3Com 980/000048/001 manual Modem DTE Connection, Modem does not accept or echo back AT commands

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3-2 CHAPTER 3: TROUBLESHOOTING

Modem - DTE Connection

Modem does not accept or echo back AT commands

Check that the cable between the serial port of the DTE and the modem is a standard RS232 cable. If the cable is bad, replace it. (Null modem cables, also known as cross-over cables, do not work in this application).

A limited number of dumb terminals require DCD before they can talk to the modem. If this is the case you have to use a breakout box to raise DCD to the terminal. You can then configure the modems to force DCD using the AT&C0 command.

Check that the character echo command is enabled using the ATE command.

Check that the DTE dialler type configuration option is set to AT. Refer to the AT&M or AT&Q command description.

Check that the response codes configuration option is enabled using the ATQ command.

Make sure that all AT commands are terminated with a carriage return.

Check that the ASCII value of a carriage return matches what is used by the DTE and the modem (defined using S-Register S3).

Check that the DTE and modem are using a compatible character format. Valid formats include 8 data bits with no parity, or 7 data bits with even, odd, mark or space parity.

Check that the DTE’s data rate is supported by the modem.

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Contents Accessbuilder Triple Modem Module User Guide 3Com Corporation 5400 Bayfront Plaza Santa Clara, California Important Safety Information Wichtige Sicherheitshinweise ’INFORMATION DE Sécurité Importante Page Contents Modem Specification and Interface PIN Assignments Index Limited Warranty FCC Class a Verification Statement Page How to Use This Guide This table shows where to find specific informationAbout this Guide IntroductionText conventions used in this guide are ConventionsIcon conventions that are used throughout this guide are Additional Safety Information Keep the unit away from radiators and heat sourcesAbout this Guide Triple Modem Module Principal Features Support for dial-up transmission protocolsImplementation of V.32terbo Triple Modem Module Typical Applications Modem Connections To The Central SitePack Contents Checklist Registering Ownership of your Triple Modem ModulePre-installation Requirements Triple Modem Module Installation and Operation OverviewInstalling The Module Installing the Rear Card Installing The Rear CardInstalling the Front Card Example of Installing a Front CardConnecting the Cables Front Panel LEDs Front Panel LEDs Installation and Operation Modem Health TroubleshootingTroubleshooting Guide Modem does not accept or echo back AT commands Modem DTE ConnectionModem Telephone Line Connection Troubleshooting Perform a local analogue loop test Private-line Operation Dial Backup OperationOn-line Operation Interface PIN Assignments Modem SpecificationTransmitter / Receiver Specifications Autodial Autoanswer Physical Description ProtocolsApprovals Information General Approvals RequirementsAll the other apparatus shall comprise only Appendix a Modem Specification and Interface PIN Assignments Ringer Equivalence DTE Port Pin Assignments 21/V.1124/V.28 35/V.36 Pstn Port Cable Pin Assignments Private Line Port Cable Pin Assignments On-line Technical Services 3Com Bulletin Board ServiceWorld Wide Web Site Call the telephone number nearest youSupport from Your Network Supplier Support from 3Com Returning Products for Repair Appendix B Technical Support Index NumericsSend LED Limited Warranty 408 764-5000 3/18/96 How to Identify and Resolve Radio-TV Interference Problems