Multitech MMH900, User Manual

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Appendix J - Internal MMH2834 Composite Link Modem Commands
J.1.6 Phone Line Conditioning Commands
Enable or Disable The MMH2834 has several self-test features (covered in
Recognition Appendix J). The tests are activated with different U commands,
of Remote such as ATU1, and so forth. The &T command is a phone line
Digital Loop Signal conditioning command that enables or disables the modem's
&T
ability to recognize the Remote Digital Loop (RDL) test signal.
The AT&T4 command lets the MMH2834 respond to a RDL
signal, and places itself in digital loop. The AT&T5 command
causes the modem to ignore the RDL signal. The factory default
is &T5.
Enable/Disable This command enables or disables the Trellis Coded Modulation
Trellis Coded of the MMH2834. There is usually no need to disable (turn-off)
Modulation Trellis codings except under an unusual line condition called
#T impulse noise. AT#T0 turns Trellis coding off and AT#T1 turns
Trellis coding on (factory default).
Fallback Modes If line conditions deteriorate, the MMH2834 automatically drops
When On-Line its transmission speed (“fallback”). The #F command control
the different ways the MMN2834 falls back. During operation,
#F if the error rate becomes too great, the modem performs a
retrain. If after the retrain, the error rate is still too high for 28800
bps operation, the modem initiates a retrain at 4800 bps.If after
the first retrain the modem returns on line at 28800 bps, 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 MMH2834 to fallback (based on the error rate
or if three retrains have occurred within a two minute period)
from 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. The AT#F2 command enables
incremental fall back from 28.8K to 4.8K, but also enables
incremental fall forward (from 4.8K to 28.8K) if the phone line
improves. AT#F2 is the factory default setting.