto standard for COM3 and COM4 for PC, XT and AT COM3 uses 03E8h and IRQ4 COM4 uses 02E8h and IRQ3 Addresses and IRQ for COM3 through COM8 on the PS/2 COM3 uses 3220h and IRQ3 COM4 uses 3228h and IRQ3 COM5 uses 4220h and IRQ3 COM6 uses 4228h and IRQ3 COM7 uses 5220h and IRQ3 COM8 uses 5228h and IRQ3 All PCs (known to the author) prior to the PS/2 and EISA only use 10 bits to address hardware I/0 ports. Systems prior to the PS/2 and EISA can not address the standard PS/2 addresses for COM3 through COM8. If an AT or below attempts to address COM3 through COM8 using the PS/2 addresses, only the low 10 bits of the address are used. That is, the high digit of the hexadecimal address will be ignored. This means that any reference to COM3 through COM8 will actually address ports 220h through 22Fh on older PCs.

One should avoid expansion boards that use ports 220h through 22Fh unless the expansion board is a serial I/O board.

SIO will (attempt to) determine the hardware architecture (ISA/EISA and PS/2) that it is being executed on and use the appropriate hardware port addresses for COM1 thru COM4 as defaults.

Appendix B, SIO Chips
The following is a collection of comments developed from hearsay, random documents, experience, and technical specifications. So, take it with a grain of salt. Order information from the various manufactures if you want accurate information.

Very good reference books are available from National Semiconductor Corporation. They cover most of the SIO devices (also called UARTs) that you will find in many PCs and clones. I am not sure that books can be ordered directly from National semiconductor. They may require that you get it from a distributor. In any case, the address on the back of the one manual is:


 * National Semiconductor Corporation
 * 2900 Semiconductor Drive
 * P.O. Box 58090
 * Santa Clara, CA 95052-8090


 * Tel:(408)721-5000
 * TWX:(910)339-9240

8250
As best that I know, the 8250 was the first SIO chip (integrated circuit) that was used by the IBM PC and many clones. In my opinion, it was a poor choice on the part of IBM. I feel many superior devices, at comparable prices, were readily available. At that time, I feel the 8251A or the 8530 would have been better choices. But, they used the 8250 and therefore we must use it.

From a hardware standpoint the 8250 is a relatively slow device. It is advisable that programmers not perform successive inputs or outputs to this device. It seems that software programs can load the various registers of the 8250 faster than it can process the information. The 8250 had a total of 7 registers. The specifications state that 56kb is the maximum baud rate.

8250A
I believe the 8250A is the 8250 with some bug fixes. I have no idea what the bugs may have been. A quick glance at the specifications shows the speed of the 8250 and 8250A to be much the same. The 8250A added an 8th register. This additional register enables software to detect if an 8250 is installed. The specifications state that 56kb is the maximum baud rate.

16450
The 16450 seems to be a speeded up version of the 8250A. There is no direct way (that I know of) for software to detect the difference between an 8250A and a 16450. I believe the 16450 was developed to eliminate the need for software to insert delays between successive accesses to the device. The specifications indicate the 16450 is a much faster device than its predecessors. The additional speed is only the speed at which the processor can access the device. The maximum baud rate for the 16450 is still stated at 56kb. However, I have been told by some people that they have run the 16450 successfully at much higher speeds. I do not believe there was ever a 16450A.

16C451
The 16C451 is a CMOS version of the 16450. CMOS is a term for the material and manufacturing process used to make the part. CMOS typically uses less power than other technologies. If you are not designing hardware, you should view the 16C451 as a 16450.

16550 (Non A)
It is hard to find a 16550 (Non A). I was told by National Semiconductor that they did everything they could to get all 16550s back. SIO will detect a 16550 and tell you if you have one. I am told that the 16550 was installed in early PS/2 systems.

The 16550 was the first shot at a FIFOed version of the 8250 family from National semiconductor. However, I was told by National Semiconductor that the FIFOs of the 16550 are not reliable and they should not be enabled. SIO will treat a 16550 like a 16450. In this mode, they are reliable. National Semiconductor would not provide me with a specification for the 16550. However, I suspect its maximum baud rate is the same as the 16550A which is 256kb.

16550A, 16550AF and 16550AFN
In the manuals that I have, National Semiconductor does not explain the differences between the 16550A and the 16550AF. I suspect the AF part may have a few bug fixes. I believe the N in AFN describes packaging, ceramic versus plastic, DIP versus surface mount etc.

In the opinion of the author, there is no substitute for the 16550A (and its successors) in the 8250 type series. The 16550A is compatible with most software written for the entire family of 8250 type devices. Programs that are 16550A aware can provide much improved performance over previous devices.

The maximum baud rate for the 16550A is specified at 256kb. However, due to the hardware design of the PC et al, 115kb is the maximum baud rate that can be programmed by software.

The 16550A can be plugged into the same socket that contains an 8250, 8250A or 16450. If your SIO expansion board has the SIO chips in sockets, you can upgrade to the 16550A by simply removing the old chips and replacing them with 16550As.

The key to the performance increase of the 16550A is its FIFOs. It has 16 byte FIFOs for both transmit and receive data.

16550s Made by Western Digital
I have been told, but I have not verified for myself, that 16550s made by Western Digital have a problem with their FIFOs when working at 2400 baud or below.

16C551
The 16C551 is a CMOS version of the 16550AF. See the above description of the 16C451 for a discussion of CMOS. Do not feel you need to upgrade from a 16550A or AF to a 16C551. There is no gain from an existing users point of view.

16C552
The 16C552 is two 16C551s on a single chip.

16C554
The 16C554 is four 16C551s on a single chip.

82510
I believe Intel is the only company that manufactures the 82510. The 82510 is feature rich with several modes of operation. Its default mode is to operate as a 16450. The 82510 has a 4 byte FIFO for both transmit and receive data. A 4 byte FIFO is sufficient to provide significant performance over a basic 16450.

The 82510 is small in size. Therefore, it is found in many lap tops.

The 82510 is somewhat of a sleeper. I believe it would be much more widely used if Intel had promoted it more. However, given a choice between the 82510 and the 16550A, I would select the 16550A.

16650
The 16650 by Startech seems a good logical step in the evolution of the 8250 type UARTs. One of the many flavors of the 16650 is a package that is pin compatible with the 40 pin (DIP) 16550s. This means that the 16650 can be placed into the same socket as any 16550, 8250, etc.

The 16650 has enhanced the FIFOs to 32 bytes, added on chip flow control ability, and increases the maximum bit rate to 460800. The on chip flow control is a really nice feature. On chip flow control practically eliminates the possibility of missed receive characters. On chip flow control also means that some devices that require immediate attention when it sends Xoff, like the Seiko Label Printer, will work much better in environments like OS/2 and Windows.

The 32 byte FIFOs of the 16650 is an improvement over the 16550, but is still a disappointment. I feel that 1k, or larger, FIFOs would have been a much better choice. When I quizzed Startech about this, they replied that the 32 byte FIFOs were chosen to keep the cost down. They added that if the 16650 is successful, they plan a 16750 with larger FIFOs.

The 16650 powers up in a 16550 compatible mode, meaning most software written for the 16550 should work.

16750 from Texas Instruments
The 16750 from TI is an improvement over the 16550, but the omission of software flow control (Xon/Xoff) makes it inferior to the 16650, in the opinion of the author. The 16750 has a 64 byte fifo and hardware flow control. It is a good choice for a uart.

ComBic
The ComBic is a very impressive UART used on the Hayes ESP card and some others. The ComBic is basically a 16550 UART with on chip flow control and 1k FIFOs and a maximum bit rate of 921600. Like the 16650, on chip flow control practically eliminates the possibility of missed receive characters. On chip flow control also means that some devices that require immediate attention when it sends Xoff, like the Seiko Label Printer, will work much better in environments like OS/2 and Windows.

The ComBic has two modes of operation, compatibility mode and enhanced mode. In compatibility mode, the UART acts as a 16550. However, when in compatibility mode, the 1k FIFOs and on chip flow control can still be used. In enhanced mode, software gains the ability to look into the FIFOs and determine the exact number of bytes loaded. This feature enables software the use block input and output to the ComBic which greatly reduces processor overhead.

Appendix C, Multi-Port Serial I/0 Cards
I have received many requests for information about multi-port serial I/O card. I will describe the boards that I know about (or have heard about) here. I will add to the list as I receive precise information from manufactures, users, or I develop it myself.

Please do not contact me for support on the following boards, contact the manufacturer. The following tells of my experiences with the boards and does not imply support. Your experiences with a given board may be different.


 * NOTE:The Hayes ESP and Telcor Tport are described in the "Intelligent Cards Supported" section of this manual.

STB 4COM (ISA bus)
I am very impressed with the STB 4COM card, they have almost got it. Yes, its the same company that makes the VGA cards. The 4COM card uses a 16554 which is the equivalent of four 16550A. Comm ports can use IRQs 2/9, 3, 4, 5, 10, 11, 12, and 15. Any or all ports can share IRQs, and they have done this right. I tested SIO with all four ports of the 4COM on IRQ12 and they worked correctly. The user can select any of the following I/O port address for a comm port: 3F8, 2F8, 3E8, 2E8, 1A8, 1E8, 1F8, 2A8.

The 4COM card is priced at $110 and I ordered mine from Prerapture Solutions which can be reached by telephone at 1-919-286-1502 for information and foreign callers. In the US orders can be placed by calling 1-800-735-5266. Their mailing address is: Prerapture Solutions 1806 Albany St. Durham NC 27705-3135

Connect Tech Dflex-8
This is one of the most configure able communications cards that I have ever seen. It has on board simms to configure the electrical characteristics (RS232, RS442 etc). The board that I tested was configured for RS232 and has 8 Startech 16550 on it. All 8 ports can be jumpered to the same IRQ and the IRQ sharing seems to work well with SIO and I detected no performance problems.

I have no pricing information, the Dflex was supplied to me at no charge. Connect Tech can be reached at 519-836-1291. Their mailing address is: Connect Tech Inc. 727 Speedvale Ave. West Guelph, Ontario, Canada N1K 1E6

Gtek BBS550 (ISA bus)
The Gtek BBS550 is a communications card with the equivalent of 8 16550s (in reality two 16554s) UARTs. Where were these cards 5 years ago! Like the STB 4COM, I am very impressed with the BBS550. It has a wide range of selectable I/O port address, some in the 16 bit range (above 3FFh) which can be very useful. I tested the board with all 8 ports installed using IRQ3 (although I never had more than 3 ports active at the same time). The board performed well using shared IRQs.

The BBS550 has 8 RJ-45 connectors (10 pin), 6 of which comes directly off the back of the card. The other two RJ-45 connectors are internal and special cables with grommets are supplier for these 2 ports. The cables supplied with the BBS550 expands the RJ-45 out to standard DB-25 connectors.

Gtek is located in St. Louis Mississippi. Their phone number is 800-282-4835 or 601-467-8048.

Neotech Quad Serial (MCA bus)
Well, I just got my first PS/2 system (for testing of SIO) and I am using the NeoTech Quad Serial card in that system. What can I say, it works beautifully and interrupt sharing has never been a problem on MCA systems. This card (as shipped) came with four individual 16450 chips installed, but they were in sockets so I installed 16550 UARTs before I installed the card. The card has one large connector on the back of the card and the supplied cable expands that to 4 standard DB-25 connectors. Those of you needing a good 4 port card for an MCA system contact: Neotech Inc 30295 Solon Industrial Pkwy. Solon, Ohio 44139

Voice(216) 248-4114 FAX (216) 248-5701