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Chapter 5 - Command Mode
Fallback Modes When On-Line #F
If line conditions deteriorate, the modem automatically drops its transmission speed (“fallback”). The
#F command controls the different ways the modem falls back. During operation, if the error rate
becomes too great, the modem performs a retrain. If after the retrain, the error rate is still too high for
33600 bps (19200 bps for 1932 models, 14400 bps for 1432 models) operation, the modem initiates a
retrain at 4800 bps. If after the first retrain the modem returns on line at 33600 bps (14400 bps for
1432 models, 9600 for 932 models), the modem then starts a counter and a timer. If three retrains
occur within a two minute period, the modem falls back to 4800 bps.
Entering AT#F0 (or AT#F) allows no fallback when on-line.
AT#F1 allows the modem to fallback (based on the error rate or if three retrains have occurred within
a two minute period) from:
2834 Series: 33.6K to 31.2K to 28.8K to 26.4K to 24K to 21.6K to 19.2K to 16.8K to 14.4K to 12K
to 9.6K to 4.8K bps.
1432 Series: 14.4K to 12K to 9.6K to 4.8K bps.
932 Series: 9.6K to 4.8K bps.
The AT#F2 command enables incremental fall back, but also enables incremental fall forward if the
phone line improves. AT#F2 is the factory default setting.
Enable/Disable Lowspeed Fast Connect $FC (2834 Series only)
Entering AT$FC0&W0<CR> sets up the data pump so that it will not transmit a 5 second 2100 Hz
signal. Entering AT$FC0&W0<CR> allows the modem to transmit a 5 second 2100 Hz signal and is
the factory default.
Cleardown at Disconnect &CD (2834 Series only)
The &CD command is used for control of cleardown at disconnect in V.32, V.32bis, V.34 and V.34
enhanced modes.
A cleardown usually adds 1-2 seconds to the time it takes for the modem to go on-hook after a
disconnect. A cleardown makes a disconnect by the remote modem easier to detect and a
subsequent re-connection more likely. Enter AT&CD0&W0<CR> to execute a cleardown at
disconnect (default); and enter AT&CD1&W0<CR> to disable the cleardown function.