Chapter 3 - AT Commands
3.2.2 Command Structure
You can control a wide variety of modem operations and options when the modem is in command mode. AT commands tell the modem to dial a number, to answer a call, to operate at a certain speed, to use a certain compression technique, and many other functions. AT commands consist of one or two letters, which may be preceded by an ampersand (&), a dollar character ($), a pound character (#), a percent character (%), or a greater-than character (>). The Q command, for example, determines whether the modem returns result codes, while the &Q command selects which AT command set the modem uses.
A parameter after a command (0, 1, 2, etc.) tells the modem which option to use. If you do not specify a parameter, the modem assumes the 0 (zero) option. E, for example, is the same as E0. You can issue several commands on a single line (a command string) as long as the line does not exceed 60 characters. Note that though Q1 is one command, it counts as two characters in the command line.
Each command has a valid range of parameters; for instance, &W can have only 0 or 1 as a parameter. Valid commands generate an OK result code. A few generate an additional response, such as a list of parameters.
An invalid command, such as &W3, which has a parameter outside the valid range, generates an ERROR result code. Most commands have a default parameter, one that is enabled when the modem is turned on or reset with the ATZ or AT&F command. Factory defaults are stored in read-only memory (ROM), and cannot be changed. User-defined defaults can be stored in nonvolatile random-access memory (NVRAM), and can be changed or deleted at will.
3.3.3 Command Editing
Always begin a command with the letters AT. You may type the command in upper case or lower case, but not both. The AT command is not executed until you press the ENTER key. Use the BACKSPACE key to erase the previous command character; it will not erase the AT characters once they are typed. If your keyboard has no BACKSPACE key, use CTRL+H. You can change the character recognized by the modem as BACKSPACE to any other ASCII character by changing register S5.
To cancel an entire command that has been typed but not yet executed, press CTRL+X. This also clears the command buffer. The effect is the same as backspacing the command, only quicker.
The MT2834MR6 stores characters entered in a command in the modem’s command buffer until they are executed by pressing ENTER. The command buffer’s capacity is 60 characters. The attention characters (AT) do not count in the 60 allowed command characters. You may use spaces for increased readability when typing a command; they are neither stored in the command buffer nor counted in the 60 allowed characters.
Hyphens, parentheses, etc., are not allowed.
If you exceed the 60-character limit or type invalid characters, the command buffer is automatically erased and an ERROR message is displayed. You must then retype the command within the 60-character limit, using only the allowed characters.
The commands in this chapter are organized by function. A brief summary follows.
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Chapter 3 - AT Commands
Table 3-1. AT Commands by Function
Topic:
Dialing Action
Command:
D
A:
H
Dial Modifiers
!
;
:
,
P
T
W
R
@
$
Phone Number
Memory
Configuration
Storage & Recall
Modem Responses
(Result Codes)
Online Connection
E
Q
&Q
V
X
&A
#A
B
%DC
&CD
>DT
#F
&G
*H
&P
&RD
$T
#T
Y
D...N
N
N...N
L
&W
&F
Z
Description:
Dial
Continuous redial
On-hook/off-hook
Pulse dialing
Tone dialing
Wait for new dial tone
Reverse originate/answer mode
Dialing pause
Continuous redial
Return to command mode after dialing
Flash on-hook
Quiet answer
Call card tone detect
Store a phone number
Dial a stored number
Number linking
List stored telephone numbers
Store configuration
Load default configuration
Reset modem
Echo command mode characters
Result codes: enable/disable
Result codes: Multi-Tech or standard
Result codes: verbose/terse
Result codes and call progress
Answerback
Auto speed detection
Answer tone
Command mode control
Cleardown at disconnect
DTMF detection
Fallback modes when online
Guard tones
Busy-Out After Disconnect
Pulse dial ratios
Square wave ring detect
Calling tones
Trellis-coded modulation
Long space disconnect
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Chapter 3 - AT Commands
Table 3-1. AT Commands by Function (con't)
Topic:
V.34 Controls
Command:
%F
&RA
#V
Description:
Echo canceler frequency offset comp.
Asymmetric bit rate
V.32terbo handshake
RS-232 Interface
Controls
Error Correction &
Data Compression
Speed Controls
&C
&D
&R
&S
&RF
&SF
&E0
&E1
&E2
&E14
&E15
#L
$E
$A
$F
$R
$BA
$MB
$SB
Carrier Detect control
Data Terminal Ready control
Clear to Send control
Data Set Ready control
CTS/RTS interaction control
DSR/CD interaction control
Non-error correction mode
Autoreliable mode
Reliable mode
Data compression disabled
Data compression enabled
V.42 error correction modes
V.42 error correction at 300 bps
Autoreliable buffering
Autoreliable fallback character enable
Retransmit count
Baud adjust
Modem baud rate
Serial port baud rate
Immediate Action
Flow Control &BS
$EB
&E3
&E4
&E5
&E6
&E7
&E8
&E9
I
A/
L5
L6
L7
L8
&RN
&RR
Repeat last command
Inquire product code
List current operating parameters
List S-register values
List current operating parameters
List online diagnostics
Rate renegotiation
Retrain
Maximum reliable block size
Asynchronous word length (10/11-bit)
Flow control disabled
Hardware flow control
XON/XOFF flow control
XON/XOFF no pass-through
XON/XOFF pass-through
Hewlett Packard ENQ/ACK pacing off
Hewlett Packard ENQ/ACK pacing on
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Chapter 3 - AT Commands
Table 3-1. AT Commands by Function (con't)
Topic: Command:
&E10
&E11
&E12
&E13
#X
Description:
Non-error correction mode flow control off
Non-error correction mode flow control on
Pacing off
Pacing on
Number of XOFF characters sent
Escape
Sequences
Remote
Configuration
+++AT<CR>
<BREAK>AT<CR>
%E
A
O
Default in-band escape sequence
Alternate out-of-band escape sequence
Escape sequence selection
Force answer mode
Go back online
%%%AT<CR> Remote configuration escape sequence
#I Change login password
#S Change setup password
Line Probes
Diagnostics
%DP
%DF
&RP
L9
L10
L11
&T
U
Read line probe data
Format line probe data
Immediate line probe
Display signal strength
Display signal to noise ratio
Display noise strength
Respond to remote digital loopback signal
Loopback test modes
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