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              Outbreak Magazine Issue #11 - Article 15 of 18
           '~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~'

The Hayes Modem Command Set
---------------------------
by: Magickal1


Here is a description of the Hayes Command Set. Most modems follow this 
command set to large extent. If you lost your modem manual or never had 
one in the first place, this reference might come in handy. I for 
instance finally found out how to turn my modems speaker off: ATM0 -- 
Finally: Silence!


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. Newer 
modem communications programs reset the initializations string for you 
according to which menu options you select, which features you enable, 
etc..

For many years Hayes modems have been the standard. As the field of 
modem manufactures has grown, most have adhered at least loosely 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 
four 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.

Proprietary Command Set

Usually started by either a backslash ("\"), or a percent sign ("%"), 
these commands vary widely among modem manufacturers. For that reason, 
only a few of these commands are listed below.

Register Commands

Sr=n where r is the number of the register to be changed, and n is the 
new value that is assigned.


A "register" is computerese for a specific physical location in memory. 
Modems have small amounts of memory onboard. This fourth 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 utilized by the modem and communication software. For 
example, S7=60 instructs your computer to "Set register #7 to the value 
60".


Note


Although most commands are defined by a letter-number combination (L0, 
L1 etc.), the user of a zero is optional. In this example, L0 is the 
same as a plain L. Keep this in mind when reading the table below!


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

AT

Tells the modem that modem commands follow. This must begin each line 
of commands.

Z

Resets the modem to it's default state

, (a comma)

makes your software pause for a second. You can use more than one , in 
a row. For example, ,,,, tells the software to pause four seconds. (The 
duration of the pause is governed by the setting of register S8.

^M

Sends the terminating Carriage Return character to the modem. This is a 
control code that most communication software translates as "Carriage 
Return"


The Basic Hayes Command Set

In alphabetical order:


Table B.1. Basic Hayes Command Set


Command		Description		Comments


A0 or A		Answer incoming call	
 
A/		Repeat last command	Don't preface with AT. Enter usually aborts.

B0 or B		Call negotiation	V32 Mode/CCITT Answer Seq.

B1		Call negotiation	Bell 212A Answer Seq.

B2		Call negotiation	Verbose/Quiet On Answer

D		Dial			Dial the following number and then handshake in orginate 
mode.

					P	Pulse Dial

					T	Touch Tone Dial

					W	Wait for the second dial tone

					,	Pause for the time specified in register S8 (usually 2 
seconds

					;	Remain in command mode after dialing.

					!	Flash switch-hook (Hang up for a half second, as in
transferring a call.

					L	Dial last number

E0 or E		No Echo			Will not echo commands to the computer

E1		Echo			Will echo commands to the computer (so one can see what one 
types)

H0		Hook Status		On hook - Hang up

H1		Hook status		Off hook - phone picked up

I0 or I		Inquiry, Information, or Interrogation
						This command is very model specific. I0 usually returns a
number or code, while higher numbers often provide much more 						
useful information.

L0 or L		Speaker Loudness. Modems with volume control knobs will not 
have these options.
Off or low volume

L1		Low Volume

L2		Medium Volume

L3		Loud or High Volume

M0 or M		Speaker off			M3is also common, but different on many brands


M1						Speaker on until remote carrier detected (i.e. until the
other modem is heard)


M2						Speaker is always on (data sounds are heard after CONNECT)


N0 or N		Handshake Speed			Handshake only at speed in S37


N1						Handshake at highest speed larger than S37

O0 or O		Return Online			See also X1 as dial tone detection may be 
active.

O1						Return Online after an equalizer retrain sequence


Q0 or Q1	Quiet Mode			Off - Displays result codes, user sees command 
responses 						(e.g.OK)

Q1		Quiet Mode			On - Result codes are suppressed, user does not see
responses.

Sn?						Query the contents of S-register n

Sn=r		Store				Store the value of r in S-register n

V0 or V		Verbose				Numeric result codes

V1						English result codes (e.g.CONNECT, BUSY, NO CARRIERetc.)

X0 or X		Smartmodem			Hayes Smartmodem 300 compatible result codes

X1						Usually adds connection speed to basic result codes 
(e.g.CONNECT 1200

X2						Usually adds dial tone detection (preventing blind dial, and 
sometimes preventing AT0)

X3						Usually adds busy signal detection

X4						Usually adds both busy signal and dial tone detection

Z0 or Z		Reset				Reset modem to stored configuration. Use Z0, Z1etc. 
for 						multiple profiles. This is the same as &F for factory
						default on modems without NVRAM (non voltaile memory)

The Extended Hayes Command Set


Ampersand Commands


Table B.2. The Extended Hayes Command Set

Command			Description		Comments

&B0 or &B		Retrain Parameters	Disable auto retrain function

&B1			Retrain Parameters	Enable auto retrain function

&B2			Retrain Parameters	Enable auto retrain, but disconnect if no line 
improvement 						over the period dictated by S7

&C0 or &C1		Carrier detect		Signal always on

&C1			Carrier detect		Indicates remote carrier (usual preferred 
default)

&D0 or &D		Data Terminal Ready(DTR Signal ignored (This is modem 
specific, you must see 						your manual for information on this one!)

&D1			Data Terminal Ready(DTR	If DTR goes from On to Off the modem goes 
into command mode 						(Some modems only)
&D2			Data Terminal Ready(DTR	Some modems hang up on DTR On to Off 
transition (This is the 						usual preferred default)
&D3			Data Terminal Ready(DTR	Hang up, reset the modem, and return to 
command mode upon DTR

&F0 or &F		Factory defaults	Generic Hayes-compatible defaults. 
						This is usually a good thing to use in your init string,
          					since the &F1-&F3 settings can vary among modems, and they 
						may actually be the cause of connection problems. 
						(Since you never know exactly what Brand X's &F2 really changes.

						On the other hand, it pays to try out the other options
						below; many people's problems can be solved by replacing a 
						complicted init string with a simple &F2 or the like.  However, if 
						building an init string, it's best to start with a simple &F, and not 
						use the "customized" form of defaults.

&F1			Factory Defaults	Factory Defaults tailored to an IBM PC 
compatible user

&F2			Factory Defaults	Factory defaults for a Mac w/software 
handshaking

&F3			Factory Defaults	Factory defaults for a Mac w/hardware 
handshaking

&G0 or &G		Guard tones		Disable guard tones

&K0 or &K		Local flow control	Disable local flow control

&K1			Local flow control	Enable RTS/CTS hardware local flow control

&K2			Local flow control	Enable XON/XOFF software local flow control

&K3			Local flow control	Enable RTS/CTS hardware local flow control

&K4			Local flow control	Enable XON/XOFF software local flow control

&L0 or &L		Dial mode		Select dial-up mode

&M0 or &M		Error control mode	Select asynchronous non-EC mode (the same 
as &Q0)

&P0 or &P		Pulse dialing ratio	U.S./Canada pulse dialing 39% make / 61% 
break ratio

&P1			Pulse dialing ratio	U.K./Hong Kong pulse dialing 33% make / 67% 
break ratio

&Q0 or &Q		Error control mode	Asynchronous non-EC more. No data 
buffering. ASB disabled.

&Q5			Error control mode	Select V.42 EC operation (requires flow 
control)

&Q6			Error control mode	Asynchronous mode with ASB (requires flow 
control)

&Q8			Error control mode	Select alternate EC protocol (MNP)

&Q9			Error control mode	Conditional data compression: V.42bis = yes, 
MNP5 = no.

&S0 or &S		DSR action select	Always on (default)

&S1			DSR action select	Follows EIA specification (Active following 
carrier tone, 						and until carrier is lost.)

&T0 or &T		Self test		Model specific self test on some modems

&U0 or &U		Trellis code modulation	Enable V.32 TCM

&U1			Trellis code modulation	Disable V.32 TCM

&V0 or &V1		View active		(and often stored) configuration profile 
settings (or ATI4

&W0 or &W		Store profile		In NVRAM (&W0, &W1 etc. for multiple 
profiles) Some settings cannot be stored. These often don't show on &V or 
ATI4

&Y0 or &Y		Select configuration loaded at power-up			Load profile 0 
(default)

&Y1			Select configuration loaded at power-up			Load profile 1

&Zn=x			Soft reset and load stored profile number n		Note that all 
items after the &Z on the command line are ignored

Backslash and Percent Commands


Table B.3. Backslash and Percent Commands


Command			Description				Comments


\A0 or \A		Character maximum MNP block size	64 character maximum

\A1			Character maximum MNP block size	128 character maximum

\A2			Character maximum MNP block size	192 character maximum

\A3			Character maximum MNP block size	256 character maximum

%C0 or %C		Data Compression Enable/Disable		Disabled

%C1			Data Compression Enable/Disable		MNP5 enabled

%C2			Data Compression Enable/Disable		V.42bis (BTLZ) Enabled

%C3			Data Compression Enable/Disable		MNP5 & V.42bis (BTLZ) Enabled

%D0 or %D		Data compression			512 BLTZ dictionary size

%D1			Data compression			1024 BLTZ dictionary size

%D2			Data compression			2048 BLTZ dictionary size

%D3			Data compression			4096 BLTZ dictionary size

%E0 or %E1		Escape method				ESCAPE DISABLED

%E1			Escape method				+++AT method (default)

%E2			Escape method				BreakAT method

%E3			Escape method				BOTH methods enabled

%E4			Escape method				Disable OK to +++

%E5			Escape method				Enable OK to +++

\J0 or \J		DTE Auto Rate Adjustment		Disabled

\J1			DTE Auto Rate Adjustment		DTE rate is adjusted to match carrier 
rate.

\N0 or \N		Connection type				Normal connection (see below for 
definitions)

\N1			Connection type				Direction connection

\N2			Connection type				MNP Auto-reliable connection

\N3			Connection type				Auto-reliable connection

\N4			Connection type				V.42bis reliable link with phase detection

\N5			Connection type				V.42bis auto-reliable link with phase
detection

\N6			Connection type				V.42 reliable link with phase detection

\N7			Connection type				V.42 auto-reliable link with phase detection

A direct connection is a simple straight-through connection without any 
error connection or data compression. In this case, the 
computer-to-modem and modem-to-modem speeds must be identical.

A normal connection uses flow control (either software or hardware) to 
buffer the data being sent or received, so that the modem can transmit 
data at a different rate than the computer is actually sending or 
receiving it. For example, a computer may send actual data at 57kbps, but 
using compression, the modem only actually sends 28.8kbps. This is the 
mode use by most modems.

A reliable connection is a type of normal connection; if, for some 
reason, data compression or error correction cannot be established or 
maintained, the connection will hang up. (In essence, such a modem ensures 
that all connections are reliable, for it will hang up if the connection 
isn't.)

Likewise, an auto-reliable connection is virtually the same, except 
that the modem will try to renegotiate the connection in order to 
establish a reliable connection. Again, this is the mode that most modems use.


S-Registers

Table B.4. S Registers

Register	Range				Default	Function

S0		0-255 rings			1-2	Answer on ring number. Don't answer if 0

S1		0-255 rings			0	if S0 is greater than 0 this register counts the
incoming rings.

S2		0-127 ASCII			43 +	Escape to command mode character

S2		>127					no ESC

S3		0-127 ASCII			13 CR	Carriage return character

S4		0-127 ASCII			10 LF	Line feed character

S5		0-32, 127 ASCII			8 BS	Backspace character

S6		2-255 seconds			2	Dial tone wait time (blind dialling, see Xn

S7		1-255 seconds			30-60	Wait time for remote carrier

S8		0-255 seconds			2	Comma pause time used in dialing

S9		1-255 1/10ths second		6	Carrier detect time required for 
recognition

S10		1-255 1/10ths second		7-14	Time between loss of carrier and hangup

S11		50-255 milliseconds		70-95	Duration and spacing of tones when tone 
dialing

S12		0-255 1/50th seconds		50	Guard time for pause around +++ command 
sequence

S36		Fallback options when error correction link fails:

						7	Negotiation Failure Treatment

		0 - Disconnect

		1 - Establish Direct Connection

		3 - Establish Normal Connection	

		4 - Establish an MNP connection if possible, else disconnect

		5 - Establish an MNP connection if possible, else Direct Connection.

		7 - Establish an MNP connection if possible, else Normal connection

						
S37		1 = 300 bps			0	Negotiation Speed (Intial handshake)

		5 = 1200 bps
	
		6 = 2400 bps

		7 = 1200/75 bps (v.23 mode)
		
		8 = 4800 bps

		9 = 9600 bps

		10 = 12000 bps

		11 = 14400 bps

		12 = 7200 bps

Many modems have dozens, even hundreds, of S registers, but only the 
first dozen or so are fairly standard. They are changed with a command 
like ATSn=N, and examined with ATSn? (e.g. AT S10=70 S1? would tell the 
modem not to hang up for seven seconds should it not hear the answering 
modem, and return the number of times the phone last rang.)
