Category : Network Files
Archive   : TANDEM2X.ZIP
Filename : TANDEM.DOC

Output of file : TANDEM.DOC contained in archive : TANDEM2X.ZIP


Rev. 2.0

Copyright (C) 1988 - Louis E. Wheeler
All Rights Reserved


The TANDEM Remote System is warranted to be free from copying defects
when shipped. There are no other warranties, expressed or implied,
including, but not limited to, any implied warranties of merchantability
or fitness for any particular application. In no event will Louis E.
Wheeler be liable for consequential damages even if advised of the
possibility of such damages. This software has been thoroughly tested,
but there may be bugs for which Louis E. Wheeler cannot be held
responsible. No liability or responsibility is assumed to the customer
or any other person or organization for any application or use of this
software or documentation sold or distributed by Louis E. Wheeler or any

Table of Contents

The TANDEM Remote System . . . . . . . . . 1

Equipment Requirements . . . . . . . . . . 2

Getting Started . . . . . . . . . . . . . 4

Passwords . . . . . . . . . . . . . . . . 7

Operating TANDEM . . . . . . . . . . . . . 8

Problem Programs . . . . . . . . . . . . . 11

In Case of Difficulty . . . . . . . . . . 12

User Support . . . . . . . . . . . . . . 13

The TANDEM Remote System

Rev. 2.0

Tandem adj. 1: consisting of things or having
parts arranged one behind the other 2: work-
ing in conjunction with each other.
- Webster's New Collegiate Dictionary

Two computers linked together with the TANDEM Remote System work in
conjunction with each other. Both monitors present the same
information, both keyboards can be used to run programs and enter data.
The TANDEM Remote System does what other modem programs cannot do. It
allows you to run virtually all PC-DOS software from a remote location.
You can even run those pesky programs that bypass the operating system
and write directly to the screen memory. TANDEM does what the CTTY
command and modem program SHELL or GATEWAY commands promise, but fail to

The TANDEM system is designed to operate with "Hayes" compatible modems,
or, if you wish, two computers can be directly connected using an RS-
232C "null modem" cable. It is also possible to substitute an H/Z-19
terminal for the "remote" computer, however, the number of application
that can be operated from a terminal is limited; primarily, because the
H/Z-19 has only eight function keys.

The software consists of two separate modules: (1) the TANDEM.EXE
program that runs on the "host" computer, and (2) the TMODEM.EXE program
that runs on the "remote" computer. It is the "host" computer that
actually executes the application and updates the files, your office
computer for example. At some "remote" location, say your home, or
another office, a second computer running the TMODEM.EXE program will
enable to you to control the "host" computer almost as though you were
actually sitting in front of the "host" console.

However, there are some limitations on what TANDEM can do. Because of
the relatively slow transfer of information from the host to the remote
computer, it does not work well with programs that use animation. And,
because the TMODEM.EXE program is especially designed to work with
TANDEM.EXE, it cannot be used as a general purpose modem program to
access bulletin board systems (BBS), or other information retrieval

The following pages detail the operation of the TANDEM Remote System, it
is not difficult to operate and you should have no trouble following the




The "host" is an IBM compatible computer with at least one serial port,
either COM1 or COM2 (or internal modem), and at least 256K bytes of
memory, 640K bytes is suggested. Computers running at 4.77 MHz will
work, but over all performance is greatly enhanced with computers
running at 6 MHz or faster. Either color (CGA) or monochrome (MDA)
video controller cards are acceptable. Any monitor (color or
monochrome) compatible with the video controller can be used. A monitor
with an integral power switch is useful, as the monitor can then be
turned off when the host computer is left unattended.


The "remote" is an IBM compatible computer or H/Z-19 terminal. A remote
computer should have at least 256K bytes of memory and one serial port
(or internal modem). Computers running at 4.77 MHz work just fine, even
small portables can be used. The video system can be either color or
monochrome. Note that the "remote" computer can use a monochrome
monitor, even though the "host" computer uses color; the opposite is
also true.


A "Hayes" compatible modem that uses the "AT" command set and responds
with the standard Hayes command responses is required. Modems operating
at 300-baud will work but the results may be disappointing. A 1200-baud
modem works well with most programs, but modems capable of even higher
baud rates are useful when running some applications. However, some
computers running at 4.77 MHz do not have the "horse power" to handle
modems running faster than 1200-baud.


Modem cables only need three signal lines, "hand shake" signals are set
to a "high" state and ignored. RS-232C pin connections are as follows:

Pin Name Signal
2 TxD Transmitted Data
3 RxD Received Data
7 Gnd Signal Ground

RS-232C cables used for direct connection differ from those used to


connect a modem to a computer and are normally referred to as a "Null
Modem" cable. In this type of cable, pin 2 (Transmitted Data) on one
end of the cable is connected to pin 3 (Received Data) on the other end
of the cable. That is, pins 2 and 3 are cross connected. Signal ground
is connected to pin 7 on both ends of the cable. TANDEM does not use
the "hand shake" signals and they may be left unconnected.



We suggest that you first format two (2) diskettes. Run the FORMAT
program with the /S option to produce a diskette with system files.
Copy your original TANDEM diskette onto one of these newly formatted
diskettes with the operating system COPY command, then place your
original TANDEM diskette in a place for safe keeping. Next, make a
second copy of the TANDEM diskette from the copy you have just made.

One copy of the TANDEM system is for use on the "host" computer, the
other is for the "remote" computer. Both of the diskettes should now
have the following files:

COMMAND.COM Disk Operating System.
TANDEM.EXE The host program.
TMODEM.EXE The remote modem program.
PASSWRDS.DAT Sample pass word file.
TANDEM.DOC Instruction manual.
READ.ME A note to the user.

If you wish, you can delete TANDEM.DOC and the READ.ME files from the
diskettes using the operating system DEL or ERASE commands. Only the
COMMAND.COM, TANDEM.EXE, and PASSWRDS.DAT files are required for the
host (main computer) system. Only TMODEM.EXE is required for the
remote computer system. However, creating three "batch" files, an
AUTOEXEC.BAT, HOST.BAT, and REMOTE.BAT, will make it even easier to
start the TANDEM system and provide for an automatic re-start in case of
a power failure when the host computer is left unattended.

Before creating the three "batch" files, some information is required.
You will need to know:

(1) the serial port number (COM1 or COM2) you are going to use on
the host and remote computers;
(2) the baud rate at which your modems, or serial ports, are going
to operate;
(3) whether the computers are to be connected by modems, or
directly connected with an RS-232C cable;
(4) if you are using a modem, the dialing method to be used (pulse
or tone);
(5) whether your remote is to be a computer running TMODEM or an
H/Z-19 terminal.

Creation of the "batch" files is optional, but you still need to know
system configuration. If you run TANDEM or TMODEM without supplying
this information on the command line, you will be asked to furnish it
before communication can be established between the two computers (or
host computer and terminal).


The TANDEM command line is constructed as follows:

d:>TANDEM port, baud-rate [,H] [,D]

port: Is the COM port number, 1 or 2.
baud-rate: Is the baud rate at which the modem/port runs.
H The optional "H" indicates that the remote is
an H/Z-19 terminal. Default is a computer.
D The optional "D" indicates that the two
computers are directly connected via cable.
Default is a connection via modems.

For example, to invoke TANDEM from the operating system prompt, using
COM port #2, at 1200-baud, with a remote computer, using a modem, the
command line would look like this:

A:>TANDEM 2, 1200

Using COM port #1, at 2400-baud, with an H-19 terminal, connected to the
serial port with an RS-232C cable would look like this:

A:>TANDEM 1, 2400, H, D

Note: the spaces between parameters are optional, however, the commas
separating the fields are required.

The TMODEM command line is similar to the TANDEM command line. It is
constructed as follows:

d:>TMODEM port, baud-rate [,P] [,D]

port: Is the serial port number.
baud-rate: Is the baud rate of the serial port/modem.
P The optional "P" indicates that pulse
dialing rather than tone dialing is
to be used. Default is tone dialing.
D The optional "D" indicates that the two
computers are directly connected via cable.
Default is a connection via modems.

For example, using COM port #1, at 1200-baud, with tone dialing, via

A:>TMODEM 1, 1200

Using COM port #2, at 2400-baud, with pulse dialing:

A:>TMODEM 2, 2400, P

Using COM port #1, at 9600-baud, directly connected via RS-232C cable
(Note: dialing method is not applicable when directly connected):

A:>TMODEM 1, 9600, D


As with the TANDEM example, spaces between parameters are optional, but
commas are required to separate fields.

Using the same command line format, we can now generate a "batch" file
called HOST.BAT. This file can be created with an ASCII text editor or
using the operating system COPY command. To create HOST.BAT using the
COPY command, enter the following:

TANDEM 2, 1200, H, D

The symbol ^Z is entered by pressing the "Z" key while holding down the
"Control" key. Refer to the DOS manual for additional information on
creating "batch" files using the COPY command.

Using the same procedure, create a REMOTE.BAT file:

TMODEM 1, 1200, P

Having created the two "batch" files, we can now invoke TANDEM by simply
typing HOST at the operating system prompt on the host computer. And,
we can invoke TMODEM by typing REMOTE on the remote computer.

On the diskette you are going to be using on the host computer, it is
suggested that one additional "batch" file be added. Create an
AUTOEXEC.BAT file as follows:


Note: "d:" is the disk drive specification, usually "A:" and "\path\" is
the directory where COMMAND.COM will always be available. FAILURE TO
to your operating system manual for more information on the SET COMSPEC

The diskette with the AUTOEXEC.BAT file should be used to boot the
TANDEM host computer system. It should be left in the boot drive at all
times, especially when the host system is left unattended and there is a
chance of a power failure. TANDEM does not, normally, write on this
diskette, therefore, it can be protected with a "protect tab."

If you wish, you may add additional commands to the AUTOEXEC.BAT file.
For example, you may wish to use one or more of the popular memory
resident programs. Memory resident programs should be loaded before
TANDEM, therefore, they should be inserted in the AUTOEXEC.BAT file
prior to the TANDEM command line.



Passwords are used to protect the TANDEM system from unauthorized
intrusion. The PASSWRDS.DAT file must be present when TANDEM is
started. It contains a list of, up to ten, passwords that are composed
of any printable ASCII characters. All of the following examples are
valid passwords:


Note that JOHN and JOHN SMITH are two different passwords and will not
be confused. When you sign on the system, passwords must be entered
exactly as they appear in the PASSWRDS.DAT file.

The PASSWRDS.DAT file can be created using the operating system COPY
command, or your favorite ASCII text editor. WordStar document files
are not acceptable and will not work. A sample PASSWRDS.DAT file is
included on your distribution diskette as an example; it should be
replaced with a list of passwords you invent.

The password system works like this: When a remote user calls the host
system, after contact is established between the two computers, the host
computer will request that you enter a password.


Enter one of the passwords from the PASSWRDS.DAT file, followed by a
RETURN (or ENTER). If you make a mistake (typing error), the system
will respond with "TRY AGAIN". You have three shots at getting it
correct, then you're out! After the third attempt, TANDEM will simply
hang up the phone. This should prevent unauthorized persons from just
trying random words to get into your system. If no characters are typed
for 20-seconds, TANDEM will assume no one is there and hang up the




First boot the host computer system using the diskette with the
AUTOEXEC.BAT and HOST.BAT files (see GETTING STARTED), or, if you
prefer, just type TANDEM at the operating system prompt; you will then
be asked to furnish the missing parameters - COM port, baud rate, etc.
The TANDEM program will initialize the system and then display the
configuration setup for a few seconds. The monitor screen will then
clear, even the cursor will not be visible. If you are going to leave
the host system unattended and your monitor has a power switch, you may
turn the monitor off.

If you have booted the system with a floppy diskette, we suggest you
leave this diskette in the drive. If you replace it with another
diskette, the replacement must have a copy of COMMAND.COM on it, or you
must provide the operating system with a path to COMMAND.COM, otherwise,
TANDEM will not function correctly.

At the remote location, boot the remote computer and run the REMOTE
command (see GETTING STARTED). Or, you may just type TMODEM at the
operating system prompt; you will then be asked to furnish the missing
parameters - COM port, baud rate, etc. The remote modem program will
then ask you to enter the phone number to be dialed. The number you
enter will be sent to the modem exactly as you enter it. For example,
if you enter: (229) 776-4321, then "(229) 776-4321" will be sent to your
modem. Most modems accept the punctuation, check your modem manual to
be sure. TMODEM will then wait for your modem to respond with a
"CONNECT" message.

Sometimes, because of noise on the phone lines, the "CONNECT" message
may be garbled. If this happens, press the ESCape key, enter the
letter "C" and a RETURN. This will force the TMODEM program to continue
as though the proper "CONNECT" message had been received from the modem.

Pressing the ESCape key before the modem responds with "CONNECT" will
cause the phone to hang up. You may enter another number, or re-dial
the same one by entering the letter "R" and a RETURN.

To exit from TMODEM without establishing contact with the host computer,
you can press the ESCape key 4-times (your computer will "beep").

Once contact has been established with the host computer, TANDEM will
ask for a "PASSWORD:", (see the section on PASSWORDS). Enter the
correct password and TANDEM will sign on with the "TANDEM:>" prompt.

From the TANDEM:> prompt, there are a number of special TANDEM commands
you can run. Each of these commands is discussed in the following


CLS - Clears the screen and re-displays the TANDEM:> prompt.

DIR - Displays the current directory or you may specify a disk drive and
path name. For example: TANDEM:>DIR B:\WORK\ would display the
directory for disk drive B:, subdirectory \WORK\.

TYPE - Displays the file specified (e.g. TYPE TANDEM.DOC) on the screen;
pausing after each page. Press ESCape to terminate the TYPE command, or
any other key to view the next page.

DOS - Loads a second copy of COMMAND.COM into memory and starts it
running. A message reminds you to enter the EXIT command at the DOS
prompt to return to the TANDEM:> prompt, you must do so to sign off the
system or use the TYPE command. At the DOS prompt, you can use any
command and run almost any program. There are, however, a few programs
that will not run correctly, or even worse, lock up the system. See the
section on PROBLEM PROGRAMS. With the exception of three keys, the
remote computer keyboard works just like the host console keyboard. The
LOCK), and SHIFT-PrintScreen keys. The SHIFT-PrintScreen key will cause
the monitor screen to be printed on the "remote" computer's printer, not
the "host" computer's printer. The PAUSE key only affects the "remote"
computer. The BREAK key has no affect at all. When you are through
with the DOS system, always return to the TANDEM:> prompt and issue a
BYE or SHUTDOWN command.

BYE - Causes TANDEM to hang up the phone and recycle and await the next
caller. DO NOT FAIL TO RUN THE "BYE" COMMAND (or SHUTDOWN command, see
below). If you terminate the remote modem program without giving the
BYE command, your computer is left wide open to anyone who comes along.
They won't even need a password! The BYE command will cause the remote
modem program to terminate.

SHUTDOWN - This command provides a way to terminate TANDEM on the host
computer from a remote location. TANDEM will ask; "Are you sure ?", if
you answer with a "Y" for yes, TANDEM will close down. ONCE A
THE "HOST" COMPUTER. This command should only be given when you are
certain that no further calls will be made to the "host" computer.

Normally, either the BYE or SHUTDOWN commands will cause the TMODEM
program to exit to the operating system prompt. If, for some reason, it
is necessary to exit TMODEM without issuing BYE or SHUTDOWN, then hold
down the ESCape key (or press it at least eight times), the computer
will beep several times before exiting....


After the booting TANDEM and the screen clears, you may still operate
the host computer from the host console. You do this by typing "LOCAL"
and a RETURN on the host keyboard.


TANDEM will, as it does for a remote call, ask for a PASSWORD:. Enter a
valid password and TANDEM will display the TANDEM:> prompt. Operation
is just as though you had called in from a remote location. For calls
to be accepted, you must sign off using the BYE command.

The host computer keyboard is always active, even when a remote user is
operating the system. This feature allows two people to run a program
"in tandem."


TANDEM can be operated using a remote H/Z-19 terminal instead of another
computer running TMODEM. Note, the system must be started using the
command line "H" option. Operation is essentially the same, except that
the terminal will only display the first 24-lines of data showing on the
host monitor. Also, since the terminal keyboard does not have the
ALTernate key, we have substituted a combination of ESCape, CONTROL-{A
thru Z} to serve as ALTernate-{A thru Z}. Even so, many programs cannot
be controlled from a terminal because it has only eight function keys.


Two computers can be directly connected by an RS-232C null modem cable
(see the section on EQUIPMENT). Since no modems are involved, dialing
the phone is not possible, in fact, meaningless. However, password
checking is still in force. Otherwise, TANDEM operates exactly as it
does through a modem and the phone lines. You may, of course, use one
of the higher baud rates. Running at 2400-baud works very nicely, 9600-
baud is even better; however, some computers are incapable of supporting
9600-baud --- try it to determine if any problems exist.



Most application programs will run under TANDEM without problems, even
those pesky programs that write directly to the screen memory. However,
there are some exceptions, generally programs that fall into one or more
of the following categories:

1. Programs that manipulate the COM ports, such as another modem
program. It is okay for a program to use a COM port, so long as it is
not the one TANDEM is using.

2. Programs that assume direct (and absolute) control of the keyboard.
Few programs do this. The QuickBASIC compiler editor is an example of
one that does. The result is a locked remote system --- the "host"
keyboard still operates.

3. Programs that use dot graphics. TANDEM does not support dot
graphics (character graphics are okay). Running one of these programs
causes strange things to happen to the remote screen. Returning to the
operating system prompt clears the problem.

4. Programs that use animation may not work very well. This is due to
the relatively slow transmission of data from the host to the remote.


1. The QuickBASIC compiler editor.
2. Zenith's version of GW-BASIC.


1. Microsoft's MASM (assembler).
2. GW-BASIC (not Zenith's version).
5. RHM (Right Hand Man).
7. XDIR.
9. Z80MU (Z-80 emulator).
10. Ellis FORTRAN compiler.
12. COPY, TREE, and other DOS commands.

Let us know what programs you have ran successfully and we will include
them in future documentation.



Wouldn't it be a dull world if there were never any problems? If the
lack of problems makes for a dull world, then computers will never be
boring. If you have a problem with TANDEM, we suggest the following
points to check:

1. Check the equipment. Could be someone unplugged the RS-232C
cable or something like that.

2. Is your modem on the COM port you think it is? Have you
selected the proper baud rate?

3. Recycle your equipment. Some modems will hang up for no
apparent reason, turning them off and on will clear things.

4. Is the printer turned off? Trying to print with it off will
sometimes hang the system.

5. Are there diskettes in all disk drives and the doors closed?
Some systems will hang if you try to access a drive that can't run.

6. From the remote system, it may appear at times that TANDEM does
some strange things with the display screen. This usually happens
during scrolling of the screen or when menus pop-up. Be patient and
things will eventually settle down. If someone picks up a phone on the
modem line, the resultant noise may cause the screen to blow up! Exit
the program you are running and issue a CLS command.

7. If you should get an error message from TANDEM, we don't think
it can happen, then TANDEM will do its best to lock the system. This is
done to prevent unauthorized access to your computer.

8. If your problem is none of the above, take a few moments and
drop us a line and tell us what you were doing and what happened. We'll
do our best to help you solve the problem.



We know that The TANDEM Remote System is not perfect. We will continue
to work to improve it, but we also need your help. Your suggestions
steer us in the right direction and even help to squash those nasty

If you have a suggestion or a problem, let us hear from you. Write to
the following address:

Louis E. Wheeler
P.O. Box 888
Oceano, CA 93445



  3 Responses to “Category : Network Files
Archive   : TANDEM2X.ZIP
Filename : TANDEM.DOC

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