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Configuring USRobotics Modems For use under Unix-Type Systems

Applies to USRobotics Sportster and Courier modems

In order to configure a USRobotics modem for use with your Unix based system, you will need to know the following things:

  • Will the modem be used for dial-up, or dial-up and dial-out (UUCP, cu, tip, kermit, etc.)?
  • Is the port defined as using Hardware (RTS/CTS) or Software (XON/XOFF) flow control?
  • Will the port speed (DTE speed) be locked or defined at a constant speed, or will it change to match the modem connection speed(autobaud)?
  • How many data bits(word length), what parity, and how many stop bits is the Unix port configured to use? (Usually 8, None, 1; OR 7, Even, 1) .
  • Is the port the modem will be attached to considered a modem control port? (i.e., does it support/monitor the following RS232 pin signals: DSR, CD, DTR?) Also, does the serial cable have at least 9 pins connected through the cable (1-9 on a DB9 connector or 2-8 and 20 on a DB25 connector)?
  • How many rings do you wish the modem to answer on?
  • Do you wish to configure the modem to use error correction, data compression, and/or any additional features?

You will also need a terminal, PC, or Macintosh, with communication software to initially configure the modem.

Configuring the Modem:

  • If you have a Sportster modem, configure dip switches 3, 7, and 8 Down or On.
  • If you have a Courier modem, configure dip switches 3, 5, 8, and 10 Down or On.
  • If you have a Worldport, disregard.
  • Attach one end of the serial cable to your modem and the other end to your terminal or PC.
  • Configure the terminal or communications software setup to match the settings of the Unix system's getty or port monitor with regard to port speed (baud rate), parity, data bits, and stop bits.
  • Enter terminal mode of the communications software if its being used. Type the following:
    and press Control-M on the keyboard. The modem should respond "OK."

Determining What Modem Initialization Command To Use

The modem initialization command will begin with AT&F. Use the following information to determine what additional modem commands should be appended to this command.

  • Flow Control
      XON/XOFF (software) flow control: &H2&I2
      RTS/CTS (hardware) flow control: &H1&R2
    If you're not sure what kind of flow control to use, use &H2&I2. Most Unix type systems default to Software flow control.

  • Port Speed
      Locked port (DTE) speed (=> 19200): &B1
      Port speed matches connect speed (< 9600): &B0
    If you use &B0, your getty or port monitor should not be set at speeds greater than 9600 bps. If you're not sure which to use, select &B1. If the port speed is set lower than the maximum capability of the modem, turn off the high speed ranges with the following commands:
      For V.34 modems with S-Registers that go into the fifties: Add S54=196 (turns off V.34 and V.FC 16800–28800)
      For V.34 modems with S-Registers that go into the thirties: Add S32=28
      All modems: Add S34=7 (disables 14400)
      All modems: Add S27=4 (disables 9600)
      Number of rings to answer on: S0=2 (i.e., answer on 2 rings)

  • Data Compression
      Use V.42 bis or MNP5 data compression &K1
      Use V.42 bis data compression only &K3
      Use MNP5 data compression only &K1S27.5=1
      Use no data compression &K0
    If you're not sure what kind of data compression to use, select &K1

  • Error Correction
      Use MNP or V.42 error correction &M4
      Use MNP only and not V.42 error correction &M4S27.5=1
      Use V.42 only and not MNP error correction &M4S27.4=1
    If you're not sure what kind of error correction to use, select &M4.

  • Other Options
      You're using a modem control port: &S1S13=1
      Dial in only: S2=255

Saving The Settings In Your Modem’s NVRAM

Append &W to your modem init string to write the settings to NVRAM. To verify that the settings are stored in NVRAM, use the following AT command: ATI5.

You are now done created your modem initialization string.
For example: Locked port speed, RTS/CTS flow control, all data compression and error correction, answer on one ring, dial in only, and a modem control port:
World Port 14.4:
AT&F&H1&R2&B1S0=1&K1&M4&S1S13=1S2=255 &C1&D2V1Q1E0Y0 &W0
Type in your modem initialization string and press Control-M. The modem should respond "OK." This does not apply to the Worldport however. With the Worldport modem, you should verify the settings using the ATI4 command, for the result codes or commands will not be shown with this modem.

Now your modem is programmed and you can attach it to your Unix system. Put dip switch number 4 down (ON) and the rest up (OFF). If you also plan on calling out, put dip switch number 8 down, or in the ON position. If you're using a Courier modem, put dip switch number 7 down (ON). If you're NOT using a modem control port, put dip switch number 1 down (ON). Enable the port on the Unix system and you're set!

UNIX Troubleshooting

If you are having trouble receiving calls, perform the following test to determine if the UNIX settings are conflicting with the modem’s.
  • Power off the modem and disconnect it from the UNIX machine.
  • Position DIP switches 1 and 4 down, and put the rest up. Power on the modem.
  • Call the modem. If it answers and connects, then it is a conflict between the UNIX and the modem settings that is causing the problem. You need to verify that you are using the correct settings.

Verifying the modem’s settings

  1. Power off the modem.
  2. Set DIP switches 3 and 8 down.
  3. Access the modem using a communications program and verify the following by typing ATI5:
  4. The baud rate of the modem equals that of the UNIX port.
  5. The proper flow control, either XON/XOFF or RTS/CTS, is selected.
  6. Also, if you are using hardware flow control (RTS/CTS), verify that you have the proper cable.
  7. Remember to reset the modem’s DIP switches before returning the modem to the UNIX machine.
  8. If you are setting your UNIX system to autoanswer and are finding that it is not answering the incoming call, set dip switch 8 up and see if that helps.

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