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Appendix F 99
Appendix F — Modem AT Command Set
Default values of command parameters, if applicable, are
indicated by an asterisk (*).
Basic AT Commands
A/
Repeat Last Command
Repeats execution of the previous command string. “A/” must not be preceded with AT, or followed by
pressing <Enter>.
A
Answer
Causes the modem to go off-hook and attempt to establish a connection, even in the absence of a ring.
B
n
Line Modulation Options
Configures the modem to the desired communications standard setting at a particular line speed.
B0: Selects CCITT V.22 mode when the modem is at 1200 bps, and CCITT V.21 when the modem is
at 300 bps.
*B1: Selects Bell 212A when the modem is at 1200 bps, and Bell 103 when the modem is at 300 bps.
B2: Selects V.23 originate mode receive 1200 bps, transmit 75 bps; answer mode receive 75 bps,
transmit 1200 bps.
B3: Selects V.23 originate mode receive 75 bps, transmit 1200 bps; answer mode receive 1200 bps,
transmit 75 bps.
Result Codes:
OK Returned when
n
= 0, 1, 2 or 3.
ERROR Returned for any other value of
n
.
C
n
Carrier Control Option (no operation)
This command is included to provide backward compatibility with communications software that issues this
command.
C0: Returns ERROR.
C1: Normal transmit carrier switching.
Result Codes:
OK Returned when
n
= 1.
ERROR Returned for any other value of
n
.