Appendixes

S-Registers

Alphabetic Command Summary

Flow Control Template

Result Code Meanings and Sets

Technical Information

V.25 bis Reference

ASCII Chart

Fax Information for Programmers

Viewing LEDs

Regulatory Information

Glossary

Courier 56K Corporate Modem Command Reference

Troubleshooting

This chapter explains how to troubleshoot the Courier 56K Corporate modem. This chapter is divided into these sections:

Problems that occur before connecting.
Problems that occur after connecting.
If you still have problems.

Problems That Occur Before Connecting

No response to AT.

For Windows users, make sure that you set the correct COM port and IRQ in your communications software and, if applicable, in Windows Control Panel - Ports.

Make sure that your communications software is in Terminal mode.
Be sure that your communications software is set to the correct bit rate and word length (7 bits with or without a parity bit, or 8 bits and no parity).
Check that DIP switch 8 is ON, for "act on AT commands." If DIP switch 8 is OFF, power off the Courier 56K Corporate modem, set the switch ON, and power on the Courier 56K Corporate modem again. Then try typing AT Enter again.

Make sure that verbal result codes (status messages) are enabled. Send these commands to the Courier 56K Corporate modem:

For your modem to	Command
Enable message display	ATQ0
Display verbal messages	ATV1

Review your communications software manual to see what Carrier Detect (CD) operations your software requires. Then see the chapter about Controlling EIA-232 Signaling.
Although it is a rare condition, check whether your computer is reversing the send/receive functions at the EIA-232 interface. Refer to your computer's documentation.
Check your serial cable to make sure it is not a NULL modem cable.

The Courier 56K Corporate modem won't dial.

You may need to change the DTR setting at the Courier 56K Corporate modem. If so, see the Controlling EIA-232 Signaling chapter in this guide.
Make sure that the phone line from your wall jack connects to JACK port of the Courier 56K Corporate modem.
Make sure the Courier 56K Corporate modem is connected to a standard analogue phone line and not to a digital system (typically found in offices and hotels).
If the Courier 56K Corporate modem responds NO DIAL TONE when you attempt to dial, make sure that the phone line is connected to the JACK port on the back of the Courier 56K Corporate modem.

If you hear a dial tone when the Courier 56K Corporate modem tries to dial but it quickly returns off hook and reports NO DIAL TONE, try adding X5 to the dial string. For example, send ATDTX5 5551212 to the modem. The Courier 56K Corporate modem will ignore dial tone detection.

Double characters are appearing on your monitor.

This is a signal that both the Courier 56K Corporate modem's local echo and your software's local echo are on.

Type the command to turn off your online echo (ATF1) or turn your communications software's local echo off (refer to your software's documentation).

After you dial, the Courier 56K Corporate modem reports NO CARRIER and then hangs up.

Try increasing S7 and decreasing S9 to allow more time for the connection.
Try calling a different device. If you are trying to connect to an older modem at 2400 bps or less, it may not support error control. Try sending AT&M0, and then try the call again. Reset the Courier 56K Corporate modem (send ATZ) after you finish the call.

You hear ringing, but the Courier 56K Corporate modem won't answer.

Look at the DTR LED to make sure that your terminal or computer is sending a DTR signal via the EIA-232 interface.
Send ATI4 to the Courier 56K Corporate modem and check that S0 is set to a value higher than 0. Also, check that DIP switch 5 is OFF.
Set &F1 and S0=1, then try again.

The Courier 56K Corporate modem acts as though a data link has been established, but no call was received.

Carrier Detect (CD) may be overridden (with &C0), but your system may require that the override be turned OFF (with &C1). Review your communications software manual to see what CD operations are required.

The Courier 56K Corporate modem behaves as if Enter were pressed when you don't press any keys.

Your software may be misreading signals from the Courier 56K Corporate modem when the Courier 56K Corporate modem sends a Carriage Return and a Line Feed before and after the RING and CONNECT messages. Sending the Quiet mode command, ATQ1, should solve the problem.

Problems that Occur After Connecting

Your screen displays random or "garbage" characters.

Make sure that the Courier 56K Corporate modem is set to the same bit rate, word length, parity, and number of Stop bits as the device to which you are connecting.

If the settings are correct, the problem may be with the phone line. Try the following measures:

Place the call again. The phone company routes even local calls differently each time you call.
Call a different device to see if the problem persists. The problem may be with the device you first tried to call.

If the modem is set to a fixed serial port rate (&B1) and your software is fixed at 19.2K, 38.4K, 57.6K, or 115.2K bps, the reason may be one of the following:

Your computer may not support the higher serial port rate. If this is the case, fix your software rate at 9600 bps.
If you use memory-resident programs (TSRs-Terminate and Stay Resident programs) or disk-caching programs, they may be interfering. Try disabling them before you run your communications software.
Check that your software and the Courier 56K Corporate modem are set for the same kind of flow control, either hardware or software. Some communications programs also require that you disable the type you are not using.

Many CRC errors are being received.

Send AT&F1 to enable hardware flow control and other optimised settings.
Try a different file transfer protocol (use ZMODEM if it's available to you).
If you use memory-resident programs (TSRs-Terminate and Stay Resident programs) or disk-caching programs, they may be interfering. Try disabling them before you run your communications software.

Mainframe computer keeps dropping your connection.

You must turn off the Courier 56K Corporate modem's result codes and character echo (ATQ1E0). The modem at the mainframe also needs to be set to ATQ1E0.

Bad faxes or can't fax

Make sure the fax software is set to use Class 1 fax. Refer to your fax software's manual.
If you use memory-resident programs (TSRs-Terminate and Stay Resident programs) or disk-caching programs, they may be interfering. Try disabling them before you run your communications software.

Both devices exchange carrier signals but fail to establish a communications link

Make sure the Courier 56K Corporate modem is in the correct mode, fax or data, depending on whether the connection is to be made with a facsimile device or a data device.

Refer to the Modes of Operation chapter in the Content section for information on switching between Fax and Data modes.
Make sure the proper bit rate, word length, parity, and number of Stop bits have been selected.
Synchronous operations: review the instructions in the Dedicated/Lease Line and Synchronous Applications chapter of the Content section. If you've configured the Courier 56K Corporate modem correctly, the problem may be with the synchronous adapter or with the system you're trying to call.
Send ATI4 and check to see that your modem is at the correct Bn setting to connect with either an HST modem (B1 setting) or “V.” modem (B0 setting).
Make sure that your Courier 56K Corporate modem's connection rate setting, &Nn, is correct for the call. If the connection rate is locked at a speed (&N1-&N14) different from the calling modem's, the Courier 56K Corporate modem hangs up. The default setting of &N0, variable link operations, allows the two modems to negotiate the highest possible connection rate.
If your modem is attempting to answer a V.32 call, you may need to lengthen the extra V.32 answer tones. Refer to the Alphabetic Command Summary appendix in this guide under S28.
If you are attempting to make a connection using HST modulation, make sure that the modem at the other end of the line is HST compatible, V.32 terbo compatible at 14.4 Kbps, V.32 compatible at 9600 bps, V.22 bis compatible at 2400 bps, Bell 212A-compatible at 1200 bps, or Bell 103-compatible at 300 bps.
If none of the above corrects the problem, it's likely that the quality of the phone connection is poor. The variable quality of phone line connections may be due to any number of conditions in the phone service's equipment or the current environment. Try several calls, and if you still can't get through, try calling another device. If the second device accepts your call, the problem may lie with the device you first tried to call.

Errors during software download

Try performing the XMODEM file transfer at a slower serial port rate. If your computer doesn't have a 16550 UART, set your communications software to use a slower serial port.

If You Still Have Problems

The problems described above are by far the most common ones that users encounter. If the suggestions we've given don't clear up your difficulties, try the following:

Review this guide carefully to see if you've missed something.
Call or visit your dealer. Chances are that your dealer will be able to give you the assistance you need.
If your dealer can't help you, call the USRobotics technical support line.
If you must return your Courier 56K Corporate modem to USRobotics, the Service Representative you talk with will give you a Service Repair Order (SRO) number. Products without an SRO number will not be accepted.
If you do return the Courier 56K Corporate modem to us, please follow these procedures:

In the United States:
- Ship the unit, postage pre-paid, in its original container. If the original container is not available, pack the unit carefully in a strong box of corrugated cardboard with plenty of packing material.
- Be sure to include your SRO number inside the package, along with your name and address. Put your return address and your SRO number on the shipping label as well.
Ship the package to the following address:

USR-Walnut
528 Spanish Lane
Walnut, CA 91789

Note: USRobotics will not accept packages sent COD, so be sure to send the modem postage paid.

USRobotics will repair or replace your Courier 56K Corporate modem and return it to you via United Parcel Service.

Outside the United States:

Follow the instructions provided by the USRobotics techncial support representative.

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