V.34 Faxmodem (250-3037) Modem Programming Faxback Doc. # 14479
The AT commands are used to control modem operation and functions.
A command line is a string of characters sent from a PC to the modem while
the modem is in a command state to change the modem behaviors and
functions. A command line has a prefix, a body, and a terminator. Each
command line (with the exception of the A/ command) must begin with the
character sequence AT and must be terminated by a carriage return.
Characters that precede the AT prefix are ignored. Commands entered in
upper case or lower case are accepted, but both the A and T must be of the
same case, i.e., "AT" = ASCII 065, 084 or "at"= ASCII 097, 116. The body
is a string of commands restricted to printable ASCII characters (032-126).
Space characters (ASCII 032) and control characters other than CR (ASCII
013) and BS (ASCII 010) in the command string are ignored. The default
terminator is the ASCII <CR> character.
The modem supports the editing of command lines by recognizing a backspace
character. When modem echo is enabled, the modem responds to receipt of a
backspace or delete by echoing a backspace character, a space character,
and another backspace. The hex value to be used for the backspace
character is programmable through register S5. Values equal to 0 or
greater than 127, or the value which corresponds to the carriage return
character, cannot be used for the backspace character. This editing is not
applicable to the AT header of a command. A command line may be aborted at
any time by entering <cntrl-x> (18h).
The AT sequence may be followed by any number of commands in sequence,
except for commands such as Z, D, or A. Commands following commands Z, D,
or A on the same command line will be ignored. The maximum number of
characters on any command line is 39 (including "A" and "T"). If a syntax
error is found anywhere in a command line command, the remainder of the
line will be ignored and the ERROR result code will be returned.
Most commands entered with parameters out of range will not be accepted and
the ERROR response will be returned lo the PC.
Commands will only be accepted by the modem once the previous command has
been fully executed, which is normally indicated by the return of an
appropriate result code. Execution of commands D and A, either as a result
of a direct command or a re-execute command, will be aborted if another
character is entered before completion of the handshake.
ESCAPE CODE SEQUENCE (+++)
When the modem has established a connection and has entered online data
mode, it is possible to break into the data transmission in order to issue
further commands to the modem in an on-line command mode. This is achieved
by sending lo the modem a sequence of three ASCII characters specified by
register S2. The default character is '+'. The timing of the three
characters must comply with specific time constraints. There is a guard
time before the first character (the pre-sequence lime), a guard time
following the third character (the post-sequence time), and a guard time-
out between the first and second characters and between the second and
third characters (the inter-character time). These times are controlled by
the value recorded in register S12.
BASIC DIALING COMMANDS AND OPTIONS
Dial Command (D)
D is the dial command. You can enter several other associated commands
as part of a dial command. In its simplest form, follow the dial
command with the number you want the modem to dial.
Example: AT D 555-8900 ENTER
NOTE: Your modem ignores the spaces and the dash (-). Your modem
dials the number and waits 30 seconds (default) for a response
from the called modem. If the remote modem answers, your modem
sends the CONNECT, CONNECT 14,400, or CONNECT 9600 result code,
depending on the other modem's speed. Your modem then enters
the communication mode and begins communicating with the remote
modem. If your modem does not hear another modem, it returns a
NO CARRIER or BUSY result code.
Pause (,)
A comma in the dial sequence tells your modem to pause two seconds,
then continue. You might want to use this if you dial from a system
where you have to access an outside line, then dial the outside number.
Example: ATD9, 555-8912 ENTER Dial 9, pause for 2 seconds, then
dial 555-8912.
NOTE: You can use more than one comma to increase the pause time, or
change the time by setting Register S8.
Wait for Dial Tone (W)
A W in the dial sequence tells your modem to wait for a dial tone. You
could use this if you use an alternate long-distance carrier, or if you
dial from a telephone system that requires an access code for a long-
distance number:
Example: ATD23W555-1893 ENTER Dial 23 (long distance code), wait
for a dial tone, dial 555- 1893.
You can use the ATXn command (See AT Command Set) and the contents of
Register S7 determine how long the modem waits for the dial tone. If you
set X2 or X4, your modem wails for 5 seconds. Otherwise, your modem waits
for the time set by Register S7. If your modem does not hear a dial tone
within the specified time, it returns NO DIALTONE.
Wait for Silence (@)
An @ in the dial sequence causes your modem to wait for 5 seconds of
silence after one or more rings. You could use this if you dial a
long-distance service that does not produce a second dial tone. Your
modem waits the length of time specified in Register S7 (default 30
seconds) for the 5 seconds of silence. If the modem does not detect
silence, it returns the NO ANSWER or BUSY result code.
Example: ATDT 555-2323@23 ENTER Dial 555-2323, wait for silence,
dial 23.
Switch hook Flash (!)
An ! causes the modem to perform a flash. This makes the modem hang-up
the phone line for about 0.5 second (like pressing and releasing the
switch hook on your telephone). Some phone systems use this function
to transfer calls.
Example: ATDT555-3439! ENTER Dial 555-3439, flash.
Touch Tone Dialing (T) and Optional Pulse Dialing (P)
The T and P dial modifiers select the dialing method your modem uses.
Your modem defaults to using pulse dialing. You could use this to use
alternate long-distance services from a pulse-dial line.
Example: ATD9WT 555-2322 ENTER Dial 9 pulse mode wait for a dial
tone, dial 555-2322 in tone mode.
Your modem dials using the last method used, so, in the above example,
any additional dial commands use touch tone unless you specify pulse.
Memory Dial Number (S=n)
S=n (where n is 0-3) in the dial sequence makes the modem dial one of
four telephone numbers you previously stored using the Zn command.
Example: ATDS=1 ENTER Dial the number stored in redial memory 1.
Return to Command Mode (;)
A ; in the dial sequence tells your modem to return to the command mode
as soon as it finishes dialing. The modem does not try to detect a
carrier. You would use this command when you use the modem to dial a
voice call.
Example: ATD 555-8373 ENTER Dial 555-8373.
Auto-Dialing Voice Calls
You can have your modem dial any telephone number, even if a computer
is not connected to the other phone. Lift your telephone handset, send
the dialing command, and listen for the other party to answer. At any
time after the dialing stops, you can press any key to disconnect your
modem.
Example: ATDT 555-1281 ENTER Dial 555-1281. When the person
answers, press any key to disconnect the modem.
Dialing Timing Parameters
Registers S6 through S11 control the timing of the dialing commands.
Refer to "Modem S-Registers" for complete information about these
registers.
Auto Answer Operation
You can set your modem to automatically answer calls. This can be a
useful feature if you need to access your computer from another
computer. As set at the factory, the modem does not automatically
answer incoming calls. You control the auto answer feature using
Register S0 which determines the number of rings before your modem
answers. If you set the register to 0 (default) the modem does not
automatically answer the phone. Otherwise, the modem waits for the
number of rings you specify (1-255).
Example: AT S0=1 ENTER The modem answers after one ring.
AT S0=5 ENTER The modem answers after five rings.
AT S0=23 ENTER The modem answers after 23 rings.
After the modem answers, it sends an answer tone and waits for an
originate tone. If the modem hears an originate tone, it returns the
appropriate CONNECT result code to your computer.
If your modem does not detect the carrier within 30 seconds after
answering, it returns a NO CARRIER result code, hangs up, and returns
to the command state.
If your telephone rings when auto answer is disabled, your modem
returns a RING result code and does not answer. You can use the
Immediate Answer command (A) to have your modem pick up the phone line.
Immediate Answer (A)
You can force your modem to pick up the phone line, even if the phone
does not ring. You might use this feature if you called someone on a
voice line, then wanted to switch to communicate with their computer or
if your telephone rings, and you want your modem to answer. If you are
switching from a voice call to a data call, the other party must send
AT D ENTER to their modem.
AT A ENTER The modem immediately picks up the phone line and sends
an answer tone.
Auto Answer Timing Parameters
Registers S0, S7, and S9 control the answer mode timing.
(ALL/tmc-04/08/95)