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Chapter 5 - Error Correction, Data Compression, and Speed Conversion
5.13 Related Commands
5.13.1 Autoreliable Buffering ($A)
In autoreliable mode, the modem is given four seconds to establish a reliable connection. If it cannot
establish a reliable connection in that time, the modem drops to non-error correction mode. Any data
received during this period is normally discarded. The $A command is used to cause the modem to buffer
(save) data that is received during the autoreliable time-out period. This data is then output by the modem
after it sends the CONNECT message.
Type AT$A0 to discard data received during the autoreliable time period (factory default).
Type AT$A1 to buffer data received during the autoreliable time period.
5.13.2 Maximum Block Size (&BS)
The maximum size of reliable mode data blocks is controlled by the &BS command. MNP Class 3 sends
blocks of 1 to 64 characters. MNP Classes 4 and 5 normally send blocks of 1 to 256 characters. Reducing the
block size for Classes 4 and 5 to 64 characters may give a smoother flow of data, and improve throughput
performance on noisy phone lines. Using smaller block sizes over good phone lines may cause a slight loss
in data throughput.
Type AT&BS0 for a maximum transmit block size of 64 characters.
Type AT&BS1 for a maximum transmit block size of 256 characters (factory default).
5.13.3 Autoreliable Fallback Character ($F)
In autoreliable mode, the modem is given four seconds to establish a reliable connection. If a single carriage
return character, <CR>, is received from the remote modem during this four second period, the autoreliable
modem assumes that the remote modem is not in reliable mode and drops to a non-error correction mode.
The carriage return character is then output following the CONNECT message. The carriage return character
is the only character that causes the modem to drop to non-error correction mode. Any other data is either
buffered or discarded.
Use the $F command to disable this fallback feature. The autoreliable fallback character ($F) and the auto
reliable buffering ($A) commands can be used together to cause the modem to buffer all data received up to
the carriage return and then drop to non-error correction mode. All data received will then be output following
the CONNECT message.
Type AT$F0 to cause the modem not to fall back to non-error correction mode if a carriage return character is
received.
Type AT$F1 to cause the modem to fall back to error correction mode if a carriage return character is
received (factory default).