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Contents:
Attaching A Modem To A Mainframe
UNIX, XENIX, VMS and ULTRIX
Attaching a modem to a mainframe computer can be tricky. There are so many different varieties of each mainframe operating system that there is no one setup that will work with them all. This document describes the general configuration requirements of most non-DOS operating systems. Consult your operating system's documentation for more specific information.
Installing a modem on a mainframe (or any non-DOS operating system) requires these steps:
Configuring the mainframe serial port.
Connecting the modem to the mainframe.
Configuring the modem for the mainframe. Configuring The Mainframe Serial Port
The first step involves configuring the serial port you want to use for the modem. You'll probably need to read the manuals or contact the manufacturer or the serial port for serial port configuration information.
Configure the serial port for whichever is lower: the serial port's maximum speed or the modem's maximum speed. Calling modems can never connect at a speed faster the the modem-to-computer connection, so always use the fastest possible speed. For example, if a 9600EX is connected to a computer at 4800 baud, 4800 is the fastest rate at which any modem can connect. Here are the recommended settings for Intel modems:
| 14.4EX |
57600 |
| 9600EX |
38400 |
| 2400EX MNP |
4800 |
| 2400EX |
2400 |
Also, you must enable CTS/RTS flow control on the serial port if you want to allow "Reliable" connections. Reliable connections use MNP or CCITT error correction and data compression protocols to ensure accurate data transfer and maximum through-put. Connecting The Modem To The Mainframe
Once the serial port is configured, you need the correct cable to connect the serial port to the modem. Document 4300 shows the correct cable configuration. Basically, the cable should connect straight through on pins 2 through 8, 20, and 22.
Configuring The Modem For The Mainframe
Before connecting the modem to a mainframe computer, you must configure the modem using a dumb terminal or a personal computer. However, make sure the serial port on terminal (or PC) you use to configure the modem is set to the same baud rate as the mainframe serial port. If the baud rates are different, the modem will not work on the mainframe.
There are many possible configuration commands you could use, but Unix/Xenix documentation often suggests this string:
AT&FE0Q1S0=1&C0&D0\J0\N3\Q3&W
Intel does not guarantee this command will work with all operating systems, but you can use it as a basis to begin modem configuration. Here is a description of the commands in the configuration string:
| Modem Command |
Function |
| AT |
Attention code. Must be first in line |
| &F |
Resets modem to factory default settings |
| E0 |
Modem doesn't echo commands back to host |
| Q1 |
Modem doesn't display result codes |
| S0=1 |
Modem answers after 1 ring |
| &C0 |
Carrier Detect signal always on |
| &D0 |
Ignore DTR signal from mainframe |
| \J0 |
Disable serial baud rate adjust |
| \N3 |
Auto-reliable mode (MNP active) |
| \Q3 |
Bi-directional CTS/RTS flow control |
| &W |
Save configuration to non-volatile RAM |
If you're receiving data from a mainframe and losing characters, there's a good chance that the cable and/or the operating system doesn't have CTS/RTS flow control enabled. Refer to your reference manual for the operating system, contact your system administrator, or contact the manufacturer of the operating system to find out how to enable CTS/RTS.
Some operating systems require that the Data Carrier Detect (DCD or CD) signal remain "ON" at all times. The command AT&C0&W turns on DCD permanently. Make sure your serial cable has a wire connecting the modem's DCD signal (pin 8) to the computer's DCD signal.
If you still have problems using the modem after trying these suggestions, contact the manufacturer of the operating system and ask them how to install a Hayes 2400 baud modem. Follow the instructions except, if you're using a 9600EX, set the serial port baud rate to 38,400bps.
When the modem is correctly connected and configured, these LEDs on the front panel should be lit.
| AA |
Auto Answer |
| TR |
Terminal Ready | Attaching An External Modem To A Dumb Terminal
It is relatively simple to attach an external modem to a dumb terminal. Here's how:
- Set the terminal's serial port speed to whichever is lower: the serial port's maximum speed or the modem's maximum speed.
| 14.4EX |
57600 |
| 9600EX |
38400 |
| 2400EX MNP |
4800 |
| 2400EX |
2400 |
- Set the terminal's word length, stop bits, and parity to match the system you plan to call. If in doubt, set the serial port for:
- 7 data bits, 1 stop bit, Even parity
- Plug the modem's power supply into an outlet and plug the other end into the modem. Plug one end of the the modem cable into the terminal and the other into the modem.
- Turn on the modem and then the terminal.
- At the terminal, type 'AT' then press the Enter key. The modem should respond by printing "OK" on the terminal's screen.
- You may now enter ATDT followed by the telephone number of the system you want to call. Some Intel external modems allow you to permanently store phone numbers in the modem's non-volatile memory. Read your modem's command guide for more information.
This applies to:
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