Phone Line Conditioning Commands - Multitech MMH900 User Manual

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.
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.
The AT#F2 command enables
175