1-19
APPENDIX C: AT COMMAND
Modem AT Commands
Basic AT Command Set
Command
Options
Function & Description
A/
Re-execute the last command string
<any key>
Terminate the current connection attempt
when entered in handshaking state
All the following commands require an “AT” prefix
A
Go off-hook and attempt to establish a
connection without waiting for a ring
Bn
Line modulation options
B0
Select V.22 mode for 1200 bps connection
B1 *
Select Bell 212A for 1200 bps connection
B2
Select V.23 1200 bps for receiving, 75 bps
for transmitting in originate mode; 75 bps
for receiving and 1200 bps for transmitting
in answer mode
B3
Select V.23 75 bps for receiving, 1200 bps
for transmitting in originate mode; 1200 bps
for receiving and 75 bps for transmitting in
answer mode
B15
Select V.21 for 300 bps connection
B16
Select Bell 103 for 300 bps connection
Dn
Dial command, beginning the dialing
sequence. The string “n” (telephone number
and modifiers) listed as follows is entered
after the “D” command
L
Re-dial last number. Should be the first
character following ATD, ignored
otherwise
P
Pulse dial.
R
Reverse dial. Originate call in answer
mode (go on-line in answer mode)
S=n
Dial the phone number stored in NVRAM
at location “n” (n=0, 1, 2, 3)
T
DTMF tone dial.
W
Wait for second dial tone. The modem
waits for the second dial tone before
processing the dial string
,
Pause. Cause the modem to pause for a time
before processing the next character in the
dial string (specified by S8 register)
