Compaq 281862-002 manual Computer to Modem Serial Port Speed, Data Carrier Detect DCD Operation

6-6Additional Modem Information

Computer to Modem Serial Port Speed

Some modems have a configuration option that controls whether the DTE serial port interface is fixed at a predetermined baud rate or changed dynamically based upon the modem to modem connect rate. In “floating DTE” mode, the Computer to Modem speed is automatically adjusted based upon the Modem to Modem negotiated baud rate. For IRC to operate properly, the DTE (server to modem) baud rate must be set to fixed. For many enhanced high-speed modems, this is the default setting following a modem reset. This configuration command must be appended to the IRC initialization string if your modem does not default to the fixed setting (particularly a problem with U.S. Robotics modems). Improper setting of the DTE speed configuration results in the inability to obtain a login prompt from IRC after establishing a connection. (See Appendix C, “Troubleshooting”). Refer to your modem documentation for more details. Modem vendors differ on the specific nomenclature used to refer to this setting. Look for terms such as “Fixed/Floating DTE,” port-rate adjust, speed conversion, or buffered mode. Look for the &B or \J setting in your modem’s AT command reference.

Data Carrier Detect (DCD) Operation

Most modems have a configuration option that controls the assertion of the DCD serial port interface signal. Typically DCD can be configured so that it is either always asserted (DCD Override) or only asserted when connected to another modem (DCD Normal). For Integrated Remote Console to function properly, the modem must be configured to assert DCD only when a carrier is established with another modem. Improper setting of this configuration option results in the inability to obtain a login prompt from Integrated Remote Console after establishing a connection. The &C AT command controls this setting in most modems. Since modem vendors differ with respect to the default setting of this configuration option, appending an &C1 to the Integrated Remote Console initialization string ensures proper DCD operation.