Adding and configuring modems

Problems dialing in

You may experience one of the following problems on dialing in:

Modem does not answer the phone

If the modem does not answer the phone:

  1. Verify that the modem control port is enabled. To do this, the corresponding non-modem control port should be disabled, before enabling the modem control port. Refer to ``Configuring a modem without using the Modem Manager'' where an example of disabling a port is given. Enable a port using the -e option of sacadm(1M).

  2. Verify that the modem is configured to auto-answer. Check your modem switches. If the modem has a ``Direct'' entry in /etc/uucp/Devices (for the /dev/term/00m device, for example) enter:

    cu -l term/00m

    Then, use the ATS0=1 command to tell the modem to answer the phone on the first ring. (Remember to enter AT&W to save modem settings.) The Monitor feature in the Modem Manager controls ATS0. This determines the number of rings before a call is answered.

  3. Verify that the DTR (Data Terminal Ready) line is connected from the computer to the modem. Make sure that pin 20 is connected. Pins 2, 3, 7, 8, and 20 are required for modem communication.

  4. Make certain the ACU entry for this modem in the Devices file precedes any ``Direct'' entries for the port or the non-modem control counterpart.

Modem answers, but hangs up

If the modem answers, but hangs up immediately upon connection:

  1. If the modem is set to auto-answer and to detect DTR, check to see that the DTR line is asserted.

  2. Verify that the modem control port is enabled. See ``Modem does not answer the phone'' for details of how to do this.

  3. Verify that the cable is correct. If you are using a straight-through cable with at least pins 2, 3, 7, 8 and 20 connected, verify that pin 20 (DTR) is properly connected.

  4. Check to see if the modems have data compression or error correction modes set. After a connection is established, modems that support special error correction or compression protocols attempt to negotiate which of these protocols to use. If the other modem is programmed not to use any of these modes (or does not support them), it may misinterpret this negotiation as actual user input. In general, modes such as MNP4 or v.42bis should only be enabled when connecting with a modem with the same modes enabled. Check the documentation for your modem.

Garbage or loose cable

If the console displays a message like

   Garbage or loose cable on /dev/term/00m, port shut down
when a call comes into the modem:

  1. Verify that your modem is not set to echo back data or send command responses. If the modem is not set up this way, it may be sending a RING signal to indicate that the phone you are calling is ringing. Because the CD signal is not active, the serial driver interprets this as random data on the serial line. The appropriate Hayes-compatible modem command is ATE0Q1.

  2. If you have an internal modem and the above options do not eliminate the error message, your modem may be incompatible. Contact the manufacturer to see if a fix is available. If no fix is available, you may need to replace your modem with a standard Hayes-compatible external modem.

Modem answers, but no login prompt is displayed

If the modem answers, but does not display a login prompt:

  1. Verify that the CD line is being asserted by the modem after the modem has answered the phone. Check the switches on your modem or, if your modem is Hayes-compatible, use the AT&C1 command. (Remember to enter AT&W to save modem settings.)

  2. Make sure that the port is enabled. Refer to ``Modem does not answer the phone'' for details of how to do this.

  3. Verify that the port is set up correctly using the sacadm -l command which lists the port monitors on the system, and then pmadm -l to list the port monitor services.

Screen displays a series of login prompts

If the screen scrolls uncontrollably when you log in, usually displaying a series of login prompts, verify that only the modem device is enabled. If the non-modem device is enabled, disable it. Refer to ``Configuring a modem without using the Modem Manager'' for an example of disabling a port.

System displays meaningless characters

If the system displays the login prompt, but no password prompt, or meaningless characters are displayed after the login prompt, verify that the line settings are correct:

  1. Determine the serial line settings on the system that you are calling. The standard settings that cu uses are 8 data bits, one stop bit, and no parity.

  2. If you are dialing into a UNIX system, look at the settings used by the port monitor using

    pmadm -l

    to verify that the ``pointer'' into the /etc/ttydefs file is correct. A typical line looks like this:

    ttymon1	ttymon	term/00m	u	-	login	/dev/term/00m \
    boPhr 0 auto 60 115200_8N ldterm,ttcompat login:  - - - -  #
    This line uses /dev/term/00m, is set for bi-directional, uses a login and is set for 115200 baud, 8 bits, no parity. The 115200_8N refers to an entry in /etc/ttydefs.

    The serial line characteristics may not match between the stty settings defined in the third field of the selected ttydefs entry. Change the setup for the port to 8 data bits, one stop bit, and no parity.

© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 22 April 2004