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SERIES II INTELLIGENT DATA/FAX MODEMS
Auto Speed Detect #A
The function of the #A command is to detect and select the operational
data rates (the “starting” speeds) with which the Series II Modem uses
for initial handshake and speed selection.
Remember, this command does not control the originating data rate of
the modem (that is done by the Modem Baud Rate command $MBn),
but only the Answer mode “starting” speeds. Entering
AT#A0 (or AT#A) causes the Modem to operate starting at 33,600 bps,
with fallback to 28,800 to 19,200 to 14,400 to 9600 to 4800 to 2400 to
1200 and to 300 bps. Entering AT#A1 causes 33,600 bps operation only.
Entering AT#A2 causes the modem to operate at starting speeds of
33,600 bps, with incremental fallback to 28,800, 19,200, 14,400, 9600
and 4800 bps. The AT#A3 command causes the modem to begin
operation as a V.22bis modem at 2400 bps, with fallback to 1200
to 300 bps. AT#A0 is the factory default value.
5.4.7 RS232C Interface Control Commands
Carrier Detect Control &C
The &C command allows you to control the status of the Carrier Detect
signal (CD, Pin 8) on the RS232C line. You have four choices.
You can force the signal high, or allow it to act normally, or force the
modem to reset when CD drops, or set it to stay high until the modem
disconnects, go low momentarily, and then go high again. The last
option is useful with some CBX phone systems and mainframe front
ends, which require CD to act in this manner.
To allow CD to act normally, enter the command AT&C1 (the factory
default setting). To force CD on, enter AT&C0. To reset the modem to
its current parameters when CD drops, enter AT&C4. To set up CD so
that it drops for one second on disconnect and then comes up again,
enter AT&C2. (If you want the drop time to be something other than
one second, use S-Register S24 to change this value. Refer to the
Chapter 6 instructions for S24.)