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Appendix F - MMH2834 Modem Commands
Enable/Disable Auto-Reliable Fallback Character $F
In Auto-Reliable mode, the modem is given four seconds to establish a Reliable connection. If a
single CARRIAGE RETURN is received from the remote modem during this four second period,
the Auto-Reliable modem assumes that the remote modem is not in Reliable mode and drops to
Normal mode. The CARRIAGE RETURN is the only character which causes the modem to drop
to Normal mode. Any other character will either be buffered or discarded.
The $F command can be used to disable this fallback-to-Normal-due-to-CARRIAGE-RETURN
feature.
The Auto-Reliable fallback character ($F) and Auto Reliable buffering ($A) commands can be
used together to cause the modem to buffer all data received up until the CARRIAGE RETURN,
and then drop to Normal mode. All data received will then be output following the CONNECT
message.
AT$F0 = Do not fall back to Normal if CARRIAGE RETURN received.
AT$F1 = Fall back to Normal mode if CARRIAGE RETURN received.
The factory default is $F0.
Retransmit Count $R
Retransmit Count If errors are received during a Reliable connection, the modem re-sends the
block of data which contained an error. With the $R0 command, if another error occurs, the block
will be re-sent again. The modem counts the number of times that a data block is re-sent. If the
same block of data is resent 12 times and still has not been received properly, the modem
assumes that the transmission line is unsuitable for transmission, and abort the connection.
This retransmit counter is disabled by the $R1 command. When the retransmit counter is
disabled, the modem keeps trying to send data and will not abort, no matter how many times the
same block is resent.
AT$R0 = Disconnect if retransmit count is exceeded.
AT$R1 = Do not disconnect due to retransmits.
The factory default setting is $R0.
V.42 Error Correction/300bps $E
At 300 bps, error correction is not typically used. $E1 lets the MMH2834 function at 300 bps in
either Normal (&E0), Auto-Reliable (&E1) or Reliable (&E2) mode. $E0, which is the the
MMH2834’s default, disables 300 bps/V.42 error correction altogether.