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VMODEM
Technical Reference Manual



Copyright (c) 1995 by Raymond L. Gwinn
12469 Cavalier Drive
Woodbridge, Virginia 22192
All Rights Reserved

January 13, 1995


CompuServe: 71154,575
InterNet: [email protected]
Voice: 1-703-494-4673
FAX: 1-703-494-0595
BBS: 1-703-494-0098 or 199.248.240.2
















INTRODUCTION

The Virtual Modem is a concept that the author believes will
change the way serial data communications is done and thought of.
It is going to bring the Internet alive more then ever before.
Perhaps it will not be this implementation of a Virtual Modem,
but the concept will remain and be used for a long time. The
concept of the Virtual Modem was born from the desire to make the
SIO support BBS available via Internet. In only a few minutes, I
was convinced the Virtual Modem was a solution of a multitude of
problems that Internet access poses.

The Virtual Modem removes most of the complexities and mysteries
of the Internet by allowing common, well understood, programs to
be used to access the Internet highway. Users can use programs
like PmComm and TE/2 to download files from a BBS (across the
Internet) using common protocols like ZMODEM. The dialing
directories of terminal programs can contain Internet addresses
instead of phone numbers for easy access to remote sites.

BBS SysOps can simply declare one or more of their BBS's
communications ports as a Virtual Modem and users can then "dial"
in over the Internet and no BBS software changes should be
necessary. Is your BBS ready for 20 million new users that can
access it without making a long distance call? This Virtual
Modem implements protocols, including a Telnet server which
allows most anyone on Internet to access your system.

Users transferring large volumes of data across phone lines (like
FidoNet echomail) can now use the Internet highway instead.
Again, software changes should be minimal, if any at all.

Vmodem is unique in that it has a dual personality of both Server
and Client. The Server/Client personality is determined by the
direction of the connection (outgoing or incoming).







ii

TABLE OF CONTENTS

WHAT IS VMODEM . . . . . . . . . . . . . . . . . . . . . . . 1

DISTRIBUTION, ORDERING AND SUPPORT . . . . . . . . . . . . . 2
Distribution and Ordering . . . . . . . . . . . . . . . 2
SIO Distribution and Support BBS . . . . . . . . . 2
Support . . . . . . . . . . . . . . . . . . . . . . . . 2

GETTING IT GOING . . . . . . . . . . . . . . . . . . . . . . 5
TCP/IP Required . . . . . . . . . . . . . . . . . . . . 5
TCP/IP Sockets . . . . . . . . . . . . . . . . . . 5
The default port number . . . . . . . . . . . . . . 5

The SIO.SYS command line . . . . . . . . . . . . . . . . . . 5

THE VIRTUAL MODEM . . . . . . . . . . . . . . . . . . . . . . 7
AT Commands Supported . . . . . . . . . . . . . . . . . 7
S Registers Supported . . . . . . . . . . . . . . . . . 8
Result Codes . . . . . . . . . . . . . . . . . . . . . . 8
NO CARRIER . . . . . . . . . . . . . . . . . . . . 8
NO DIALTONE . . . . . . . . . . . . . . . . . . . . 8
. . . . . . . . . . . . . . . . . . . . . . . . . 8
BUSY . . . . . . . . . . . . . . . . . . . . . . . 8
CONNECT 57600/ARQ/VMP . . . . . . . . . . . . . . . 8
CONNECT 57600/ARQ/TEL . . . . . . . . . . . . . . . 8
RING . . . . . . . . . . . . . . . . . . . . . . . 8
RINGING . . . . . . . . . . . . . . . . . . . . . . 9
Caveats . . . . . . . . . . . . . . . . . . . . . . . . 9

SECURITY . . . . . . . . . . . . . . . . . . . . . . . . . 10
Discussion . . . . . . . . . . . . . . . . . . . . . . 10
Vmodem's Implementation . . . . . . . . . . . . . . . 10
Developers Information . . . . . . . . . . . . . . . . 11

DIALING EXAMPLES . . . . . . . . . . . . . . . . . . . . . 12

Telnet . . . . . . . . . . . . . . . . . . . . . . . . . . 13
IBM's Telnet Client . . . . . . . . . . . . . . . . . 13

Development and Debugging Tools . . . . . . . . . . . . . . 14
The Poor Man's Line Monitor (PMLM.EXE) . . . . . . . . 14
VIEWPMLM.EXE . . . . . . . . . . . . . . . . . . . . . 15
SIO's Utility (SU.EXE) . . . . . . . . . . . . . . . . 15
IRQs that currently free for use . . . . . . . . 15

Appendix A, Hardware Port and IRQ Assignments . . . . . . . 16
Addresses and IRQs for COM1 and COM2 . . . . . . . . . 16
Defacto standard for COM3 and COM4 . . . . . . . . . . 16
Addresses and IRQ for COM3 through COM8 on the PS/2 . 16

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . 17







iii







1









WHAT IS VMODEM

Vmodem is a software implementation of a modem, referred to as a
Virtual Modem. Basically, it attempts to fake out other software
(like terminal programs) into believing they are accessing a real
modem. Vmodem will turn any Terminal into a Telnet Client, and
any BBS into a Telnet Server.

Normal (real) modems provide an interface that allows terminal
programs to pass digital information across telephone lines.
Vmodem does the same thing from the application (terminal)
program's point of view. However, the other side of Vmodem is
not a phone line, but a digital network like Internet. Thus,
Vmodem allows the hoards of communications programs to pass
information across Internet instead of using phone lines.

In addition to acting as a Telnet server, Vmodem uses a newly
designed protocol for communications networks, called the Virtual
Modem Protocol (VMP). At this time, no other programs have
implemented VMP, thus Vmodem is required on both ends of the
connection to use the VMP. However, VMODEM.EXE will accept
inbound Telnet connections from any system, meaning a BBS under
vmodem can be accessed by just about anyone with an Internet
connection.

Future implementations of Vmodem may access networks other than
Internet and use TCP/IP implementations other than IBM's. The
current implementation of Vmodem works only on Internet, using
the Internet Access Kit (IAK) that is included with OS/2 V3 and
IBM's TCP/IP (for OS/2) version 2.0, with the August 1994 CSD
applied.

A single invocation of Vmodem can service all of the Internet
ports defined in the SIO command line.







2

DISTRIBUTION, ORDERING AND SUPPORT

Distribution and Ordering

Vmodem is a part of a larger package collectively known as SIO.
The entire package collectively known as SIO is ShareWare. It is
not free software or freeware. See LICENSE.TXT and ORDER.TXT for
additional information. The ShareWare version of SIO is
distributed electronically. One may check their favorite
electronic hangout for the latest version of SIO. The latest
copy of the ShareWare version is always posted for downloading
from the BBS at 1-703-494-0098 or 199.248.240.2. ShareWare
versions of SIO can also be downloaded from the CompuServe Forum
OS2BVEN, library 4.

Registered versions of SIO are distributed by US Mail and
electronically from the SIO Distribution and Support BBS. Users
desiring to register electronically, may call the BBS and
register on line (1-703-494-0098 or 199.248.240.2) and
immediately download their registered version of SIO. Use the
ORDER command at the main BBS prompt.

Registrations/Orders can also be placed by phone, mail, FAX, and
email. See the front cover of this manual for the phone numbers
and addresses. Also see ORDER.TXT for and order form that may be
used.

Support

Only product support is provided, user support for Vmodem is NOT
provided. That is, help with application program configuration,
modem init strings etc, is not provided. Product information
such as bug reports, suggestions, and information about
incompatibilities are welcome. They should be sent to one of the
following addresses.


Email
CompuServe 71154,575
Internet [email protected]
FAX 1-703-494-0595
BBS 1-703-494-0098 or 199.248.240.2







3

QUICK START


If some of your applications do not work, it is probably due to
the timing difference between the virtual modem and real modems.
These type of problems are NOT bugs in Vmodem, but in the
application itself and should be reported to the support
department for the application program. Thus, messages saying
that application XYZ does not work are probably of no value and
may be ignored.

The Good Stuff Starts Here:

If you do not have TCP/IP up and running on your system, forget
it, there is no quick start. If TCP/IP is running on your system
then read on.

Users of the IBM Internet Access Kit (IAK) and IBM's SLIP be sure
to execute MODE COMn DTR=ON somewhere before you attempt to dial
in.

First, you must define one or more Virtual Modem ports in the
SIO.SYS command line and reboot. DO NOT DEFINE A PORT THAT IS
CONNECTED TO A REAL MODEM AS AN INTERNET PORT. Defining a
Virtual Modem port simply requires that you use the word
"Internet" instead of the I/O port address in the SIO command
line. Do not forget to assign the DOS reflection stuff if you
will use the port from DOS sessions. An SIO command line example
using COM4 as a Virtual Modem is:

DEVICE=SIO (COM1,3F8,4) (COM4,INTERNET:2E8,NONE:3)

The ":2E8" and the ":3" in the command line tells SIO to reflect
data to DOS sessions on virtual I/O port 2E8 and virtual IRQ3.
The "NONE" in the command line indicates that no real IRQ is
used.

After you have made the SIO command line changes, and rebooted,
you must first activate TCP/IP. Users of the IBM Internet Access
Kit must initiate a connection in the normal manner before Vmodem
will start. After TCP/IP is activated, type Vmodem at any OS/2
prompt. The Vmodem display attempts to simulate a modem display.
An activity log will start at the bottom of the display and
scroll up to the bottom of the simulated LED display. If you
wish, you can use "START /min Vmodem" to invoke Vmodem in your
TCP/IP start up scripts, TCPEXIT.CMD is the best place. Hit
Control C if you wish to terminate Vmodem, but you must leave it
running if you want Virtual Modem support.







4


Once Vmodem is started, any access to COM4 (in this example) will
go out over the Internet. Bring up your favorite terminal
program, configured for COM4, and type "AT?" for a list of
supported AT commands. To dial out, type ATDT inetaddr.com, of
course you must use a real Internet address.

As of this writing, there are several BBSes available for
incoming calls using Vmodem. Their Internet addresses are:

199.248.240.2 SIO Support in Virginia
199.100.191.2 Bob Juge in Houston Texas
199.67.41.2 PCBOARD, Clark Development
198.69.157.10 Steve Haynes, in Virginia
198.68.171.210 File Bank BBS
198.68.17.57 Paul Breedlove, Multinet
199.3.36.205 Steve Schmidt in Chicago Illinois
198.96.20.209 Steven Bonisteel in Canada
194.70.36.10 Jon Morby in England
198.17.249.111 Pete Link in USA
199.165.149.4 Pete Person in Washington State
bbs.adam.anet.cz Tomas Kucera in Prague, CZ







5

GETTING IT GOING


TCP/IP Required

The current (first) implementation of Vmodem and works only with
the Internet Access Kit (IAK) that is included with OS/2 V3 and
IBM's TCP/IP V2.0 with the August 1994 CSD applied. Contact IBM
for information about obtaining their TCP/IP and the CSD update.

Prior to executing Vmodem, you should have TCP/IP installed and
operational on your system. The author is far from an Internet
or TCP/IP expert (more like a novice) so you are on your own in
getting TCP/IP up on your system.

Users of the IBM Internet Access Kit (IAK) and IBM's SLIP be sure
to execute MODE COMn DTR=ON somewhere before you attempt to dial
in.

The Virtual Modem Protocol (VMP) that is implemented by Vmodem
uses TCP/IP Sockets. The default port number used by Vmodem is
3141 (the first 4 digits of pi, un-rounded). However, this
default port number can be overridden by using the SERVICES file
in the TCP/IP ETC directory. If the user defines a "Well Known
Port" called "vmodem" (lower case) in the SERVICES file, then
that port will be used instead of 3141. The port number 3141 has
been assigned to the Virtual Modem Protocol (VMP) by the Internet
Assigned Numbers Authority (IANA). The name associated with port
3141 is "vmodem" (without the quotes). Likewise, the Telent
Server in Vmodem can be directed to use any port number by adding
a "Well Known Port" called VMOTelnet to your SERVICES file. The
Telnet Server defaults to port 23 (the standard Telnet port).

The SIO.SYS command line

If you do not already know what SIO.SYS is, you should start with
the SIO Users Manual which should be a part of the same package
that contained this manual. The Vmodem specific part of the SIO
command line is only documented here.

The changes to the SIO command line to define a Virtual Modem
Port(s) is simple. All one does is to replace the I/O port
number with the word "Internet" (without the quote marks). I/O
port number are usually hexadecimal numbers like 3F8 (for COM1)
and it is this number that is replaced with the word "Internet".
A command line example for a Virtual Modem on COM4 that will only
be accessed by native OS/2 programs is as follows:

DEVICE=SIO.SYS (COM1) (COM4,INTERNET,NONE)

The "NONE" in the above simply states that no IRQ is being used.







6


If one wishes to access the Virtual Modem from DOS and/or Windows
sessions, the command line is a little more complicated. You
must tell SIO where to present the information to the DOS/Windows
session. That is, you must tell SIO (really VSIO) the virtual
I/O port number and the virtual IRQ that the DOS/Windows
application uses to access the port. Continuing to use COM4 as
the example should be changed to:

DEVICE=SIO.SYS (COM1) (COM4,INTERNET:2E8,NONE:3)

This command line will present a standard COM4 to the DOS and or
Windows session(s).







7

THE VIRTUAL MODEM

Starting the Virtual Modem is about as simple as it can be.
Simply type VMODEM or START /MIN VMODEM at any OS/2 prompt, there
are no required command line parameters. Vmodem then just sits
there and displays some minimal activity reports. Vmodem does
have one optional command line parameter, a log file name. If a
log file name is given, all information displayed on the Vmodem
screen is written to the file.

Once started, and with the above mentioned additions to the SIO
command line, application programs should see a relatively simple
modem that implements a very basic set of AT commands. Most of
the AT commands of a real modem simply do not apply in the
environment that the Virtual Modem is being used in. For
example, flow control is automatic (done by TCP/IP) so the
virtual modem needs no flow control commands.

Remember, the Virtual Modem has no memory, so any needed modem
init string needs to be presented each time an application
program is executed.

AT Commands Supported

? Display a list of supported AT commands.

DT Dial the following internet address.

En Command mode local echo. E0 disables echoing, E1
enables echoing.

Fn Local echo after connection. F0 enables (half duplex),
and F1 disables. This command is currently disabled.

Hn On/Off hook control. H0 or H alone to hang up, H1 go
off hook.

Mn Incoming connect notify. M0 or M alone inhibits
speaker sounds, and M1 enables speaker sound when an
incoming connect is detected.

Sr=n Set S register r to n. The supported set of S
registers is given below.

Sr=? Display the current value (setting) of S register r.

S? Display supported S register information.

Z Virtual modem reset.

&Cn Carrier detect operation, &C0 always on, &C1 normal.







8

&Sn DSR operation, &S0 always on, &S1 normal.

&V View virtual modem settings.


S Registers Supported

S0 Zero disables automatic answer, non-zero enables
automatic answer.

S7 Number of seconds to wait for carrier (connection) when
dialing.

S19 Set inactivity timer (automatic disconnect) in minutes
(0 disables). This S register is currently ignored by
Vmodem.

S38 Duration in seconds before disconnect when DTR drops.
This S register is currently ignored by Vmodem.


Result Codes

NO CARRIER. This result is returned when a dialing timeout
occurs or when an established connection terminates. The
timeout interval is specified by S register 7.

NO DIALTONE. This result code means that Vmodem could not
obtain address information from the name server (or HOSTS
file), or that the given Internet address is invalid. This
result code is also returned if TCP/IP is not responding.

BUSY. This result means that a connection to the vmodem
port was established at the remote site. However, no
available communications ports (COM1, COM2 etc) were
available to assign the connection to.

CONNECT 57600/ARQ/VMP. This result means the dialing and
session establishment occurred without problems and is ready
for user data flow using the Virtual Modem Protocol. The
given bit rate of 57600 is given only to satisfy the
application program. The actual data rate is not know to
Vmodem.

CONNECT 57600/ARQ/TEL. This result is the same as above
except the protocol being used is Telnet.

RING. This result means that an incoming connection has
been made with a remote system and that the local Vmodem is
sending a ring indication to the assigned communications
port (COM1 etc).







9

RINGING. This result means that an outgoing connection has
been made with a remote system and that the remote Vmodem is
sending a ring indication to the communications port.


Caveats

The modem command mode escape sequence, usually +++, is not
implemented by the Virtual Modem. Once the Virtual Modem enters
data mode, the only way to return to command mode is to drop DTR.
This is why the DTR override AT command is not supported.
Implementation of the escape (+++) feature would have a severe
impact on processor overhead and Virtual Modem throughput.

Numeric result codes are not currently implemented, they may be
at a future time.

Some application programs (like ProComm) translate letters into
numbers. I have not found a way to use ProComm's dialing
directory to pass alphabetic strings like those used in Internet
addresses.

Other applications (like TE/2) will pass alphabetic strings when
they are enclosed in double quotes. Thus, an Internet address
can be entered into TE/2's dialing directories in the form
"vmbbs.xyz.com". The trailing quote is not really necessary as a
trailing carriage return will also terminate the address.







10

SECURITY

Discussion
Some believe that logging onto a BBS via Internet is not as
secure as logging onto the same BBS using phone lines.
There are rumors of "sniffer" programs on the Internet
looking for credit card numbers, passwords and the like.
The phone line analogy of a sniffer is a tapped phone line.
The author has heard the rumors, but has never heard of a
confirmed case of a sniffer that really worked.

Vmodem attempts to remove the problem of passwords being
sent in the clear by implementing a "Shared Secret" password
encryption method, an Internet standard (see RFC 1321 and
RFC 1725). Depending on the BBS implementation, the "Shared
Secret" may (or may not) be your password. Contact your BBS
Sysop, or BBS supplier if you have questions about the
details.

The way the Shared Secret works is that the BBS sends a
unique string each time a connection is made. The contents
of the unique string is not important so long as it is
unique (different) each time a logon occurs. Your Shared
Secret (probably your password) is then appended to the
unique string and processed by something called the MD5
algorithm that produces yet a third string which is sent
back to the BBS. The BBS also processes the unique string
and the Shared Secret by the MD5 algorithm and compares the
result to the one received from the user. If they match,
then the BBS can proceed without directly asking the user
for their password. The unique string and the MD5
processing insure that a logon sequence is NEVER the same
and the Shared Secret is never directly send across the
network. The SIO support BBS supports the Shared Secret
login.

Vmodem's Implementation

Vmodem allows the user to specify the Shared Secret as a
quoted string in the dialing command. For example, if
Vmodem processes the following:

ATDT 199.248.240.2 "Hi There"

The Shared Secret is "Hi There" (the Shared Secret does not
include the quote marks). If Vmodem process the above ATDT
command and sees the unique string from the BBS, then a
proper response is returned to the BBS. The reader should
note that the Shared Secret is case sensitive. That is "hi
there" is NOT the same as "Hi There".







11

Developers Information

A document for developers describing the Share Secret
procedure and source code for the MD5 algorithm is
available from the author. Send requests for MD5.ZIP
via email to [email protected].







12

DIALING EXAMPLES

Vmodem will translate any "*" (asterisk) in the dialing string to
a "." (dot). Some terminal programs refuse to pass the dot, but
should pass the asterisk because it is a key on telephone
keypads.

The following are a few dialing examples to numeric type internet
addresses.


ATDT199.100.191.2 Bob Juge in Houston Texas
ATDT 199.67.41.2 PCBOARD, Clark Development
ATDT 199*3*36*205 Steve Schmidt in Chicago Illinois
atdt198.96.20.209 Steven Bonisteel in Canada
ATDT194*70*36*10 Jon Morby in England


Vmodem implements two different Internet protocols, Telnet and
VMP. VMP is Vmodem to Vmodem only, but is true binary while
Telnet it not. The Internet protocol that Vmodem uses when
making an outgoing connect is specified in the ATDT command by
preceding the Internet address with a pound sign "#". If the
pound sign precedes the Internet address, then VMP is used.
Otherwise, Telnet is used. Again, the reader should note that
VMP should be used only when you know your are connecting to
another Vmodem on the remote.

The following are a few dialing examples to non-existent internet
addresses using host names. At least I believe they do not
exist.

ATDT vmbbs.gwinn.com (use Telnet protocol)

ATDT #vmbbs.gwinn.com (use VMP protocol)

ATDTvmbbs.internet.com

ATDP "BBS.INTERNET.COM"

ATDT VMBBS.INTERNET.COM

ATDT vmbbs.internet.com 1234

In the above example, the user is specifying a port override.
Normally Vmodem will attempt a connect on port 3141 (the official
port for vmodem). In this case, the dialer is telling Vmodem to
use port 1234 instead of 3141.







13

Telnet

Vmodem implements a Telent server meaning that inbound Telent
connections are accepted. The "well know name" for the Telnet
server is VMOTelnet. The default port is the standard Telnet
port, 23. The port used by the Telnet server can be changed by
adding a line to the SERVICES file in your ETC directory and
assigning VMOTelent to another port. This can also be done to
disable the Telnet server part of Vmodem.

The best Telnet Client to use to connect to a Vmodem Telnet
Server is a terminal program also executing under Vmodem. Vmodem
can concurrently act as a Client and Server, meaning Vmodem can
connect to itself on the same system. This feature is a very
good testing tool. Of course, you can connect from a remote
system as well.

IBM's Telnet Client

IBM's Telnet seems to be a little finicky, but I did get it to
connect and work with a Vmodem host. I executed IBM's Telnet
with the following command line:

telnet -t ANSI -c NONE

In addition, after Telent loads I had to enter the following:

toggle crlf

BE SURE TO ENTER THE ABOVE COMMAND AFTER EXECUTING IBM'S TELENT.
Things are really screwy if you do not.







14

Development and Debugging Tools

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 signals transition to OFF is displayed in lower case
and a signals 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.TEC 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.







15


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 currently free for use.
Commands are provided allowing user control (missing from MODE)
are available. Status commands provide a wealth of diagnostic
information.







16

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 6 bits of the address will
be ignored by the hardware. 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.







17

Index

Addresses and IRQ for COM3 through COM8 on the PS/2 . . . . . 16
Addresses and IRQs for COM1 and COM2 . . . . . . . . . . . . 16
Appendix A, Hardware Notes . . . . . . . . . . . . . . . . . 16
AT Commands Supported . . . . . . . . . . . . . . . . . . . . . 7
BBS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Caveats . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Defacto standard for COM3 and COM4 . . . . . . . . . . . . . 16
Default port number . . . . . . . . . . . . . . . . . . . . . . 5
Development and Debugging Tools . . . . . . . . . . . . . . . 14
DIALING EXAMPLES . . . . . . . . . . . . . . . . . . . . . . 12
Distribution . . . . . . . . . . . . . . . . . . . . . . . . . 2
GETTING IT GOING . . . . . . . . . . . . . . . . . . . . . . . 5
IBM's Telnet Client . . . . . . . . . . . . . . . . . . . . . 13
Ordering . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
PMLM.EXE . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Result Codes . . . . . . . . . . . . . . . . . . . . . . . . . 8
S Registers Supported . . . . . . . . . . . . . . . . . . . . . 8
SECURITY . . . . . . . . . . . . . . . . . . . . . . . . . . 10
SIO's Utility (SU.EXE) . . . . . . . . . . . . . . . . . . . 15
Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
TCP/IP Required . . . . . . . . . . . . . . . . . . . . . . . . 5
TCP/IP Sockets . . . . . . . . . . . . . . . . . . . . . . . . 5
Telnet . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
The SIO.SYS command line . . . . . . . . . . . . . . . . . . . 5
THE VIRTUAL MODEM . . . . . . . . . . . . . . . . . . . . . . . 7
VIEWPMLM.EXE . . . . . . . . . . . . . . . . . . . . . . . . 15
WHAT IS VMODEM . . . . . . . . . . . . . . . . . . . . . . . . 1