VMODEM
Technical Reference Manual
Copyright (c) 1995 by Raymond L. Gwinn
26 Tanager Place
Beckley, West Virginia 25801
All Rights Reserved
August 10, 1995
CompuServe: 71154,575
InterNet: ray@gwinn.com
Voice: 1-304-255-7900
FAX: 1-304-255-7902
BBS: 1-304-255-7903 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 . . . . . . . . . . . . . . . . . . . . . . . . 8
Caveats . . . . . . . . . . . . . . . . . . . . . . . . . . 10
SECURITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 11
Vmodem's Implementation . . . . . . . . . . . . . . . . . . 11
Developers Information . . . . . . . . . . . . . . . . . . . 11
DIALING EXAMPLES . . . . . . . . . . . . . . . . . . . . . . . . 12
Telnet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
IBM's Telnet Client . . . . . . . . . . . . . . . . . . . . 13
Development and Debugging Tools . . . . . . . . . . . . . . . . . 14
Vmodem's Semaphores . . . . . . . . . . . . . . . . . . . . 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
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 1-304-255-7903 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 (1-304-255-7903 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 ray@gwinn.com
FAX 1-304-255-7902
BBS 1-304-255-7903 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
bbs.tfb.com File Bank BBS
bbs.multinet.com Paul Breedlove, Multinet
199.3.36.205 Steve Schmidt in Chicago Illinois
198.96.20.209 Steven Bonisteel in Canada
bbs.fidouk.org 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
202.12.87.130 Russell Coker, in Australia
volvo.datacomm.com Tony Wagner, West Coast USA
198.70.175.40 Bob Palmer, Belton MO
199.190.72.11 Patty and Roger Morris, LA
203.4.149.97 Dave Blears, Australia
204.91.224.2 Bridgewater, New Jersey
199.227.57.1 Steve Tower, Florida (I think)
tgax.com Sysop Adam Shiffman
bbs.os2bbs.com Pete Norloff, OS/2 Shareware BBS
vegas.roc.servtech.com Mike Utell
204.177.236.30 Stephen Albinda
os2nw.inetnw.com Dennis Peterson
blast.neta.com Blastronics
#os2nw.inetnw.com OS/2 Northwest BBS, Bellevue, WA
131.252.72.105 The PSU Econometrics Lab BBS
199.1.42.100 Gary Butters, Irving Texas
bbs.abaforum.es David Llamas, Barcelona Spain
142.222.15.220 Mohawk College, Hamilton Ontario Canada
gateway.execnet.com Ken Prevo
204.157.224.247 Leroy Devries
155.212.31.34 Richard Ploski
snoval.aa.net Larry Devers, Seattle WA
199.1.42.117 Chuck Hogard, Grand Prairie, Tx
october.com Bob Quinlan, Sunnyvale, CA
198.110.68.22 Walter Martin Braunohler
204.191.50.2 Jim Wright
199.3.29.10 Gene Angel
bbs.gco.com Bill Cook, Greater Chicago Online
onestop.donet.com Anthony Cogan
hightech.iadfw.net Brent Alberts, Dallas Texas
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 Telnet 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.
&Sn DSR operation, &S0 always on, &S1 normal.
8
&T Allows specification of a quoted string that Vmodem will
report to a remote as the terminal type for Telnet sessions.
ie AT&T"ANSI". This setting is reset to "ANSI" when ATZ is
executed.
&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).
RINGING. This result means that an outgoing connection has been
made with a remote system and that the remote Vmodem is sending a
9
ring indication to the communications port.
10
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.
11
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".
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
ray@gwinn.com.
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 Telnet server meaning that inbound Telnet
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 VMOTelnet 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 Telnet loads I had to enter the following:
toggle crlf
BE SURE TO ENTER THE ABOVE COMMAND AFTER EXECUTING IBM'S TELNET.
Things are really screwy if you do not.
14
Development and Debugging Tools
Vmodem's Semaphores
Vmodem creates two system semaphores for each supported port. One of
the semaphores is useable by 16 bit code, the other is usable by 32
bit code. Both the 16 and 32 bit semaphores are set and cleared at
the same time. The names are \SEM\VMODEMn and \SEM32\VMODEMn, where n
is the port number (1 or more decimal digits). The semaphores are set
at load time and when a disconnect occurs. The semaphores are cleared
when Vmodem starts "ringing" a communications port indicating an
incoming connect attempt. Programs can test the semaphore(s) and
spawn a program to process an incoming call (connect).
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.
15
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.
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Semaphores . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
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