AT Commands A-M

		AT Commands A-M

This chapter describes all of the commands that are available when the modem is in data communications mode. Details of the environments in which they are used is given in previous chapters. See later chapters for descriptions of the applicable commands for fax and voice modes.

Where applicable, the associated options and default for each command is shown. The command line must start with 'AT' and be terminated by <Return> or <Enter>. More than one command may be entered on one line. If commands are entered without a parameter, 0 is assumed, e.g. ATH is equivalent to ATH0. If a parameter outside the permitted range is entered, the ERROR message is returned.

Note: The default settings for your modem may differ from those listed here. See the supplied Installation Guide for details of any differences.

Many AT commands alter the current configuration of the modem. These changes remain in effect until another AT command overrides the settings or the modem is reset. These customised settings can be saved within the modem's permanent memory as a user default by using the &W command which is described later. Use the &W command when you wish the modem to subsequently use your customised settings every time it is turned on or reset.

A Answer :

The A command forces the modem to check that the handset is in use or that RING has been detected. It then goes on-line in answer mode, gives out an answer tone and waits for a response. The modem returns the ERROR message if the above condition is not met. Once on-line the modem remains in answer mode for the period specified in register S7 before returning to local mode with the NO CARRIER message, or connecting to an incoming carrier and giving a CONNECT message.

The command is commonly used to switch from a previously established voice link to a data link so that data transfer can take place. The remote modem issues the D command. In this respect, the A and D act as a command pair and are used in conjunction with each other. The A command is not related to the automatic answer facility which allows the modem to respond automatically to incoming calls.

A/ Re-execute Command :

The modem behaves as though the last command line had been re-sent by the DTE. "A/" will repeat all the commands in the command buffer.

The principal application of this command is to place another call (using the Dial command) that failed to connect due to a busy line, no answer, or a wrong number. This command must appear alone on a command line. This command should not be terminated by a carriage return.

\A Maximum MNP block size :

Options : \A0, \A1, \A2, \A3 Default : \A3

The \A command defines the maximum data block size for an MNP error corrected link. Unless the line quality is particularly poor, larger block sizes produce better throughput.

\A0	selects 64 character maximum block size.
\A1	selects 128 character maximum block size.
\A2	selects 192 character maximum block size.
\A3	selects 256 character maximum block size.

B CCITT or Bell selection :

Options : B0, B1 Default : B0

This command selects Bell or CCITT (ITU-T) modulations for the line speed connections of 300 bps or 1200 bps according to the parameter supplied. Any other line speeds use CCITT (ITU-T) modulation standards.

B0	selects CCITT(ITU-T) modulations.
B1	selects Bell modulations (not normally used in the UK).

\B Transmit a break :

Options : \B1 to \B9 Default : N/A

The \B command forces the modem to transmit a BREAK to the remote system. For error corrected connections the \K command controls the behaviour of the modem in response to the \B command.

In non-error corrected mode the break length is specified by the number associated with the option. \B1 transmits a break length of 100ms, \B2 200ms and so on.

Under error corrected conditions the break length is not user selectable. If no connection is established the ERROR message is returned.

C1 Carrier Control :

This command is included for compatibility only, and has no effect other than returning a result code. The only valid parameter is 1.

%C Data compression select :

Options : %C0, %C1, %C2, %C3 Default : %C3

The %C command is used to set the data compression protocol on an error corrected link. See the chapter Error correction and data compression for further details.

%C0	Disables data compression.
%C1	Enables MNP5 data compression only.
%C2	Enables V.42bis data compression only.
%C3	Enables automatic selection of V.42bis or MNP5 data compression as appropriate.

&C DCD (Data Carrier Detect) option :

Options : &C0, &C1 Default : &C1

The DTE or communications software you run may require DCD to be enabled at times.

&C0	will force the DCD signal active irrespective of a valid incoming carrier.
&C1	will force DCD to follow the state of the incoming data carrier i.e. when a carrier is received DCD is made active.

#CID Caller ID :

Options : #CID?, #CID=?, #CID=0,1,2 Default : #CID=0

Enables or disables Caller ID.
#CID=0	Disables Caller ID. (Default.)
#CID=1	Enables Caller ID with formatted presentation to the DTE. The modem will present the data items in a pair format. The expected pairs are data, time, caller code (telephone number), and name. As shown below. RING DATE = 0220 TIME = 1255 NMBR = 01274-538000 RING RING
#CID=2	Enables Caller ID with unformatted presentation to the DTE. The modem will present the entire packet of information, excluding the leading U's, in ASCII printable hex numbers. As shown below. RING 801B11010101083032323031333031020C30313237342D35333830303057 RING RING
#CID?	Retrieves the current Caller ID mode from the modem.
#CID=?	Returns the mode capabilities of the modem in a list with each element separated by commas.

D Dial :

The D command instructs the modem to go on-line in originate mode. If followed by a telephone number your modem dials the number and waits for an answer tone from the remote modem. Upon receiving an answer tone, connection is attempted. If the connection is established, data transfer can take place.

A number of commands are also valid parameters within the dial string. These are described in detail in the Automatic dialling chapter. The commands are: 0-9 @ ^ (circumflex) , (comma) ! L P S=n ; (semi-colon) T W In addition, the * (star) and # (gate) characters can be used if recognised by your telephone exchange. However, these two characters can only be used when tone dialling.

Entering D by itself can be used to switch a previously established voice link to a data link (see the A command). The modem returns the ERROR message if the handset was not previously in use.

&D DTR (Data Terminal Ready) option :

Options : &D0, &D1, &D2, &D3 Default : &D2

This command determines the modem's response to ON-to-OFF transitions of the DTR signal from the DTE.

DTR drop is interpreted according to the current &Q setting as below:

&D0	&Q0, &Q5, &Q6 - DTR is ignored (assumed ON). Allows operation with computers which do not provide DTR.
&D1	&Q0, &Q5, &Q6 - DTR drop is interpreted by the modem as if the asynchronous escape sequence had been entered. The modem returns to asynchronous command mode without disconnecting.
&D2	&Q0, &Q5, &Q6 - DTR drop causes the modem to hang up. Auto answer is inhibited. This is the most convenient means of terminating a call in progress.
&D3	&Q0, &Q5, &Q6 - DTR drop causes the modem to perform a soft reset as if the Z command had been received. The &Y setting determines which profile is loaded.

E Echo select :

Options : E0, E1 Default : E1

The E command is used to enable or disable the echo of AT commands when in local mode. With echo enabled (E1) the modem echoes back commands sent from the DTE. If an echo facility within your DTE software is also enabled you will see two of each character entered as part of the command line. To avoid this either disable local echo within your DTE or issue the E0 (echo off) command to the modem.

With echo off and no DTE local echo the AT command lines that you enter are not visible.

%E Automatic retrain and rate change select :

Options : %E0, %E1, %E2, %E3 Default : %E2

This command controls whether the modem monitors the line quality and what action it takes when changes in line quality are detected. When %E1 is selected, if the line signal quality of a connection degrades to an unacceptable rate, a retrain (perform a new handshake and attempt to restart) is attempted. After three consecutive unsuccessful retrain attempts, the line is dropped. When %E2 is selected, the modem changes line speed to a higher (or lower) value depending on the receive signal quality.

%E0	disables automatic retrain.
%E1	enables automatic retrain.
%E2	enables automatic fall back and fall forward rate change.

F Communication mode select :

Options : F0, F1, F3 to F10, F13 to F21 Default : F0

The F command is used to preset the line speed. This is a fixed speed at which the connection must be established otherwise no connection is made at all. If automode (F0) is enabled all line speeds are available and connection is made at the highest common speed between both modems. See the chapter Baud rate control for more information.

F0	automode (all supported speeds)
F1	V.21 or Bell 103 ~#	F13	V.34 14400 bps
F3	V.23 only	F14	V.34 16800 bps
F4	V.22 or Bell 212A ~#	F15	V.34 19200 bps
F5	V.22bis only	F16	V.34 21600 bps
F6	V.32 or V.32bis 4800 bps	F17	V.34 24000 bps
F7	V.32bis 7200 bps	F18	V.34 26400 bps
F8	V.32 or V.32bis 9600 bps	F19	V.34 28800 bps
F9	V.32bis 12000 bps	F20	V.34 31200 bps
F10	V.32bis 14400 bps	F21	V.34 33600 bps

~# Dependent on the B command setting.

&F Restore factory defaults :

Options : &F0, &F1

When using the modem you may decide to change some of the S register and AT command settings. These values can be stored for future use as a User default setting using the &W command.

The &F command is used to restore the original factory default settings for AT commands and S registers (with the exception of register S80).

When used on its own the &F command temporarily restores the factory default settings until the modem is next powered up.

When used in conjunction with the &W command (AT&F&W) the User defaults are made the same as the selected factory default setting permanently. This command overwrites any changes you have made to the User default setting.

H On/off hook :

Options : H0, H1

In the same way that a telephone is said to be on-hook or off-hook, the modem has the same two states. When not in use the modem is on-hook. It automatically goes off-hook when an attempt is made to dial or an incoming call is detected with auto answer enabled.

Issuing the H0 command puts the modem on hook and consequently terminates the call. This can only take place after the escape sequence puts the modem into command mode. H0 also terminates any &T test in progress. Dropping DTR is often a more convenient method of terminating a call.

H1 takes the modem off hook in command mode. The modem returns on-hook after the period specified in register S7.

+Hn Enable/Disable RPI and DTE Speed :

Options : +H0, +H1, +H2, +H3, +H11, +H16 Default : +H0

This command enables or disables Rockwell Protocol Interface (RPI) processing and sets the DTE speed.

+H0	Disable protocol interface and video ready mode.
+H1	Enable RPI mode and set DTE speed to 19200 bps.
+H2	Enable RPI mode and set DTE speed to 38400 bps.
+H3	Enable RPI mode and set DTE speed to 57600 bps.
+H11	Enable RPI+ mode.
+H16	Enable video ready mode

When in RPI+ mode, a link is established between the modem and the WinRPI or WinRPI95 host PC software driver to allow the modem to support protocol (V.42bis/LAP-M/MNP2-5) connections with a remote modem. This command should only be used when the WinRPI or WinRPI95 driver software is installed in the PC.

I Identify :

Options : I0, I1, I2, I3, I4, I5, I6

The I command is used to request information from the modem as listed below:

I0	returns a number indicating the maximum baud rate of the modem.
I1	requests a pre-computed checksum of the modem's internal ROM.
I2	computes the checksum and compares it with the value stored in the ROM. If the check passes, the OK message is returned.
I3	requests the version number of the firmware.
I4	returns the modem's identification followed by its version number.
I5	returns the country identification for the modem.
I6	reports the modem data pump model.

&J Telephone jack control :

This command is included for completeness and performs no function within the modem.

&K DTE-to-modem flow control :

Options : &K0, &K3, &K4, &K5, &K6 Default : &K3 (&K6 fax)

Both software (XON/XOFF) and hardware (RTS/CTS) flow control are available when the modem is communicating with the local DTE.

When the modem's internal data buffer is virtually full it issues an XOFF and/or drop CTS instructing the DTE to stop sending data. When the buffer is nearly empty the modem issues an XON and/or raises CTS to resume data flow.

In software flow control (&K4) the XON/XOFF characters are filtered out of the data stream by the modem before being transmitted to the remote modem. Transparent XON/XOFF flow control (&K5) does not filter these characters. Instead the modem allows them to be transmitted to the remote DCE to instruct it to stop sending data.

&K0	disables flow control. The XON/XOFF characters are ignored and CTS is held active (HIGH) by the modem.
&K3	enables hardware RTS/CTS flow control.
&K4	enables software XON/XOFF flow control.
&K5	enables transparent XON/XOFF flow control.
&K6	enables both RTS/CTS and software XON/XOFF flow control.

\K Break control :

Options : \K0, \K1, \K2, \K3, \K4, \K5 Default : \K5

The \K command determines how the modem responds to a break received from the local DTE or the remote modem or the \B command when in on-line command mode.

The table below shows the behaviour in different scenarios.

	Break received from remote systems	Break received from DTE when transferring data	Effect of \B command on an error corrected link
\K0	Data buffers cleared. Break transmitted immediately	Enter on-line command mode	Data buffers cleared. Break transmitted immediately
\K1	Data buffers cleared. Break transmitted immediately	Data buffers cleared. Break transmitted immediately	Data buffers cleared. Break transmitted immediately
\K2	Break transmitted immediately	Enter on-line command mode	Break transmitted immediately
\K3	Break transmitted immediately	Break transmitted immediately	Break transmitted immediately
\K4	Break transmitted in sequence with data	Enter on-line command mode	Break transmitted in sequence with data
\K5	Break transmitted in sequence with data	Break transmitted in sequence with data	Break transmitted in sequence with data

-K MNP Class 10 extended services :

Options : -K0, -K1, -K2 Default : -zK0

The -K command determines whether a V.42 LAPM connection is converted to an MNP Class 10 error corrected link.

-K0	disables V.42 LAPM to MNP Class 10 conversion.
-K1	enables V.42 LAPM to MNP Class 10 conversion. It gives priority during error correction negotiation to MNP over LAPM.
-K2	Enables V.42 LAPM to MNP 10 conversion; inhibits MNP Extended Services initiation during V.42 LAPM answer mode detection phase.

L Speaker volume :

Options : L0, L1, L2, L3 Default : L2

The L command sets the in-built speaker volume. The M command controls when the speaker is enabled. Take care not to select the HIGH volume setting if using headphones connected to the rear panel socket of a voice modem.

L0	selects LOWEST speaker volume.
L1	selects LOW speaker volume.
L2	selects MEDIUM speaker volume.
L3	selects HIGH speaker volume.

%L Line signal level :

When in on-line command mode, this command returns a value which indicates the signal level received at the telephone line interface. A value of less than 20 indicates a strong signal level. A value greater than 30 indicates a weak signal level.

M Speaker control :

Options : M0, M1, M2, M3 Default : M1

The M command is used to specify when the modem's built-in speaker is active. Speaker volume is determined by the L command.

M0	disables the speaker completely so that no audible call progress is provided.
M1	enables the speaker through dialling. Upon establishing a connection the speaker is disabled.
M2	permanently enables the speaker. Should be used to give an audible indication of the call progress to assist in diagnosing any possible difficulties in establishing a connection.
M3	enables the speaker after dialling. Upon establishing a connection the speaker is disabled.

&M Asynchronous/synchronous mode selection (External modems only) :

Options : &M0, &M1, &M2, &M3

A subset of the &Q command. Provided for compatibility purposes only.

+MS Modulation select :

Options : [modulation], [automode], [min. speed], [max. speed]

The +MS= command may be used to set the line speed for V.34 modems.

The command selects the modulation, enables or disables automode, and optionally specifies the lowest and highest connection rates. The command format to select a line speed is:

AT+MS=[modulation],[automode],[min. speed],[max. speed] <Return>

To view the currently selected parameters type AT+MS? <Return>

To view the supported options for each parameter type AT+MS=? <Return>

The following sections define the parameters and accepted options for the +MS= command.

Modulation selection
A decimal number which specifies the preferred modulation (if automode is enabled) or the fixed modulation (if automode is disabled) used in a connection.

0	= V.21 (300 bps)
1	= V.22 (1200 bps)
2	= V.22bis (1200 or 2400 bps)
3	= V.23 (1200/75 or 75/1200 bps)
9	= V.32 (4800 or 9600 bps)
10	= V.32bis (4800, 7200, 9600, 12000 or 14400 bps)
11	= V.34 (2400, 4800, 7200, 9600, 12000, 14400, 16800, 19200, 21600, 24000, 26400, 28800, 31200 or 33600 bps)
12	= V.90 (28000, 29333, 30667, 33333, 34667, 37333, 38667, 41333, 42667, 45333, 46667, 49333, 50667, 53333, 54667, 56000 bps) Default setting (V.90)
56	= K56flex (56000, 54000, 52000, 50000, 48000, 46000, 44000, 42000, 40000, 38000, 36000, 34000, 32000). Default setting (K56flex)
64	= Bell 103 (300 bps)
69	= Bell 212 (1200 bps)

Automode
Automatic line speed selection or "automode" is a feature that lets the modem automatically determine the type of incoming carrier signal. It operates in both dialling and answering modes when the modem is attempting to establish a connection. This parameter of the +MS command is used to either enable or disable automode as follows:

0	= automode disabled, fixed modulation.
1	= automode enabled. This is the default setting.

To create a fixed mode of operation set the minimum and maximum line speeds to be the same. For example, to set the modem for V.32bis 12000 bps fixed mode, type:

AT+MS = 9,0,12000,12000 <Return>

Minimum and maximum line speeds
You use these two parameters to specify the lowest and highest line speeds at which the modem may establish a connection. The number you enter at these two parameters reflects the bps rate, i.e. 14400 sets a rate of 14400 bps.

Setting the minimum and maximum line speed may constrain the range of modulations available, even with automode enabled.

The default option for minimum speed is 300 (i.e. 300 bps)

The default option for maximum speed is 56000 (i.e. 56000 bps)

Example
AT+MS = 11,1,1200,24000 <Return>

selects V.34 as the preferred modulation with automode enabled. The minimum permitted line speed is 1200 bps and the maximum is 24000 bps. Parameters that are not entered in the command line, by either typing the comma only or <Return>, remain at their current setting (not necessarily the default setting).