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The AT command set
AT COMMANDS
Table 1-1 summarizes the AT commands. The commands are described in
detail in Tables1-2.
Result codes and messages are listed in Table 1-3.
4.1 COMMAND GUIDELINES
Each AT command has a list of possible parameters with its default
value. The default value is loaded at initialization, i.e., power
turn on or ATZ command. If a command requires a parameter
but no parameter is entered, the modem assumes the parameter is
zero. Invalid commands or parameters return the ERROR message.
The command line may contain a single command or a series of
commands. The commands may be seperated be a space for readability.
The command line may be up to 40 characters in length. The command
line is executed after the terminating character is entered. The
default terminating character is a carriage return (ASCII 013) ,
but this may be changed by writing a different value to register
S3.
The command line may be edited using the backspace character (ASCII
008). This value may be programmed using the S5 register. However,
the backspace will not work for values of 0 and greater than 127,
or for the current value of the terminating character.
All command lines must begin with AT entered in capital or lower
case letters. A command line can be terminated at any time by
isuing CTRL-X (ASCII 018) after entering AT attention code. The
command line will be ignored and an OK result message will be
issued. The A\ command may be used to repeat the last command line.
The A\ does not require a terminating character or the AT
attention code.
The escape code sequence returns the modem to the command mode from
the data mode. A time delay must occur between the last character
transmitted and the first character of the escape code.
The guard time delay can be changed by writing the value to
register S12; (default 1 second). The escape code character must
occur three times in succession for an escape.
Parameters that are entered for the AT and AT& commands are limited
in value to 0-255, where the parameter is "MOD"ed with 256. The
result must be within the specified range; if it is not, the ERROR
message is issued.
Parameters entered for an S register are also "MOD"ed with 256 and
the result is stored in the S register. Parameters that are out of
range are stored in the S register, however, no ERROR message
is reported. Functionally, however, the lower or higher limit is
observed.
Parameters entered for the AT\ and AT% commands follow the same
method, except that if the parameter is out of range, the upper
limit is stored and no ERROR message is reported.
Table 1-1 At Command Summary
COMMAND TITLE DEFAULT
A\ Re-execute Command none
ATA Answer none
ATBn Set CCITT or BELL mode 1(US) *
0(Japan)
ATCn Carrier Control 1
ATDn Dial P
ATE Command Echo 1 *
ATFn On-Line State Character Echo 1 *
ATHn Switch-Hook Control none
ATIn Identification none
ATLn Speaker Volume 2 *
ATMn Speaker Control 1 *
ATNn Modulation Handshake 1 *
ATOn Return To The On-line State none
ATP Set Pulse Dial as Defualt none *
ATQn Result Code Display 0 *
ATSn? Read S Register none
ATSn=x Writing To S Register none
ATT Set Tone Dial as Defualt none *
ATVn Result Code Form (Message Control) 1 *
ATWn Negotiation Progress Reporting 0 *
ATXn Extended Result Codes 4 *
ATYn Control Long Space Disconnect 0 *
ATZn Reset none
AT&Cn DCD Option 0 *
AT&Dn DTR Option 0 *
AT&F Restore Factory Configuration none
AT&Gn Set Guard Tone 0 *
AT&Jn Telephone Jack Connection 0 *
AT&Kn DTE/Modem Flow Control 3 *
AT&Ln Line Type 0 *
AT&Mn Communication Mode (&Qn) *
AT&Pn Dial Pulse Ratio 0(US) 1(Japan)
AT&Qn Communation Mode 5 *
AT&Rn RTS/CTS Option 0 *
AT&Sn DSR Option 0 *
AT&Tn Test and Diagnostoc 4 *
AT&V View Current Configuration and
User Profile none
AT&Wn Store User Profile none
AT&Xn Clock Source Selection 0 *
AT&Yn Designate Default User Profile0
AT&Zn=x Store Phone Number none
AT\An Maximum MNP Block Size 2
AT\Bn Transmit Break 3
AT\E Optimize Echo Cancellation none
AT\Gn Modem to Modem Flow Control 0
AT\Kn Break Control 5
AT\Ln MNP Block Transfer Control 0
AT\Nn Operation Mode Control 3
AT\O Originate Reliable Link Control 0
AT\Tn Inactivity Timer Control 0 *
AT\U Accept Reliable Mode Control none
AT\Y Switch to Reliable Mode none
AT\Z Switch to Normal Mode none
AT%Cn Compression Control 1 *
AT%Dn Set Dictionary Size (V.42 bis)2
AT%En Enable/Disable Auto Retrain 0
AT%L Report Receive Signal Level none
AT%Mn Set One/Two-Way Mode (V.42 bis3
AT%P Clear V.42 bis Encoder Dictionary none
AT%Q Report Line Signal Quality none
AT%Sn Set Maximum String Length (V.42 bis) 32
* Command setting may be stored in one of two user profiles with
the AT&Wn command.
Table 4-2 At Command Definitions
A\ Re-execute Command. Re-executes the most recent AT command
string. The principle application of this command is to place
another call (e.g., Dial command) that failed to connect due to
busy line, no answer, or a wrong number. This command must appear
alone on a command line and must be terminated by the "/"
character. (A <CR> should not be entered to terminate the command)
Parameters : None
Default : None
ATA Answer. This must be the last command entered into the command
line. The modem proceeds with the connect sequence in answer mode.
The modem will enter the connect state after exchanging carrier
with the remote modem. If no carrier is detected within the wait
period specified in register S7 (default=50 seconds), the modem
will disconnect. Any character may be entered via the DTE during
the connect sequence to abort the command.
Parameters : None
Default : None
Result codes :
CONNECT XXXX If a connected is established (XXXX =
telco line speed, e.g., 2400)
NO CARRIER If a connection cannot be established, the
abort timer (register S7) expires, or if the
command is aborted.
ERROR If in data mode.
ATBn Set CCITT or BELL Mode. Selects between CCITT or BELL modes
for 1200 and 300 bps. This command is not valid
when the ATN1 command (automode detection enabled)
is in effect.
Parameters : 0, 1
Default : 1 for U.S., 0 for Japan
Result codes :
OK for all valid parameters.
ERROR otherwise
Command options:
ATB0= Selects CCITT V.22 and V.21 standards for
communications at 1200 and 300 bps.
ATB1= Selects Bell 212A and 103 standards for
communications at 1200 and 300 bps.
ATCn Carrier Control. Controls the transmit carrier. The modem is
preset to turn carrier on and off as necessary (the C1 option). The
signal is on when the modem is calling, answering, or connected to
the remote modem, and is off when it is not. The C0 option is NOT
valid.
Parameters : 0, 1
Default : 1
Result codes :
OK for 1.
ERROR otherwise.
Command options:
ATC0 Not permitted, return error result code.
ATC1 Normal transmit carrier switching (preset).
ATDn Dial. This must be the last command on the command line. ATD
causes the modem to go off-hook, dial according to the parameters
entered, and attempt to establish a connection.
If there are not parameters, then the modem goes off-hool in
originate mode without dialing a number. Punctuation may be used
for clarity. Parentheses, hyphens and spaces are ignored. If any
invalid character is entered, that character and all subsequent
characters in the dial string are ignored. The modem truncates dial
strings to 40 character.
Parameters :0-9 A B C D * # L P T R ! @ W , ; ^ S=n
Default : P
Result codes:
OK If ";" dial modifier is used.
OK If key press abort during dialing process.
NO DIALTONE If ATX2 or ATX4 is selected and 1 second
of dial tone is not detected within 5 seconds;
or if W dial modifier is used and 3 seconds of
dial tone is not detected within the time specified
by S7.
BUSY If busy is detected, and ATX3 or ATX4 is
selected or if W dial modifier is used.
NO ANSWER If "@" dial modifier is used and 5 seconds of
silence is not detected within the time specified in S7.
CONNECT XXX If a connection is established.
NO CARRIER If a connection cannot be established, the
abort timer (register S7) expires, or a character is
entered during the handshake process.
ERROR If in data mode.
The ATD Parameters are :
L Dials the last dial string that was dialed.
P Use Pulse Dialing. Placed at the end of the command
string and before the dial string. Causes the modem to pulse
dial the numbers.
T Uses the DTMF dialing. Placed at the end of command
string and before the dialing string. Causes the modem to use
DTMF tones to dial.
R Reverse mode. Allows the modem to call an
originate-only modem by forcing the call into
"answer mode". Must be entered as the last character
of the command string (just before the <CR>).
! Hookflash. Causes the modem to go on-hook for 700
millisecinds and then off-hook.
@ Causes the modem to listen for 5 seconds of silence.
If a 5 second of silence. If a 5 second silence has not been
detected within the period specified in S7 (default = 50 seconds),
the modem disconnects and returns the 'NO ANSWER' result code.
If it detects a busy signal, it returns a 'BUSY' result code. If the
5 seconds of silence is detected, then the modem continues dialing
the dial string.
W Wait for Dial Tine Before Dialing. Causes the modem
to wait for a dial tone up to the period of time specified in S7
(default = 50) before dialing the number that follows. If the modem
detects a dial tone before the given time delay, it continues to
dial. Otherwise, it goes on-hook.
, Pause During Dial. Inserted between digits in a dial
string. Causes the modem to pause for the value given by register
S8 (default = 2 seconds), before dialing the next digit. This delay
can be used in place of the "Wait For Dial Tone Before Dialing".
; Return To Command Mode After Dialing. Added to the end of the dial
string. Causes the modem to remain in the command mode after it
dials the digits preceding the command. This allows the user to
issue additional dial commands or dial string without overflowing the command buffer.odem looks for the carrier
after the final dial command is issued. "ATHn" aborts this command.
^ Turn On Calling Tone. Turns on the periodic 1300 Hz
calling tone if originating the call. Calling tone is enabled only
on call-by-call basis.
S=n Dial Stored Number. Follows the dial command string.
Causes the modem to dial a telephone number previously stored in
directory location n using AT&Zn command.If "ATD" is entered
without parameters, the modem goes off-hook and waits for carrier;
if the handshake is not completed wihtin the period of time specified
in register S7 (default = 50 seconds) the modem goes on-hook.
The ATD command will be aborted in progress upon receipt of any
character from DTE before completion of the handshake.
ATE Command Echo. Controls the echo of characters received by the
modem from the local DTE while the modem is in command mode.
Paramaters : 0, 1
Default : 1
Result codes :
OK for 0 and 1.
ERROR otherwise.
Command options:
ATE0= Inhibits the echoing of commands.
ATE1= Enales the echoing of commands.
ATFn On-Line State Character Echo. Determines if the modem will
echo data from the DTE. The modem does not support the ATF0
command. However, the modem will accept ATF1 which may be issued by
some communication software packages.
Parameters : n = 0, 1
Default : 1
Result codes:
OK for 1
ERROR otherwise
Command options:
ATF0= ERROR
ATF1= Disables on-line echo
ATHn Switch-Hook Control. Applies to asynchronous operation only.
If the user enters the command mode from the data mode by issuing
the escape sequence (+++), or as a result of an ON-to-OFF
transition of DTR of the AT&d1 option in effect, the user may cause
the modem to go on-hook (disconnect) by issuing the ATH command.
Parameters : n=0, 1
Default : none
Result codes:
OK for 0 and 1
ERROR otherwise
Command options:
ATH0= Causes the modem to go on-hook (hang up).
ATH1= If modem is on-hook, modem goes off-hook,
returns an OK response, and awaits further commands.
ATIn Identification. Return the product code, returns the checksum
of firmware ROM, or computes the checksum of the firmware ROM and
reports its error status.
The product code contain 3 digits. The checksum result
consists of three ASCII numeric characters followed by a carriage
return and a line feed. The error status is either OK or ERROR.
Parameters : n = 0-2
Result codes :
OK
Default : none
Command options:
ATI0 : Reports the product code.
ATI1 : Reports the checksum computed on the firmware ROM.
ATI2 : Performs a checksum on the firmware ROM and
indicates OK or ERROR.
ATI3 : Reports firmware revision level.
ATI4 : Reports product capabilities.
ATLn Speaker Volume. Controls the internal speaker volume.
Parameters : 0-3
Default : 2
Result codes :
OK for 0 to 3.
ERROR otherwise.
Command options:
ATL0 : Selects low speaker volume.
ATL1 : Selects low speaker volume.
ATL2 : Selects medium speaker volume.
ATL3 : Selects high speaker volume.
ATMn Speaker Control. Controls the internal speaker while the modem
is receiving a carrier signal or dialing. This command also enables
or disables the speaker.
Parameters : n = 0 to 3
Default : 1
Result codes :
OK for 0 to 3.
ERROR otherwise.
Command options:
ATM0 Speaker is always off.
ATM1 Speaker is on during handshaking in call
establishment but is turned off while the modem is
receiving a carrier signal from the remote modem.
ATM2 Speaker is always on.
ATM3 Speaker goes off while the modem is receiving a
carrier signal from a remote modem and while the
modem is dialing. However, speaker is on
during answering.
ATNn Modulation Handshake. This command can be used to assure that
a connection is made only at the specified speed. If leased line is
selected, this command is ignored and the modem operates as if ATN0
were selected.
Parameters : 0, 1
Default : 1
Result codes :
OK for 0 and 1.
ERROR otherwise
Command options:
ATN0= Requires that the speed of the connection be
that specified by the calue held in S37; if S37=0, the speed of the
connection must match that at which the last AT command was issued.
If the selected speed can be achieved using more than one
communication standard (e.g., Bell 212A or CCITT V.22 at 1200
bps), the modem also references the selection made with the
ATB command.
ATN1= Permits handshaking to occur at any speed
supported by both modems. Enables automode detection. The ATB
command is ignored in this mode and the modem attemps only CCITT
mode connections.
ATOn Return To The On-Line Status. Applies to asynchronous
operation only. If the user enters the command mode from the data
mode by issuing the escape sequence, or as a result of an
ON-to-OFF transition of DTR with the AT&d1 option in effect, the
user may return to data mode without terminating a call by issuing
the ATO command.
This command may also be used to force a retrain.
If the modem is on-hook, then the modem behaves as if it went
off-hook to originate without actually taking the relay off-hook.
Parameters : 0, 1
Default : none
Result codes:
ERROR If &T1, &T3, or &T6-&T8 is active.
CONNECT XXX If a connection is established.
NO CARRIER If retrain is not successful in the time
specified by S7.
Command options:
ATO0= Causes the modem to turn to the data mode.
ATO1= Causes the modem to return to the data mode and
to initiate a retrain when operating at 2400,
4800, 9600, 12000, 12400 bps.
ATP Set Pulse Dial as Default. Causes the modem to assume that all
subsequent dial commands are pulse dialed. The user may omit the
"P" from the dial string.
Parameters : none
Default : none
Result codes :
OK If issued outside dial string.
ATQn REsult Code Display. Determines whether or not the modem sends
the result codes to DTE. (See ATXn command.)
Parameters : n = 0, 1, 2
Default : 0
Result codes :
OK for 0 and 2.
none for 1.
ERROR otherwise.
Command options:
ATQ0= Allows the modem to send the result codes to
the DTE.
ATQ1= Prohibits the modem from sending result codes
to the DTE.
ATQ2= Modem return result codes to DTE when
originating a call; does not return
result codes when answering a call with the
exception of OK and ERROR.
ATSn? Reading S Register. Reads the contents of the S register.
All the S registers may be read.
Parameters : n = 0-95
Default : none
Result codes :
OK for all parameters.
ATSn=x Writing to S Registers. Writes the value of x to the
specified S register. All the registers will return the OK response
if x is a legal value, however, some registers will not actually
write the value anywhere. These registers are S1, S13-S15, S17,
S20-S24, and S27.
Parameters : n = 0-95, x = 0-255
Default : none
Result codes :
OK for parameters n=0-95.
OK for no argument.
ERROR otherwise.
ATT Set Tone Dial as Default. Causes the modem to assume that all
aubsequent dial commands are tone dialed. The user may omit the "T"
from the dial string.
Parameter : none
Default : none
Result codes :
OK if issued outside dial string.
ATVn Result Code Form (Message Control). Selects whether the modem
sends long form or short form result codes to the DTE. All
responses are ASCII values. Long-form (verbose) responses are
preceded and terminated with both carriage return and line feed
control characters. Short-form (numeric) responses are only
terminated with a carriage return control character. (See ATXn
command).
Parameters : 0, 1
Default : 1
Result codes :
0 for 0.
OK for 1.
ERROR otherwise.
Command options:
ATV0= Allows short-form (numeric) result codes to be
sent.
ATV1= Allows long-form (verbose) result codes to be
sent.
ATWn Negotiation Progress Reporting. An additional set of result
codes can be enabled with the W command to report progress of the
negotiation phase of error-correction mode. These codes report the
carrier speed (300 bps-2400 bps) and the error-correction protocol.
These messages can also be reported in either numeric or verbose
form. For example, both 77 and PROTOCOL:LAP-M indicate that the
error-correction protocol is LAP-M (See ATXn command.)
If the error-correction link is negotiated and the connection
is made, the appropriate CONNECT XXXX message is reported.
When in error-correction mode, the CARRIER XXXX message may
indicate one speed, while the CONNECT XXXX message reports another.
Parameters : 0-2
Default : 0
Result codes:
OK for parameters 0-2.
ERROR otherwise.
Command options:
ATW0 Error-correction call progress not reported.
ATW1 Error-correction call progress reported.
ATW2 Error-correction call progress not reported. CONNECT
XXXX message reports DCE speed.
ATXn Extended Result Codes. Determines whether the modem responds
to dial tone and busy signals, and how it displays result codes for
CONNECT messages. When the modem ignores dial tone, it waits for a
time delay given by register S6 (default = 2 seconds) and then
dials regardless of presence or absence of dial tone; this is
called blind dialing.
Parameters : 0-4
Default : 4
Result codes:
OK for parameters 0-4.
ERROR otherwise.
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