Hayes AT command set
Hayes AT Commands
AT or at always precedes a command. The modem needs these two letters to adjust itself to the settings of the PCs comport. The modem then switches automatically to the defined baud rate and parity, until the next command is issued or the modem is turned off. The modem will not respond to any commands not preceded by an AT.
The modem recognises following formats :
1 or 0 start bits, 7 or 8 data bits, no, odd or even parity and 1 or 2 stop bits.
The commands can be issued at a rate between 300 and 115,000bps. In V.23 mode, the commands are sent at 1,200bps. The modems replies are then sent at 75bps to the PC.
The command interpreter recognizes AT and at, but not At or aT. Both characters have to be sent in upper- or lowercase and must be sent directly after one another.
A/ Repeat last command, no <CR>
ATA Answer incoming call
When you want to answer a call manually, you type this command after a ring has appeared on the screen of your Terminal emulator.
D Dial a telephone number
ATDTn After issuing this command, the modem will attempt to establish a connection and dial the number n.
Options to the command D:
@ Wait for silence for 5 seconds.
, Pause for 2 seconds (S8)
! Flash ( on-hook for value in S29 )
; Return to command mode after dialing.
P Pulse dial
T Tone dial
n The telephone number to be dialed
Sn Dial number stored in directory entry &Zn where n=0..19. The selected number is shown on the screen for verification.
J Perform MNP10 link negotiation at highest supported speed (for this call only).
L Redial last number.
^ Disable calling tone, this call only.
The call can be aborted at any stage before the connect message appears, by entering any character except Linefeed.
ATE Command echo to host
E0 Commands are not echoed
E1 Commands are echoed
With this command you can select if the modem should return all the commands to the screen or not. This is useful to check if all characters are received by the modem. If characters appear double on the screen, disable echoing by the modem or by your terminal. The value of ATE can be written in the RAM of the modem using AT&W.
ATFn Select transmission mode/speed
F0 Auto mode
F1 V.21 300bps
F3 V.23 75Tx/1200Rx with AT%F1
V.23 1200Tx/75Rx with AT%F2
F4 V.22 1,200bps
F5 V.22bis 2,400bps
F6 V.32bis 4,800bps
F7 V.32bis 7,200bps
F8 V.32bis 9,600bps
F9 V.32bis 12,000bps
F10 V.32bis 14,400bps
These commands are not valid for V.34 modems. The equivalent command for the V.34 modems is +MS, please refer to this command.
ATH Go on-hook, hang up.
H0 Go on-hook ( Hang up )
H1 Go off-hook
I0 Product code
I1 Pre-computed Checksum
I2 Returns OK
I3 Returns OK
I4 OEM String
I5 - I11 Returns OK
I12 ROM Checksum
I13 RC Version number
I14 Shows Firmware version
I15 Shows selected country
I17 GSM option
I18 Shows Supported GSM Kit (GSM-ready only)
ATL Speaker volume settings
L0 Lowest speaker volume
L1 Low speaker volume
L2 Medium speaker volume
L3 Highest speaker volume
With this command the speaker volume can be set.
ATM Speaker control
M0 Speaker always off
M1 Speaker on until carrier detected
M2 Speaker always on
M3 Speaker on only while answering
ATNn Select Auto mode
N0 Auto mode disabled
N1 Auto mode enabled
This command is not longer valid for the V.34 modems.
ATOn Return to data mode
O0 Return to data mode from command mode, only if on-line.
O1 Return on-line and initiate retrain (2400bps or higher)
ATQn Result codes
Q0 Modem returns result codes
Q1 Quiet mode enabled. Modem gives no result codes.
If the quiet mode is enabled, the responses from the modem are not sent to the PC.
ATSn Sets and reads the selected register
Sn=x Sets register n to the value x
Sn? Reads the value of register n
n is a numeric value, varying between 0 and 255 (depending on the register).
ATVn Result codes in numerical or verbose form
V0 Returns the code in numerical form
V1 Full-word result codes
ATWn Connect messages formatting
W0 DTE rate ( connect rate )
W1 Hayes 4 line format : Carrier, Protocol, Compression, DTE rate
W2 Result code is DCE rate ( carrier rate )
ATXn Extended Result codes
X1 Ignore dialtone and busy tone
X2 Ignore busy tone
X3 Inner dialtone
X4 Modem recognises dialtone and busy tone
X3 and X1 set the modem for Blind Dialing. This option is country specific, because some countries do not allow blind dialing.
ATYn Long Space disconnect
Y0 Disable long space disconnect
Y1 Enable long space disconnect
If the modems receives after activating this function, a BREAK-signal of at least 1.6 seconds coming from the remote PC, it will send a BREAK-signal of 4 seconds back to the remote PC before hanging up the telephone line.
ATZn Resetting the modem
Z0 Restore stored profile 0
Z1 Restore stored profile 1
If this command is issued to the modem during a connection, the modem will drop the line. According to the parameter n, the modem will restore the values stored in the non-volatile RAM (See also &W ).
&C0 DCD is always active
&C1 DCD is active if modem is on-line
Data Carrier Detect (DCD) is a hardware signal that notifies the software that the modem is in communication with another modem. Most softwares will not start-up properly if the DCD is active. Default is &C1.
AT&Dn Data Terminal Ready settings
&D0 Modem ignores DTR
&D1 Go to command mode on ON-to-OFF DTR transition.
&D2 Hang up on DTR-drop and go to command mode
&D3 Reset (ATZ) on DTR-drop. Modem hangs up.
AT&F Restore Factory Settings
&F0 Use profile 0
&F1 Use profile 1
The modem is reset to the default firmware settings. If the modem is on-line, the command will not be executed.
AT&Gn Select guard tone
&G0 Disables guard tone
&G1 Disables guard tone
&G2 Selects 1800Hz guard tone
This command may not be permitted in some countries.
AT&Kn Flow Control
&K0 Flow control disabled
&K3 RTS/CTS flow control (Hardware)
&K4 XON/XOFF flow control (Software)
&K5 Transparent XON/XOFF flow control
&K6 RTS/CTS and XON/XOFF flow control
Flow control is the use of characters or RS232 signals to start and stop the flow of data to avoid data loss during buffering. This is extremely important when the DTE/DCE rate is different from the line speed, e.g. when data compression is used. The DTE/DCE rate must be higher then the line speed.
RTS/CTS flow control (Hardware flow control)
The PC will send data to the modem. The modem will store this data in a buffer. When this buffer is full, the modem will drop the CTS-line, telling the PC that it has to stop transmitting data until the signal raises again. If the RTS-signal is OFF, transmitting data to the PC is stopped until the signal switches to ON.
XON/XOFF flow control (Software flow control)
If the modem receives a XON-character (S32) from the PC, it stops transmitting data to the PC until it receives a XOFF-character (S33). The process is similar if the PC is sending data to the modem.
NOTE : The preferable setting is RTS/CTS flow control
AT&Pn Pulse dial make-break
&P0 : 61/39 ratio at 10pps
&P1 : 67/33 ratio at 10pps
&P2 : 39/61 ratio at 20pps
&P3 : 33/67 ratio at 20pps
Settings may be locked depending on country selection. Default is also country dependent.
AT&Qn Sync/Async Mode
&Q0 : Selects direct async operation.
&Q1 : Selects synchronous connect mode with async off-line command mode.
&Q2 : Selects synchronous connect mode with async off-line command mode and enables DTR dialing.
&Q4 : Selects Autosync mode
&Q5 : The modem will try to negotiate an error corrected link.
&Q6 : Selects async operation in normal mode.
This command is used to control the connection modes permitted.
AT&Rn CTS/RTS option
&R0 : In sync mode, CTS tracks the state of RTS. In async mode, CTS acts according V.25bis handshake.
&R1 : In sync mode CTS is always on. In async mode, CTS will drop only if required by flow control.
This selects how the modem controls CTS. CTS operation is modified if hardware FC is selected ( AT&Kn ).
AT&Sn DSR Override
&S0 : DSR will remain on at all times.
&S1 : DSR will become active after answer tone has been detected and inactive after the carrier has been lost.
This command selects how the modem will control DSR.
AT&Tn Test and diagnostics
&T0 : Terminates test
&T1 : Initiates local analogue loop back
&T2 : Returns ERROR
&T3 : Initiates local digital loop back
&T4 : Enables digital loop back acknowledgment for remote request.
&T5 : Disables digital loop back acknowledgment for remote request.
&T6 : Requests a remote digital loop back without self test.
&T7 : Requests a remote digital loop back with self test
&T8 : Initiates local analogue loop back with self test.
The modem will perform selected test and diagnostic functions according to the parameter supplied. A test can be run only when in an asynchronous operation in non-error-correction mode. To terminate a test in progress, the escape sequence must be entered first, except for parameters 7 and 8.
AT&Vn Display current configuration and stored profiles
Reports the current (active) configuration, the stored (user) profiles, and the first four stored telephone numbers.
AT&Wn Store current configuration
&W0 : Store current configuration in profile 0
&W1 : Store current configuration in profile 1
AT&Xn Select Synchronous Clock Source
&X0 : Selects internal timing
&X1 : Selects external timing
&X2 : Selects slave receive timing
Selects the source of the transmit clock for the synchronous mode of operation.
AT&Yn Designate a default reset profile
&Y0 : The modem will use profile 0
&Y1 : The modem will use profile 1
Selects which user profile will be used after a hard reset.
AT&Zn Store telephone number
&Zn=x n=0 to 3 and x=dial string
AT%En LQM and Auto-retrain or FB/FF
%E0 : Disable Line Quality Monitor and auto-retrain
%E1 : Enable Line Quality Monitor and auto-retrain
%E2 : Enable Line Quality Monitor and fall back/fall forward. (V.34 only)
Controls whether or not the modem will automatically monitor the line quality and request a retrain or fall back / fall forward depending on the line quality.
AT%Cn Enable/Disable data compression
%C0 : Disables data compression
%C1 : Enables MNP5
%C2 : Enables V.42bis
%C3 : Enables both V.42bis and MNP5 data compression.
Enables or disables data compression negotiation. The modem can only perform data compression on an error corrected link.
AT\Gn Modem to modem flow control
\G0 : Disables modem-to-modem flow control
\G1 : Enables modem-to-modem flow control
In non-error correction mode, the modem enables or disables the generation or recognition of modem to modem XON/XOFF flow control according to the parameter supplied. In error correction mode, the setting of \G is ignored.
AT\Nn Operating mode
\N0 : Normal speed buffered mode. (&Q6)
\N1 : Serial interface selected. (&Q0)
\N2 : Reliable connection ( First V.42 the MNP4). Failure to make a reliable connection results in modem hanging up.
\N3 : Auto reliable mode ( First V.42, then MNP4 then speed buffered )
\N4 : V.42 (LAPM) . If connection fails, modem hangs up.
\N5 : MNP4 EC mode. Failure results in hanging up.
This command controls the preferred error correcting mode to be negotiated in a subsequent data connection.
\An Select maximum MNP block size
\A0 64 characters
\A1 128 characters
\A2 192 characters
\A3 256 characters
)Mn Enable cellular power level adjustment
)M0 : Disables transmit power level adjustment during MNP10 link negotiation.
)M1 : Enables transmit power level adjustment during MNP10 link negotiation. V.34 : Uses the @Mn value to establish initial cellular connection. After connection power level is determined by modem.
)M2 : Enables transmit power level adjustment during MNP10 link negotiation. Uses the @Mn value to establish initial cellular connection. After connection power level is fixed. (V.34 only)
Enables or disables automatic adjustment of the transmit power level to accommodate the signaling requirements of cellular telephone equipment.
-Kn MNP Extended Services
-K0 Disables V.42 LAPM to MNP10 conversion
-K1 Enables V.42 LAPM to MNP10 conversion
-K2 Enables V.42 LAPM to MNP10 conversion, inhibits MNP ES initiation during V.42 LAPM answering mode detection Phase (V.34 only)
Enables or disables conversion of a V.42 connection to a MNP10 connection.
Following commands are valid only for the V.34 modems.
@Mn Initial Cellular Power Level setting
@M0 -26dBm (Default)
Sets the initial power level for up shift at connect until line conditions can be determined.
:En Compromise Equalizer Enable command
:E0 Disables the equalizer
:E1 Enables the equalizer
Enables or disables the V.32 compromise equalizer. This command can be used when the modem is attached to either a flat line or a cellular connection.
+MS Select Modulation
Note : The use of the Nn command is not recommended for speeds higher than 14.400.
+MS? Reports selected options
response : +MS:11,1,300,33600 (example)
+MS=? Reports supported options
response : +MS:(0,1,2,3,8,9,10,13,64,69,74),(0,1),(300-33600),(300-33600)
Sub parameter definitions:
|V.22bis||2400 or 1200|
|V.34||33600,32100,28800, 26400,24000, 21600, 19200, 16800, 14400,9600,7200, 4800, 2400|
|V.FC||28800,26400,24000,21600, 19200, 16800, 14400,9600,7200,4800,2400|
2. <Auto mode> is an optional numeric value which enables or disables automatic modulation negotiation using V.8 or V.32bis Annex A. The options are :
0 Auto mode disabled
1 Auto mode enabled using V.8 or V.32bis Annex A
The default value is 1, which enables auto mode. Note, however, there are modulations for which there is no automatic negotiation, e.g., Bell 212.
The modem connects at the highest possible rate in accordance with V.8 or V.32bis Annex A if V.8 is not supported by the remote modem.
A. If <max_rate> is greater than the highest speed supported by then modulation specified by <mod>, the modem auto modes down from the highest rate to the selected modulation. For example : +MS=10,1,1200,24000 selects auto moding down from V.32bis 14400bps.
B. To emulate issuance of the N1 command, specify the modulation and the rate to start auto moding down from using <mod> and <max_rate>, respectively. Examples :
+MS=11,1,300,16800 auto mode at V.34 16800bps
+MS=9,1,300,12000 auto mode at V.32bis 12000bps
3. <Min_rate> is an optional number which specifies the lowest rate at which the modem may establish a connection. The value is decimal coded, in units of BPS, e.g. 2400 specifies the lowest rate to be 2400. The default is 300 for 300bps.
3. <Max_rate> is an optional number which specifies the highest rate at which the modem may establish a connection. The value is decimal coded, in units of BPS, e.g. 14400 specifies the lowest rate to be 14400. The default is 33,600 for 33,600bps.
AT Command Result Codes
The modem responds to commands from the DTE ( PC ) and to activity on the line by signaling to the DTE in the form of result codes. The result codes that the modem can send are described below.
3 NO CARRIER
5 CONNECT 1200
6 NO DIALTONE
8 NO ANSWER
9 CONNECT 0600
10 CONNECT 2400
11 CONNECT 4800
12 CONNECT 9600
13 CONNECT 7200
14 CONNECT 12000
15 CONNECT 14400
16 CONNECT 19200
17 CONNECT 38400
18 CONNECT 57600
19 CONNECT 115200
22 CONNECT 75TX/1200RX
23 CONNECT 1200TX/75RX
40 CARRIER 300
44 CARRIER 1200/75
45 CARRIER 75/1200
46 CARRIER 1200
47 CARRIER 2400
48 CARRIER 4800
49 CARRIER 7200
50 CARRIER 9600
51 CARRIER 12000
52 CARRIER 14400
53 CARRIER 16800
54 CARRIER 19200
55 CARRIER 21600
56 CARRIER 24000
57 CARRIER 26400
58 CARRIER 28800
59 CARRIER 31200
60 CARRIER 33600
61 CONNECT 16800
62 CONNECT 21600
63 CONNECT 24000
64 CONNECT 26400
65 CONNECT 28800
66 CONNECT 33600
67 COMPRESSION: CLASS 5
68 COMPRESSION: V.42 bis
69 COMPRESSION: NONE
70 PROTOCOL: NONE
77 PROTOCOL: LAPM
80 PROTOCOL: ALT
81 PROTOCOL: ALT-CELLULAR
To change the country settings, use followingfollow next procedure :
Modem responds with OK
Modem responds with OK
Note : Some counties do not allow their country settings to be altered.
*NCnn Country select
27 South Africa
19 Czech Republic
22 United States
Note : Use the Interactive Manual to setup the country.
Range : 0 to 255
S1 Ring counter
S1 is incremented each time the modem detects a ring signal on the telephone line.
Range : 0 to 255
S2 Escape character
S2 holds the decimal value of the ASCII character used as the escape sequence. A value over 127 disables the escape process.
Range : 0 to 127 (Default = 43)
S3 Carriage Return Character
Sets the command line and result code terminator character. Pertains to asynchronous operation only.
Range : 0 to 127 ASCII decimal (Default=13)
S4 Line feed Character
Sets the character recognised as a line feed. Pertains to asynchronous operation only.
Range : 0 to 127 ASCII decimal (Default=10)
S5 Backspace Character
Sets the character recognised as a backspace.
Range : 0 to 32 ASCII decimal (Default=8)
S6 Wait for dialtone
Sets the time in seconds that the modem will try to detect a dialtone (if set) and wait before starting to dial.
Range : 2 to 255 seconds
S7 Wait for Carrier after dial
Sets the time in seconds that the modem will wait for a carrier before hanging up.
Range : 1 to 255 seconds
S8 Pause time for delay
Sets the time the modem must pause when the , dial modifier is used.
Range : 0 to 255 seconds
S9 Carrier detect response time
Sets the time in 10th of a second, that the carrier must be present before the modem considers it valid and turns on RLSD.
Range : 1 to 255 tenths of a second.
S10 Lost carrier to Hang-up delay
Sets the time in 10th of a second, that the modem waits before hanging up after a loss of carrier.
Range : 1 to 255
S11 DTMF Tone duration
Range : 50 to 255 milliseconds (Default=95)
S12 Escape Prompt Delay
Defines the maximum period, in fifties of a second, allowed between receipt of the last character of the three escape character sequence and the sending of the OK message.
Range : 0 to 255 1/50 of a second
S18 Test timer
Sets the length in seconds that the modem conducts a test.
Range : 0 to 255 seconds
S25 Delay to DTR
Sets the time that the modem will ignore DTR before taking action specified by &Dn.
Range : 0 to 255 seconds
S26 RTS to CTS delay
Sets the time delay, before the modem turns on CTS after detecting an OFF-ON transition on RTS when &R0 is commanded.
Range : 0 to 255 hundredths of a second
S32 XON Character
Range : 0 to 255 ASCII decimal (Default=17)
S33 XOFF Character
Range : 0 to 255 ASCII decimal (Default=19)
S38 Delay Before Forced Hang-up
This register sets the delay between the modems receipt of the H command to disconnect and the disconnect operation.
Range : 0 to 255 seconds
S86 Call Failure Reason Code
When the modem issues a NO CARRIER result code, a value is written to this S-register.
Range : 0,4,5,9,12,13 or 14
0 Normal disconnect, no error occurred
4 Loss of carrier
5 V.42 negotiation failed
9 The modems could not find a common protocol
12 Normal disconnect initiated by the remote modem
13 Remote modem does not respond after 10 re-transmissions of the same message.
14 Protocol violation
S91 PSTN Transmit level Attenuation
Sets the transmit level attenuation level from 0 to 15dBm for the PSTN mode. Some countries may not permit changing the transmit level.
Range : 0 to 15dBm (Corresponding to 0 to -15dBm transmit level)
Default : 10dBm
S95 Extended Result Codes
Bit 0 Connect message indicates DCE speed
Bit 1 Append /ARQ to CONNECT XXXX
Bit 2 Enable CARRIER XXXX message
Bit 3 Enable PROTOCOL message
Bit 4 Reserved
Bit 5 Enable COMPRESSION XXXX
Bit 6 Reserved
Bit 7 Reserved