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Description/Dissection of AT Commands used in Init Strings

%Cn -- Enable/Disable Data Compression
%En -- Auto-Retrain control
&Cn -- DCD Control
&Dn -- DTR Option
&Fn -- Recall Factory Profile
&Gn -- Select Guard Tone
&Kn -- Data Flow Control (Most non-US Robotics Modems)
&Kn -- Enables/Disables Data Compression (Texas Instruments, US Robotics)
&Qn -- Communication (Sync/Async Mode)
&Rn -- RTS/CTS (Hardware) Flow Control
&Tn -- Test Mode
&V -- View Configuration
&Wn -- Store User Profile
&Yn -- Default User Profile
&Zn=x -- Store Phone Number
)Mn -- Cellular Power Level Adjustment
*Hn -- Link Negotiation Speed
+++ -- Escape Sequence
+MS -- Select Modulation
:En -- Compromise Equalizer Setting
? -- Read Currently Selected S Register
@Mn -- Initial Cellular Power Level Setting
\An -- Select Maximum MNP Block Size
\Bn -- Transmit Break
\Gn -- Modem to Modem (Software) Flow Control
\Ln -- Select MNP Block/Stream Mode
\Nn -- Protocol Negotiation Selection
A -- Answer
A/ -- Re-execute Command
Bn -- CCITT or Bell Selection
Cn -- Carrier Control
Dn -- Dial
En -- Command Echo
Fn -- Select Modulation
Hn -- Disconnect (Hang-up)
In -- Identification
Ln -- Speaker Volume
Mn -- Speaker Control
Nn -- Automode Enable (Automatic Line Speed Detection)
On -- Return to On-Line Data Mode
P -- Set Pulse Dial Default
Qn -- Result Code On/Off
Sn -- Select a Specific S Registe
Sn=x -- Write an S Register Value
Sn? -- Read an S Register
T -- Set Tone Dial Default
Vn -- Result Code Format
Wn -- Negotiation Progress (Connect Message) Control
Xn -- Extended Result Code
Yn -- Long Space Disconnect
Zn -- Modem Reset
+++ (Escape Sequence)

A/ (Re-execute Command)
This command re-executes the previous command processed by the modem.

In (Identification)
This command instructs the modem to return its product identification information.
I0 -- Returns the product code.
I1 -- Reports the 3 digits pre-computed ROM checksum code.
I2 -- Calculates a checksum of the modem firmware ROM and indicates OK or ERROR for the checksum validity.
I3 --Returns the modem ROM version.
I4 -- TBD
I5 -- TBD
I6 -- Returns the modem data pump model.
Easiest way to view this information on a win95/98 machine is to go to the control panel, modems, highlight your modem, click diagnostics, highlight the port the modem is on, and click more info. This will show you the whole range of ATI commands and is of great help when faced with trying to figure out what kind of modem is in your machine and possibly the driver of that modem.

Zn (Modem Reset)
This command resets the modem and recalls the stored configuration as defined at power on time.
Z0 -- Reset and recall stored user profile 0.
Z1 -- Reset and recall stored user profile 1.
Most usually only ATZ is used.

&Fn (Recall Factory Profile)
This command reloads the factory default profile.
&F0 -- Recall Factory Profile 0. Factory Profile 0 contains the default values from the modem chipset supplier.
&F1 -- Recall Factory Profile 1. Factory Profile 1 contains the default values defined by the product manufacturer.

Ln (Speaker Volume)
L0,1 -- Selects low speaker volume.
L2 -- Selects medium speaker volume.
L3 -- Selects high speaker volume.

Mn (Speaker Control)
M0 -- The speaker is always off.
M1 -- Enables the speakerduring call establishment, but off once the carrier is detected.
M2 -- The speaker is always on.
M3 -- Disables the speaker during the dialing period and receiving carrier, but on during answering.

&Dn (DTR Option)
This command controls the modem response to the serial port's Data Terminal Ready (DTR) signal.
This command interprets the ON and OFF transitions of the DTR signal from the DTE in accordance with the parameters as defined by n.

&Kn (Data Flow Control on most non US Robotics modems)
This command determines how the modem controls data flow between the system and the modem. For example, if the speed between the system unit and the modem is 19200 bps, and the speed between the local and remote modem is 2400 BPS, the transmit buffer of the modem is likely to be overflow when the system is sending large amounts of data. To prevent an overflow and subsequent loss of data, the modem either sends a XOFF character or drops the CTS signal to signal that the system should stop data sending. When enough space is available in the modems transmit buffer, the modem either sends a XON character or raises CTS to signal that application could resume data sending. For binary data transfer CTS/RTS flow control should be selected since the modem cannot distinguish the user's data from XON/XOFF characters. Flow control is not used for direct mode connection.
&K0 -- Disables flow control.
&K1 -- Error
&K2 -- Error
&K3 -- Enables RTS/CTS flow control. Flow control is active in both sending and receiving direction.
&K4 -- Enables XON/XOFF flow control. Flow control is active in both sending and receiving direction.
&K5 -- Enables transparent XON/XOFF flow control. XON/XOFF character which is sent from the system unit will be processed for flow control and also sent to the remote modem. Flow control is active in both sending and receiving direction.
&K6 -- Enables both RTS/CTS and XON/XOFF flow control.

&Kn (Enables/Disables Data Compression on Texas Instruments/US Robotics modems)
&K0 -- Data Compression Enabled &K1 -- Auto Enabled/Disabled &K2 -- Data Compression Enabled &K3 -- MNP5 Compression Disabled

&Rn (RTS/CTS (Hardware) Flow Control)
This command determines how the modem controls CTS (Clear to Send). CTS operation is modified if hardware flow control is selected.
&R0 -- In synchronous mode, CTS tracks the state of RTS. In asynchronous mode, CTS acts according to V.25 handshake.
&R1 -- In synchronous mode, CTS is always ON (RTS transitions are ignored). In asynchronous mode, CTS will only drop if required by flow control.

+MS - Select Modulation
This extended-format command selects the modulation and, optionally, enables or disables automode, specifies the lowest and highest connection rates.
The command format is:
+MS=11,1 disables k56flex and V.90 on some Rockwell modems and enables V.34 (33.6)
+MS=V34 disables V.90 on some Rockwell HCF chipset modems and enables V.34 (33.6)
+MS=k56flex disables V.90 on some Rockwell HCF chipset modems and enables k56flex
+MS=V90 enables V.90 on some Rockwell HCF chipset modems.

&V (View Configuration)
This command displays the current active configuration, stored user profiles, and the first four stored telephone numbers.

&Cn (DCD Control)
This command controls the behavior of the DCD (Data Carrier Detect) signal of the internal serial port.
&C0 -- DCD is always on.
&C1 -- DCD will track the state of the data carrier from the remote modem.

&Wn (Store User Profile)
&W0 -- Store active configuration as user's profile 0.
&W1 -- Store active configuration as user's profile 1.

Dn (Dials the specified phone number). Includes the following:
         L           Dials the last dialed number.

         P           Pulse (rotary) dial

         R           Originates call using answer (reverse) frequencies.

         Sn          Dials the phone number string stored in NVRAM at
                     position n (n = 0*3). Phone numbers are stored with the
                     &Zn=s command.

         T           Tone dial

         ,           (Comma) Pause, See S8 definition; which it?s linked to.

         ;           (Semicolon) Return to Command mode after dialing.

         "           Dials the letters that follow (in an alphabetical phone

         !           (Exclamation point) Flashes the switch hook.

         /           Delays for 125 ms. before proceeding with dial string.

         W           Wait for second dial tone (X2 or X4); linked to S6

         @           Dials, waits for quiet answer, and continues (X3 or higher).

         $           Displays a list of Dial commands.
eg: ATDP - Dials on a pulse line.
ATDT - Dials on a touch tone line.
ATDT5551234 dials 555-1234 on a touch tone line.

&Yn (Default User Profile)
&Y0 -- Selects power up configuration as user's profile 0.
&Y1 -- Selects power up configuration as user's profile 1.

&Zn=x (Store Phone Number)
This command stores up to 4 telephone number dial strings into one of 4 non-volatile memory locations specified by n.
n: Entry number (range 0-3)
x: dial string less than 45 digits (including dial modifiers)

&Gn=x (Sets the Guard Tone)
&G0 -- No Guard Tone, U.S. and Canada
&G1 -- 55o Hz Guard Tone, some European counties, requires B0 setting sometimes
&G2 -- 1800 Hz Guard Tone, U.K., requires B0 setting.

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