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USERS MANUAL
SIO.SYS and VSIO.SYS, Serial Communications Device Driver
for OS/2 V2 (and up) and its Virtual DOS Machines (VDM).
Copyright (c) 1993 by Raymond L. Gwinn
12469 Cavalier Drive
Woodbridge, Virginia 22192
All Rights Reserved
June 15, 1993
Email
CompuServe 72570,157
Internet 72570.157@compuserve.com
FidoNet 1:265/104 (Routed Mail Only)
FAX
703-494-0595
i
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 Application
Programmers manual is being written.
This manual and the software distributed with it is provided with
no guarantees. Use it at your own risk.
Product Support
Extensive testing has been done to insure that this product works
on the widest possible range of OS/2 V2 (and up) systems. In
most cases, problems can be resolved by reading this manual
carefully.
Email and FAX are the only methods of support provided. Voice
support would overwhelm the author. If, after reading the manual
carefully, you are unable to resolve a problem, please fill out
PROBLEM.TXT (adding information as necessary) and Email/FAX it to
one of the following addresses:
Email
CompuServe 72570,157
Internet 72570.157@compuserve.com
FidoNet 1:265/104 (Routed Mail Only)
FAX
703-494-0595
PROBLEM.TXT is included in the distribution ZIP.
ii
TABLE OF CONTENTS
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . i
Product Support . . . . . . . . . . . . . . . . . . . . i
WHAT IS SIO . . . . . . . . . . . . . . . . . . . . . . . . . 1
WHAT IS VSIO . . . . . . . . . . . . . . . . . . . . . . . . 2
GETTING STARTED . . . . . . . . . . . . . . . . . . . . . . . 3
Installing SIO/VSIO . . . . . . . . . . . . . . . . . . . . . 3
Quick Start . . . . . . . . . . . . . . . . . . . . . . 3
COMMAND LINE OPTIONS . . . . . . . . . . . . . . . . . . . . 4
COM1 thru COMn . . . . . . . . . . . . . . . . . . . . . 4
I/O port address . . . . . . . . . . . . . . . . . . . . 4
IRQ number . . . . . . . . . . . . . . . . . . . . . . . 4
Forced 16550A . . . . . . . . . . . . . . . . . . . . . 4
AUTOMATIC IRQ ASSIGNMENT . . . . . . . . . . . . . . . . . . 5
DOS SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . 6
SIO_Allow_Access_COMn . . . . . . . . . . . . . . . . . 6
SIO_Virtualize_COM_Ports . . . . . . . . . . . . . . . . 6
SIO_Virtualize_16550A . . . . . . . . . . . . . . . . . 6
SIO_Virtual_RTS_is_HS . . . . . . . . . . . . . . . . . 6
Differences between SIO/VSIO and COM/VCOM . . . . . . . . . . 7
PROBLEMS AND SOLUTIONS . . . . . . . . . . . . . . . . . . . 8
IRQ for a port appears to be wrong . . . . . . . . . . . 8
The modem will not initialize . . . . . . . . . . . . . 8
WinFax locks up during install . . . . . . . . . . . . . 8
WinFax does not work well . . . . . . . . . . . . . . . 8
Telemate does not recognize VX00 as a FOSSIL . . . . . . 8
Output is very slow at 2400 baud and below . . . . . . . 8
FaxWorks' driver FMD.SYS . . . . . . . . . . . . . . . . 9
IRQ SHARING ON ISA . . . . . . . . . . . . . . . . . . . . 10
Appendix A, Hardware Port and IRQ Assignments . . . . . . . 11
Addresses and IRQs for COM1 and COM2 . . . . . . . . . 11
Defacto standard for COM3 and COM4 . . . . . . . . . . 11
Addresses and IRQ for COM3 through COM8 on the PS/2 . 11
Appendix B, SIO Chips . . . . . . . . . . . . . . . . . . . 12
8250 . . . . . . . . . . . . . . . . . . . . . . . . . 12
8250A . . . . . . . . . . . . . . . . . . . . . . . . 12
16450 . . . . . . . . . . . . . . . . . . . . . . . . 13
16C451 . . . . . . . . . . . . . . . . . . . . . . . . 13
iii
16550 (Non A . . . . . . . . . . . . . . . . . . . . . 13
16550A . . . . . . . . . . . . . . . . . . . . . . . . 13
16550AF . . . . . . . . . . . . . . . . . . . . . . . 13
16550AFN . . . . . . . . . . . . . . . . . . . . . . . 13
16550s Made by Western Digital . . . . . . . . . . . . 14
16C551 . . . . . . . . . . . . . . . . . . . . . . . . 14
16C552 . . . . . . . . . . . . . . . . . . . . . . . . 14
16C554 . . . . . . . . . . . . . . . . . . . . . . . . 14
82510 . . . . . . . . . . . . . . . . . . . . . . . . 14
Appendix C, Multi-Port Serial I/0 Cards . . . . . . . . . . 15
STB 4COM . . . . . . . . . . . . . . . . . . . . . . . 15
INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1
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. SIO.SYS does not support some
features that are provided by COM.SYS. In the view of the
author, these features are rarely used and they inhibit good
performance on the vast majority of systems. See the programmers
reference manual for information about the known differences
between COM.SYS and SIO.SYS.
SIO only works with 8250 (TYPE) serial I/O devices. Such devices
include 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. SIO will identify the type of serial devices that it
finds at load time.
Like other Device Drivers, SIO will do very little standing
alone. There must be an application(s) program to use SIO before
you will gain benefit.
2
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.
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. VSIO does not emulate any BIOS 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 regardless of the baud rate. Note that this
enabling of RTS/CTS handshaking is independent of the RTS/CTS
handshaking used by SIO.
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. VSIO will not work with any other
device driver like COM.SYS.
3
GETTING STARTED
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.
Quick Start
Copy SIO.SYS and VSIO.SYS to the root directory of your boot
drive or diskette.
If you are going to use standard communications ports, either
COM1 or COM2 on an ISA buss (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 know to the author.
If your setup is more complex, you must read on.
4
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.
"An" is a hexadecimal number that defines the base hardware
I/O port address for the communications port.
"In" is an IRQ number (0 thru 15) or the string IRQ0 thru
IRQ15. Is is best if one allows SIO to determine the IRQ,
see AUTOMATIC IRQ ASSIGNMENT below.
"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 four serial communications ports can
be defined and supported by SIO and VSIO.
5
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
6
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_.
The provided DOS Settings and their meaning follow:
"SIO_Allow_Access_COMn" (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).
"SIO_Virtualize_COM_Ports" 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).
"SIO_Virtualize_16550A" 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).
"SIO_Virtual_RTS_is_HS" This DOS setting defaults to ON and
it applies to all communications ports used by the DOS
session. When ON, VSIO treats RTS as a handshaking signal
from the DOS session. When OFF, VSIO passed the RTS setting
directly to the hardware. This setting MUST be on for all
high speed DOS communications. The only application, known
to the author, where this signal may (should) be turned off
is DOS programs that use true half duplex.
7
Differences between SIO/VSIO and COM/VCOM
What follows is some of the differences between SIO/VSIO and
COM/VCOM that are know 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 uses 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.
5 - SIO.SYS will accept any number between 50 and 115200 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 - The last decimal digit of a baud rate given to SIO must be
zero. SIO.SYS will not support baud rates like 75 or 134.5.
If given, they will be rounded to 80 and 130 respectively.
7 - SIO/VSIO execute faster than COM/VCOM. This means that some
applications, that are timing dependant, may not work under
SIO/VSIO that do work under COM/VCOM.
8 - VSIO optionally (and by default) simulates a 16550A for DOS
sessions. VCOM simulates a 8250/16450.
8
PROBLEMS AND SOLUTIONS
1 - Port already in use is displayed.
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.
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.
3 - The modem will not initialize.
Configure your comm program(s) to insert a delay between
modem initialization characters as they are sent to the
modem.
4 - WinFax locks up during install.
During the WinFax install, temporally turn OFF the DOS
setting SIO_Virtualize_COM_Ports. Once installation is
complete, the setting SIO_Virualize_COM_Ports can be
restored.
5 - WinFax does not work well.
The modem init strings set by WinFax (for some modems) 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,
in some cases, WinFax sets Xon/Xoff flow control (only) with
the modem. 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.
6 - Telemate does not recognize VX00 as a FOSSIL.
Set the baud rate in Telemate to less than 57600.
7 - Output is very slow at 2400 baud and below.
This is a bug in several BBS programs that originated in
QuickBBS. The problem has been corrected in QuickBBS by
Steve Gabrilowitz, QuickBBS's current author. Inform the
author of your comm program of the problem and to contact
Steve Gabrilowitz for additional information.
9
8 - FaxWorks' driver FMD.SYS cannot access a comm port when SIO
is used, but works okay with COM.SYS.
The problem may be that the comm port is in use (often by a
DOS program). In all cases known to the author, this has
been the case. That is, FMD.SYS can not access the port
because it is in use, and FMD.SYS does not report the
problem in a manner that is understandable to many users.
COM.SYS seems to have a bug that will allow an OS2 device
driver (like FMD.SYS) to use a comm port when it is in use
by a another device driver, and it (COM.SYS) does not cause
an error when it should. The exact conditions of this is
not fully understood by the author and the above supposition
may not be totally correct.
10
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 buss 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.
11
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 (know to the author) prior to the PS/2 only used 12 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 standard addresses, only the low 12 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.
You 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.
12
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.
13
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.
14
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.
15
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 users or develop it myself.
My personal experience and testing of SIO is with a board from
B&B computer. However, I had to modify the board to make it
share IRQs. Therefore I will not discuss this board.
STB 4COM (ISA buss)
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.
I purchased my 4COM card (for $119) from Steve Winter, 800-735-
5266 or 919-286-1502.
16
INDEX
16450 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
16550 Non A . . . . . . . . . . . . . . . . . . . . . . . . . 13
16550A . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
16550AF . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
16550AFN . . . . . . . . . . . . . . . . . . . . . . . . . . 13
16550s Made by Western Digital . . . . . . . . . . . . . . . 14
16C451 . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
16C551 . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
16C552 . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
16C554 . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8250 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8250A . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
82510 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Addresses and IRQ for COM3 through COM8 on the PS/2 . . . . . 11
Addresses and IRQs for COM1 and COM2 . . . . . . . . . . . . 11
Allow_Access_COMn . . . . . . . . . . . . . . . . . . . . . . . 6
Appendix A, Hardware Notes . . . . . . . . . . . . . . . . . 11
Appendix B, SIO Chips . . . . . . . . . . . . . . . . . . . . 12
Appendix C, Multi-Port Serial I/0 Cards . . . . . . . . . . . 15
AUTOMATIC IRQ ASSIGNMENT . . . . . . . . . . . . . . . . . . . 5
COMn already in use . . . . . . . . . . . . . . . . . . . . . . 8
CONFIG.SYS . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Defacto standard for COM3 and COM4 . . . . . . . . . . . . . 11
Differences between SIO/VSIO and COM/VCOM . . . . . . . . . . . 7
DOS SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . . 6
FaxWorks . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
FIFO . . . . . . . . . . . . . . . . . . . . . . . . . . 13, 14
FMD.SYS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
GETTING STARTED . . . . . . . . . . . . . . . . . . . . . . . . 3
Installing SIO/VSIO . . . . . . . . . . . . . . . . . . . . . . 3
IRQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4, 5
IRQ SHARING ON ISA . . . . . . . . . . . . . . . . . . . . . 10
National Semiconductor Corporation . . . . . . . . . . . . . 12
PDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Physical Device Driver . . . . . . . . . . . . . . . . . . . . 2
PKUNZIP . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Authentic files . . . . . . . . . . . . . . . . . . . . . 3
PROBLEMS AND SOLUTIONS . . . . . . . . . . . . . . . . . . . . 8
Quick Start . . . . . . . . . . . . . . . . . . . . . . . . . . 3
RTS/CTS handshaking . . . . . . . . . . . . . . . . . . . . . . 2
SIO Chips . . . . . . . . . . . . . . . . . . . . . . . . . . 12
SIO_Virtual_RTS_is_HS . . . . . . . . . . . . . . . . . . . . . 6
STB 4COM . . . . . . . . . . . . . . . . . . . . . . . . . . 15
UART . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
VDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Virtual Device Driver . . . . . . . . . . . . . . . . . . . . . 2
Virtualize_16550A_For_COM . . . . . . . . . . . . . . . . . . . 6
Virtualize_COM_Ports . . . . . . . . . . . . . . . . . . . . . 6
WHAT IS SIO . . . . . . . . . . . . . . . . . . . . . . . . . . 1
WHAT IS VSIO . . . . . . . . . . . . . . . . . . . . . . . . . 2
17
WinFax . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
