Modem AT Command Set

US Robotics AT Command Set

The Hayes Command Set

This is the Basic and Extended Hayes Command Set. The modem initialization string consists of a series of commands. It prepares the modem for communications, setting such features as dialing mode, waits, detection of the busy signal and many other settings. For many years Hayes modems have been the standard in modems. As the field of modem manufactures has grown, most have adhered at least losely to the Hayes standard. The following is a partial list of the Hayes command set. (called the AT commands). The Hayes Command Set can be divided into three groups:

Basic Command Set - A capital character followed by a digit. For example, M1.
Extended Command Set - An "&" (ampersand) and a capital character followed by a digit. This is an extension of the basic command set. For example, "&M1". Note that "M1" is different from "&M1".
Register Commands - Sr=n where "r" is the number of the register to be changed and "n" is the new value that is being assigned. A "register" is computerese for a specific physical location in memory. Modem have small amounts of memory onboard. This third set of commands is used to enter values in a particular register (memory location). The register will be storing a particular "variable" (alpha-numeric information) which is utilizedby the modem and communication software. For example, S7=60 instructs your computer to " Set register #7 to the value 60."

Here are some of the most important characters that may appear in the modem initialization string. These characters normally should not be changed.

Basic Characters
AT	Tells the modem that modem commands follow. This must begin each line of commands.
Z	Resets the modem to default state
~	Makes your software pause for half a second. You can use more than one ~ in a row. For example, "~~~~" tells the software to pause two seconds.
^M	Sends the terminating Carriage Return character to the modem. This is a control code that most communication software translate as a "carriage return."

AT Help Commands
AT$	HELP, Command Quick Reference (CTRL-S to Stop, CTRL-C to Cancel)
AT&$	HELP, Ampersand Commands
ATD$	HELP, Dial Commands
ATS$	HELP, S Registers

AT Quick Reference
Command	Description
AT	Procedes all modem action commands.
ATDTnnnnnnn	Dial the nnnnnnn telephone number using Touch-Tone dialing.
ATDPnnnnnnn	Dial the nnnnnnn telephone number using Pulse dialing.
ATA	Answer an incoming call.
ATH0	Hang up immediately.
AT&F	Reset the modem to factory default settings.
ATZ	Reset the modem to its power-up settings, which may include modifications made by the user.

A/	Re-execute command.
ATBn	Set CCITT or Bell Mode. B0 Selects CCITT V.22bis, V.22, and V.21 standards for communication at 2400, 1200, and 300 bps. B1 Selects Bell 212A and 103 standards for communication at 1200 and 300 bps (default)
ATCn	Carrier control. C0 - return error code. C1 - normal transmit carrir switching (default).
ATI0 - ATI11	Modem query commands.
AT+FCLASS=?	If the modem is Class 1 then the response from the modem to this command will return a string 0,1,1.0. If the modem is Class 1 and Class 2 the response will be 0,1,2, 1.0

The Basic Hayes Command Set - Alphabetical

AT$ - HELP, Command Quick Reference (CTRL-S to Stop, CTRL-C to Cancel)
&$  - HELP, Ampersand Commands
A/ - Repeat last executed command. Use primarily to redial, AT nor [Rtrn] required
AT - Required Command mode prefix (Attention Modem)
A - Answer Call
Bn - n=0 V32 Mode/CCITT ans Seq
	n=1 Bell Answer Seq
	n=2 Verbose/Quiet On Answer
Dn - Dial a Telephone Number
	n=0..9#*TPR,;"W@!()- 
DL - Dial Last Phone Number
DSn - Dial Stored Phone Number
D$ - HELP, Dial Commands 
En - n=0 No Command Echo 
	n=1 Echo Command Chars
Fn -
	n=0 Online Echo
	n=1 No Online Echo
Hn
	n=0 On Hook (Hang Up)
	n=1 Off Hook
In
	n=0 Product Code
	n=1 Checksum
	n=2 RAM Test
	n=4 Current Settings
	n=5 NVRAM Settings
	n=6 Link Diagnostics
	n=7 Product Configuration
Ln
	n=0 Low Speaker Volume
	n=1 Low Speaker Volume
	n=2 Med Speaker Volume
	n=3 Hi Speaker Volume
Mn
	n=0 Speaker Off
	n=1 Speaker OnUntil CD
	n=2 Speaker Always On
	n=3 Speaker Off During Dial
On
	n=0 Return Online
	n=1 Return Online & Retrain
P - Pulse Dial
Qn
	n=0 Result Codes Sent
	n=1 Quiet (No Result Codes)
Sr=n - Sets Register "r" to "n"
Sr? - Query Register "r"
S$ - HELP, S Registers
T - Tone Dial 
Vn
	n=0 Numeric Responses
	n=1 Verbal Responses
Xn
	n=0 Basic Result Codes
	n=1 Exended Result Codes
	n=2-4 Advanced Result Codes
Yn - Select power on/reset default configuration
	n=0 Next reset to &W0 settings
	n=1 Next reset to &W1 settings
Zn - Reset modem based on current DIP switch settings
	n=0 Dipswitch #7 determines reset
	n=1 Reset to &W0 settings
	n=2 Reset to &W1 settings
	n=3 Reset to &F0 settings
	n=4 Reset to &1 settings
	n=5 Reset to &F2 settings
+++ - Escape Code

The Extended Hayes Command Set (Ampersand Commands)

AT&$ - HELP, Ampersand Commands
&An
	n=0 Disable /ARQ Result Codes
	n=1 Enable /ARQ Result Codes
	n=2 Enable /Modulation Codes
	n=3 Enable /Extra Result Codes
&Bn
	n=0 Floating DTE Speed
	n=1 Fixed DTE Speed
	n=2 DTE Speed Fixed When ARQ
&Cn
	n=0 CD Always On
	n=1 Modem Controls CD
&Dn
	n=0 Ignore DTR
	n=1 On-Line Command Mode
	n=2 DTE Controls DTR
&Fn
	n=0 Load Factory 0, no FC
	n=1 Load Factory 1, HW FC
	n=2 Load Factory 2, SW FC
&Gn
	n=0 No Guard Tone
	n=1 550 Hz Guard Tone
	n=2 1800 Hz Guard Tone
&Hn
	n=0 Disable TX Flow Control
	n=1 CTS
	n=2 Xon/Xoff
	n=3 CTS and Xon/Xoff
&In
	n=0 Disable RX Flow Control
	n=1 Xon/Xoff
	n=2 Xon/Xoff Chars Filtered
	n=3 HP Enq/Ack Host Mode
	n=4 HP Enq/Ack Terminal Mode
	n=5 Xon/Xoff for non-ARQ Mode
&Kn
	n=0 Disable Data Compression
	n=1 Auto Data Compression
	n=2 Enable Data Compression
	n=3 Selective Data Compression
&Mn
	n=0 Normal Mode
	n=4 ARQ/Normal Mode
	n=5 ARQ Mode
&Nn
	n=0 Highest Link Speed
	n=1 300 bps
	n=2 1200 bps
	n=3 2400 bps
	n=4 4800 bps
	n=5 7200 bps
	n=6 9600 bps
	n=7 12000 bps
	n=8 14400 bps
&Pn
	n=0 N.American Pulse Dial
	n=1 UK Pulse Dial
&Rn
	n=1 Ignore RTS
	n=2 RX to DTE/RTS high
&Sn
	n=0 DSR Always On
	n=1 Modem Controls DSR
&Tn
	n=0 End Test
	n=1 Analog Loopback (ALB)
	n=3 Digital Loopback (DLB)
	n=4 Grant Remote DLB
	n=5 Deny Remote DLB
	n=6 Remote Digital Loopback
	n=7 Remote DLBWith Self Test
	n=8 ALB With Self Test
&Wn
	n=0 Store Configuration 0
	n=1 Store Configuration 1
&Yn
	n=0 Destructive
	n=1 Destructive/Expedited
	n=2 Nondest./Expedited
	n=3 Nondest./Unexpedited
&Zn=s - Store Phone Number
&Zn? - Query Phone Number