Black Box MD1640A, MD1641A manual Appendix G V.25bis Operation

APPENDIX G: V.25bis Operation

added to the Delayed Number list and the oldest existing number added to the Forbidden Numbers list. Numbers are removed from the Forbidden Numbers list by after a certain time has past (also by country regulation).

Some country regulations have numbers remain on the Forbidden Numbers list permanently. The Delayed Number and Forbidden Numbers lists are eight numbers long (20 characters each).

V.25bis Operation

Operation in V.25bis mode is similar to AT command mode in that certain DIP-Switch functions are important to its operation. V.25bis does not include any speed detection for asynchronous mode, so when you are giving commands, you must stay in your initial speed (i.e., if you change your terminal speed while entering an AT command, you will get no responses). In synchronous mode, the modem supplies the clock, so the synchronous terminal “knows” the speed.

You must be in V.25bis mode for the commands described here to function. Most AT commands will also function, except those associated with dialing such as ATD, ATN, ATO, and ATU. To get into V.25bis mode, you type AT$V1. At this point your modem does no more speed or parity detection (things associated with asynchronous operation). To get out of V.25bis mode and back into AT command mode, enter AT$VO. The AT$V2 command allows you to run one V.25bis command from AT command mode without leaving AT command mode.

There is no command to select between asynchronous and synchronous V.25bis operation. The position of DIP-Switch #12 selects between modes. For synchronous mode, DIP-Switch #12 must be UP, and the AT command mode enabled.

Another asynchronous mode concern is the problem of connecting at a different speed than the speed at which the serial port is set. If your modem port speed is different from the serial port speed, you must either:

1)Enable speed conversion and have flow control on, or

2)Enable connect responses (with the ATX1 command) and change the serial baud rate after receiving a connect message.

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