Hayes Modem: AT Command Listing

1.1 AT Command Listing

Each step in the evolution of Hayes modems has added to a feature set that has enhanced the definition of the Hayes standard.

Please select a command:

A	B	C	D	E	F	H	I	L	M
N	O	S	T	V	X	Y	Z	&A	&B
&C	&D	&F	&G	&J	&K	&L	&O	&Q	&R
&S	&T	&U	&V	&W	&X	&Y	&Z

A - Answer Command

The A command instructs the modem to go off hook and respond to an incoming call, then handshake with the remote modem. When the modem returns the RING result code, issue ATA<CR>. The modem will send an answer carrier signal to the originating modem and wait for an originate carrier signal. When the modem receives the carrier from the originating modem, the modems go through a`handshaking' process then go on-line. The modem returns the CONNECT XXXXX or CARRIER XXXXX result code (see "Result Code Listing" in this chapter). If no carrier signal is received within the time specified in register S7, the modem hangs up, returns the NO CARRIER result code, and enters the command state. By using the &An command, the modem can be forced to answer in the originate mode.

B - Select Communication Standard

The B command is used to specify the desired communications standard setting at a particular modem line speed. Because options can select between groups of options, more than one combination of communication standard and speed can be selected. For example, you can issue B1 and B16; both will be in effect because they do not reference the same line speed. However, choosing B1 then B5 selects B5, and replaces B1 as the standard for 1200 bps communications. The most recent selection chosen from any given group will be in effect for that parameter group.

Group 1
Command     Description
B or B0     V.22 when line speed is at 1200 bps.
B1          U. S. Domestic industry standard 212A when line speed is
            at 1200 bps.
B2          V.23 R1200/T75 bps Auto Speed Buffering (ASB) when
            line speed is at T1200/R1200 bps.
B3          V.23 T1200/R75 bps Auto Speed Buffering (ASB) when
            line speed is at T1200/R1200 bps.
B4          V.23 T1200/R75 bps split speed when line speed is at
            T1200/R75 bps.
B5          V.23 1200 bps half duplex when line speed is at
            T1200/R1200 bps.

Group 2
Command     Description
B10         V.23 R1200/T75 bps split speed when line speed is at
            R1200/T75 bps.
B11         V.23 R600/T75 bps split speed when line speed is at
            R600/T75 bps.

Group 3
Command     Description
B15         V.21 when line speed is 110/300 bps.
B16         U. S. Domestic industry standard 103 when line speed is
            at 110/300 bps.

Group 4
Command     Description
B20         V.23 R600/T75 bps ASB when line speed is T600/R600 bps.
B21         V.23 T600/R75 bps ASB when line speed is T600/R600 bps.
B22         V.23 T600/R75 bps split speed when line speed is
            T600/R75 bps.
B23         V.23 600, half duplex when line speed is 600 bps.

Group 5
Command Description
B30 V.22bis when line speed is 2400 bps.

Group 6
Command     Description
B41         V.32 full duplex when line speed is 4800 bps.
B42         Express(TM) 96* when line speed is 4800 bps.

* Express 96 - a Hayes proprietary protocol that simulates full-duplex 9600 bps operation (formerly known as Hayes fast-turnaround "Ping-Pong" protocol).

Group 7
Command Description
B50 V.29 HDX when line speed is 7200 bps.

Group 8
Command     Description
B60         V.32 full duplex when line speed is 9600 bps.
B61         Express 96 when line speed is 9600 bps.
B63         V.29 half duplex when line speed is 9600 bps.

C - Carrier Control Selection

The C command is used by some Hayes modems, such as Smartmodem(TM) 1200, to control the transmit carrier. In these instances, C0 instructs the modem to not send carrier (i.e., puts modem in a receive-only mode). High-speed modems (those capable of speeds greater than 1200 bps) accept C1 without error in order to assure backward compatibility with communications software that issues C1. However, these modems do not support C0.

C0 Transmit carrier always off (not supported in high-speed modems)
C1 Normal transmit carrier switching

D - Dial Command

The D command places the modem in originate mode; it then functions as an auto-dialer. Whether the command is issued on a line by itself, or followed immediately by the telephone number, it must be preceded by the AT prefix and terminated with a <CR>. (Note that <CR> is the notation used throughout this reference to represent the carriage return, enter, or return function on your keyboard.)

The dial string is a combination of dial digits and dial modifiers. If the modem is off hook, it will neither initially wait nor attempt to detect dial tone before proceeding. The D command is not valid when the modem is on-line or if either &Q2 or &Q3 is in effect.

Parentheses and hyphens in a dial string are ignored by the auto-dialer, but are counted as characters in the command buffer. The command buffer for most Hayes Smartmodem products can contain as many as 40 characters. Hayes V-series (TM) products can hold as many as 255 characters in their command buffers. Check your user documentation to determine the maximum number of characters supportted in your modem's command buffer.

Result Codes Description

BUSY             If X3 or X4 are selected or W dial modifier is used and
                 busy is detected.
NO DIALTONE      If X2 or X4 are selected and 1 second of dial tone is
                 not detected; in response to a W dial modifier if dial
                 tone is not detected within the time specified by S7.
ERROR            If the S=n dial modifier is processed and the n value
                 is out of range (refer to the S dial modifier in this
                 section) or if the total number of characters in the
                 command line plus the stored dial string exceeds the
                 command buffer limit.
NO ANSWER        If @ dial modifier is used and then no signal is
                 detected for at least five continuous seconds before
                 the time specified by S7.
OK               If aborted by DTR ON-to-OFF whenever certain
                 combinations of &D and &Q are in effect. Refer to
                 the &D command in this chapter for details; if the
                 semicolon (;) dial modifier is processed in the dial
                 string; if aborted by a character from the DTE during
                 the dialing process.

Dial Modifiers

Dial modifiers can be combined with the dial (D) command to perform a series of operations within a single command line. For example, ATDT9W5552368!@#71234; <CR> instructs the modem to use tone dialing (T) to access a number outside a PBX (9), wait for dial tone (W), dial the number 5552368, enter a timed break recall (!), wait for quiet answer (@), and issue the PBX transfer code (#7) before dialing extension number 1234, then return to the command state; before initiating the handshake.

0-9 A B C D # * - Digits/Characters for Dialing

The digits/characters 0-9 A B C D # * are numbers and characters the modem can dial. The characters A B C D # * represent specific tone pairs and therefore can be used only when tone dialing is selected; these symbols are ignored when pulse dialing is used.

P - Pulse Dialing Method

The P dial modifier selects the pulse method of dialing. The P modifier can be issued with the dial command, or alone, to indicate the method used for subsequent dialings. The factory-set method is pulse. Once this method is selected, it is used until the other is chosen, or the modem is reset.

T - Tone Dialing Method

The T dial modifier selects the tone method of dialing. The T modifier can be issued with the dial command, or alone, to indicate the method used for subsequent dialings. Once this method is selected, it is used until the other is chosen, or the modem is reset, reinstating pulse dialing.

W - Wait for Second Dial Tone

The W dial modifier instructs the modem to wait for dial tone before proceeding. If dial tone detection is not completed within the preset time limit, the modem hangs up and returns the NO DIALTONE result code. Some PBXs do not return a secondary proceed indication (second dial tone). The W dial modifier is not effective in such systems and should not be used.

, - Delay Processing of Next Character

The comma (,) dial modifier in a dial string causes the modem to pause before processing the next character or symbol in the command line. The duration of the pause is determined by the value held in register S8. The comma is frequently inserted after the 9 (digit generally used to gain outside access from a PBX) to allow sufficient time for the dial tone to occur before the modem dials the telephone number.

@ - Wait for Quiet Answer

The @ dial modifier instructs the modem to listen for five seconds silence before continuing. The number of seconds the modem waits for silence is determined by the value held in S7. This modifier is useful when dialing telephone systems that produce no dial tone.

If a five-second silence has not been detected within the period set in S7, the modem hangs up and returns the NO ANSWER result code. If it detects the five seconds of silence, the modem processes the remaining characters in the dial string.

Note that the modem does not listen for silence until it first detects dial tone and some other signal, such as a ringing signal, that lasts longer than 210 milliseconds. For example, to dial 5552368, wait for a quiet answer, then dial a security code 85939, wait for a second dial tone, and dial extension 423 you would issue the following command: ATDT 5552368 @ 85939 W 423 <CR>.

! - Timed Break Recall (Hookflash)

The ! dial modifier issues a timed break recall signal, which causes the modem to hang up briefly, then reconnect. This feature can be used to access such PBX features as call transfer.

; - Return to Command State after Dialing

The semicolon (;) dial modifier, used only at the end of a command line (just before the <CR>), instructs the modem to return to the command state immediately after dialing, without breaking the connection.

The ; is useful when calling an electronic service, such as that offered by a bank, that permits you to use tones to transmit numbers once a connection has been established. The modem can send tones even if your telephone cannot. The example below illustrates the use of the semicolon modifier in communications with an electronic banking service.

ATDP 5552368; <CR>      Dials bank using pulse method.
OK                      Command executed, but keeps the modem in command
                        state (no carrier handshake takes place).
ATDT 4768; <CR>         Sends an ID code via tones and maintains modem
                        in command state.
OK                      Modem in command state; command executed.

In this example, the ; differs from the +++ in that the Hayes improved escape sequence with guard time places the modem in the command state only when two modems have completed a handshake. The semicolon keeps the modem in command state; no CONNECT XXXXX result code is displayed.

DS=n - Dialing a Stored Telephone Number

A stored number can be dialed from an asynchronous terminal by following the dial (D) command with the S modifier, an equal sign, and the location of the stored number (see &Zn=x command at the end of this section). The format of the modifier is S=n, where n is location 0-3. If ATDS=2<CR> were issued, for example, the modem would dial the string stored in memory location 3 of its "telephone book."

R - Originate a Call in Answer Mode

The dial modifier R (Reverse mode) enables the modem to dial an originate only modem by placing a call in answer mode. This modifier must be entered at the end of the dialing (D) command string, before the <CR>. The R modifier directs the modem to act as if it had been sent an A command in that part of the command string.

E - Command State Character Echo Selection

The E command determines whether characters are echoed to the DTE from the modem when it is command state. Some computers and terminals do not send the characters you type to the screen; they only transmit them to the remote system through the serial port. In this case, if Command State Character Echo were not enabled by the modem, you would be unable to see what you type. If the DTE does echo the characters you type in command state, and this function is enabled in the modem, each character typed will appear twice.

E0 Command state character echo disabled.
E1 Command state character echo enabled.

F - On-line State Character Echo Selection

The F command is used by some Hayes modems, such as Smartmodem 1200, to determine whether characters are echoed to the DTE from the modem when it is in the on-line state. High-speed Hayes modems do not support the F0 option. However, because the F command may be issued by older communications software, F1 is supported to assure backwards compatibility.

F0      On-line character echo enabled (where not supported, ERROR
        result code is returned).
F1      On-line character echo disabled.

H - Hook Command Options

The H command provides control over the line relay. Its most common use is with the H0 option to initiate the Hangup Process and place the modem on hook. H1 takes the modem off hook.

H0     Execute the Hangup process if in the "on-line" command state or
       the local analog loopback and analog loopback self-test
       conditions.
H1     Go off hook; do not execute the Handshake Process.
H2     Operate line relay only (applies to certain Smartmodem 1200
       products).

I - Internal Memory Tests

The various forms of the I command instruct the modem to query its memory for information about itself. The results of these tests are frequently used by programmers to determine compatibility with software. Because these commands request information about the modem's firmware, they are not run when a connection has been established with a remote modem.

I0 - Display Product Code

Result Codes     Description
300              Smartmodem 300.
120              Smartmodem 1200, Smartmodem 1200B, Smartmodem 1200C,
                 Smartmodem 1200A.
240              Smartmodem 2400, Smartmodem 2400B, Smartmodem 2400P,
                 Smartmodem 2400Q, Smartmodem 2400M, V-series Smartmodem
                 2400, V-series Smartmodem 2400B, V-series Smartmodem
                 2400 Quad, V-series Smartmodem 2400M, Smartmodem OPTIMA
                 (TM) 24, Smartmodem OPTIMA 24 + FAX96,
                 ACCURA (TM) 2400 EC/FAX96.
960              Smartmodem 9600, V-series Smartmodem 9600, V-series
                 Smartmodem 9600B, V-series ULTRA (TM) Smartmodem 2400,
                 V-series ULTRA Smartmodem 9600, V-series ULTRA 24 with
                 Express 96, Smartmodem OPTIMA 9600, Smartmodem
                 OPTIMA 96 + FAX96, ACCURA 9600 EC/FAX96.
14400            V-series ULTRA Smartmodem 14400, Smartmodem OPTIMA 144,
                 Smartmodem OPTIMA 144 + FAX144, ACCURA 14400 EC/FAX144.

I1- Display ROM Checksum

The I1 command instructs the modem to calculate the value of the ROM checksum. The response is a number, the sum of all of the bytes in ROM. I2 - Perform ROM Checksum

This command instructs the modem to verify the ROM checksum. Depending on whether the ROM checksum has been found to be correct, the modem produces text that resembles a result code. The modem memory test compares the ROM checksum and tests it against the correct sum, also stored in ROM. Rather than returning a numeric value as in I1, the I2 command generates a result code. When the checksum is valid, the response is: OK. When the ROM checksum fails, the modem responds with ERROR. I4 - Identify Product Features

Since the following tables identify features for Hayes modem products, the values included here and the number of strings are subject to change and expansion. The maximum length per string is 40 characters.

The I4 text is displayed in the following form:

     a097800C204C264
     bF60410000
     r1031111111010000
     r3000111010000000

surrounded by additional <CR> and <LF> characters as are required by the V command option in effect. According to convention, all <CR> and <LF> characters are defined by S3 and S4, respectively. The meanings of the a, b, r1, and r3 strings currently defined are described below.

I4 "a" String
The first string, the a-string, is composed of the ASCII character "a" followed by a series of hexadecimal characters (D1-D16 in this example). The bit map for each byte is defined below.

a D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14 D15 D16 D17 D18....

D1, D2     Reserved
D3         Bit 3: Indicates modem based on SM1200FE commands
           Bit 2: Indicates modem based on SM2400 commands
           Bit 1: Indicates that modem supports &J commands
           Bit 0: Indicates that modem supports &L commands
D4         Bit 3: Indicates that modem supports AutoSync (&Q4)
D5         Bit 3: Plug-in board modem product
           Bit 2: Standalone modem product
           Bit 1: Supports &H0 through &H4
           Bit 0: Supports &I0 through &I4
D6         Bit 3: Reserved
           Bit 2: Supports M4 command
           Bit 1: Supports 32-bit FCS (frame check sequence            for AutoSync)
           Bit 0: Supports AutoSync II
D7         Bit 3: Supports V.22 at 1200 bps (B0)
           Bit 2: Supports 212A (B1)
           Bit 1: Supports ASB in V.23 75 bps xmt/1200 bps rcv (B2)
           Bit 0: Supports ASB in V.23 1200 bps xmt/75rcv (B3)
D8         Bit 3: Supports V.23 1200 bps xmt/75 bps rcv (B4)
           Bit 2: Supports V.23 1200 half duplex (B5)
           Bit 1: Supports V.23 75 bps xmt/1200 bps rcv (B10)
           Bit 0: Supports V.23 75 bps xmt/600 bps rcv (B11)
D9         Bit 3: Supports V.21 100/300 bps (B15)
           Bit 2: Supports ASB in V.23 75 bps xmt/600 bps rcv (B20)
           Bit 1: Supports ASB in V.23 600 bps xmt/75 bps rcv (B21)
           Bit 0: Supports V.23 600 bps xmt/75 bps rcv (B22)
D10        Bit 3: Supports V.23 600 bps half-duplex (B23)
           Bit 2: Supports V.22bis at 2400 bps (B30)
           Bit 1: Supports V.27ter at 2400 bps (B31)
           Bit 0: Supports V.27ter at 4800 bps (B40)
D11        Bit 3: Supports V.32 full duplex at 4800 bps (B41)
           Bit 2: Supports Express 96 at 4800 bps (B42)
           Bit 1: Reserved
           Bit 0: Supports V.29 half duplex at 4800 bps (B44)
D12        Bit 3: Supports V.29 half duplex at 7200 bps (B50)
           Bit 2: Supports V.32 full duplex at 9600 bps (B60)
           Bit 1: Supports Express 96 at 9600 bps (B61)
           Bit 0: Reserved
D13        Bit 3: Supports V.29 half duplex at 9600 bps (B63)
           Bit 2: Supports 103 110/300 bps (B16)
           Bit 1: Supports V.32bis (7200/12000/14400 bps)
           Bit 0: Reserved

D1, D2     Reserved
D14        0: Reserved
           1: Personal Modem 1200
           2: Personal Modem 2400
           3: Personal Modem 1200 Plus
           4: Personal Modem 2400 Plus
           5: Pocket Edition
D15        Bit 3: Reserved
           Bit 2: Supports $ dial modifier and NO DIALTONE result code.
           Bit 1: Supports S95 Bit 5 for COMPRESSION: result code
           Bit 0: Supports S95 Bit 4 for AUTOSTREAM: result code
D16        Bit 3: Supports S95 Bit 3 PROTOCOL: result code
           Bit 2: Supports S95 Bit 2 CARRIER result code
           Bit 1: Supports S95 Bit 1 CONNECT/ARQ result code
           Bit 0: Supports S95 Bit 0 CONNECT XXXX (for DCE rate)

The second string, the b-string, is composed of the ASCII character "b" followed by a series of hexadecimal characters (D1-D9). The bit map for each character is defined as follows:

b D1 D2 D3 D4 D5 D6 D7 D8 D9....

D1 Bit 3: V.42 Alternate Protocol Supported

Bit 2: V.42 LAPM Protocol Supported

Bit 1: X.25 Protocol Supported

Bit 0: LAPB (Point-to-point error control) protocol supported

D2 Bit 3: Reserved (should be set to zero)

Bit 2 MNP (TM) Class 5 supported

Bit 1: V.42bis supported

Bit 0: Compression through the X.25 network supported

D3/D4 These combine to indicate the number of AutoStream

Type A channels which are supported. The formula

(D3*16 + D4) is used. Zero means AutoStream is not supported

D5 Bit 3: Reserved

Bit 2: Reserved

Bit 1: Adjustable startup (ASU) is supported

Bit 0: Negotiates adjustable startup

D6 Bit 3: &K5 not supported

Bit 2: &K5 supported

Bit 1: Unidirectional flow control

Bit 0: S105 N104 parameter supported

These ID strings allow software to determine the available speeds that may be used to send AT commands. The r1-string contains a bit map that indicates at which DTE rates the autobaud process is supported.

The presence of the r2-string in the I4 result infers that S87 is supported and is required for autobauding at the higher speeds. To autobaud at one of the speeds indicated in the r2-string requires that S87 be set to match that speed.

The r3-string is issued if synchronous DTE speeds are supported. The map indicates which DTE rates are supported in synchronous modes. Each r-string begins with the lower case letter "r" and may be followed by as many as 39 additional characters, not counting <CR><LF>'s that will be used to separate them from other strings. Those 39 additional characters are limited to the ASCII-HEX alphabet 0-9 and A-F.

After the two lead-in characters (i.e., r<n>), all subsequent characters contain the DTE rate maps. All maps have the same mapping for convenience to software. (Refer to the following chart.) Not all bit assignments are possible: for example, the split speeds have no meaning in the r3 synchronous map and are always filled with zeros.

In r1, if the bit is filled with a 1, the corresponding DTE rate is supported for sending AT commands to the device. A zero indicates that DTE rate is not supported for AT commands.

In the r3 map, the bits simply indicate which DTE rates are supported for synchronous operation on-line. This does not indicate, however, the supported rates for synchronous V.25bis commands.

Split speeds if available are marked in the r1 string only when the appropriate B command option has been selected. Future expansion of these strings may include new speeds that are not in strict ascending order.

DTE Rate Bit Map for r1, r2 and r3 Strings

Character    Bit #       DTE Rate
------------------------------------------------------------------------
3: 1       bit 0       45.45 bps
     2       bit 1       50
     4       bit 2       75
     8       bit 3       75/600 (xmt is 75, rcv is 600)
4: 1       bit 4       75/1200
     2       bit 5       110
     4       bit 6       134.5
     8       bit 7       50
5: 1       bit 8       300
     2       bit 9       450
     4       bit 10      600
     8       bit 11      600/75
6: 1       bit 12      1200
     2       bit 13      1200/75
     4       bit 14      1800
     8       bit 15      2000
7: 1       bit 16      2400
     2       bit 17      3000
     4       bit 18      3600
     8       bit 19      4200
8: 1       bit 20      4800
     2       bit 21      5400
     4       bit 22      6000
     8       bit 23      6600
9: 1       bit 24      7200
     2       bit 25      7800
     4       bit 26      8400
     8       bit 27      9000
10: 1       bit 28      9600
     2       bit 29      12000
     4       bit 30      14400
     8       bit 31      16800
11: 1       bit 32      19200
     2       bit 33      21600
     4       bit 34      24000
     8       bit 35      26400
12: 1       bit 36      28800
     2       bit 37      31200
     4       bit 38      33600
     8       bit 39      36000
13: 1       bit 40      38400
     2       bit 41      43200
     4       bit 42      48000
     8       bit 43      52800
14: 1       bit 44      56000
     2       bit 45      57600
     4       bit 46      62400
     8       bit 47      64000
15: 1       bit 48      67200
     2       bit 49      72000
     4       bit 50      76800
     8       bit 51      81600
16: 1       bit 52      86400
     2       bit 53      91200
     4       bit 54      96000
     8       bit 55      100800
17: 1       bit 56      105600
     2       bit 57      110400
     4       bit 58      115200
     8       bit 59      reserved ("0")

L - Speaker Volume Level Selection

The L command setting determines the volume level of the speaker, when supported by the modem. Some modems use the speaker of the computer in which they are installed. In this case, where supported, the L command adjusts the speaker volume as indicated in the options below for the duration of the communications session.

L0, L1     Low speaker volume
L2         Medium speaker volume
L3         High speaker volume

M - Speaker On/Off Selection

The M command setting determines whether the speaker function of the modem is on or off. Some modems use the speaker of the computer in which they are installed. In this case, where supported, the M command turns the speaker on and off as indicated in the options below for the duration of the communications session.

M0     Speaker always off.
M1     Speaker on until carrier detected.
M2     Speaker always on; stays on after carrier is detected.
M3     Speaker off as digits are dialed, but on during ringback and on
       until carrier signal is detected.

N - Negotiation of Handshake Options

The N command selects whether or not the local modem performs a negotiated handshake with a remote modem when the communications speeds of the two modems are different. The options for this command are useful when a particular speed and communication standard are required. Both symmetrical and asymmetrical protocols can be selected. Note that the options supported by this command vary significantly between country-specific implementations.

N0 When originating or answering, handshake only at the
communication standard specified by S37 and B command.

N1     When originating, begin handshake at the communication standard
       specified by the B command and S37. During handshake fallback to
       a lower speed may occur. When answering, negotiate according to
       the following sequence of communication standards: V.32,
       Express 96, V.22bis, V.22/212A, and V.21/103.

N2     When originating, begin handshake at the communication standard
       specified by the B command and S37. During handshake fallback
       to a lower speed may occur. When answering, negotiate according
       to the following sequence of communication standards: V.32,
       Express 96, V.22bis, V.22/212A, V.23, and V.21/103.

N3     When originating, handshake only at the communication standard
       specified by S37 and B command. When answering, negotiate
       according to the following sequence of communication standards:
       V.32, Express 96, V.22bis, V.22/212A, and V.21/103.

N4     When originating, handshake only at the communication standard
       specified by S37 and B command. When answering, negotiate
       according to the following sequence of communication standards:
       V.32, Express 96, V.22bis, V.22/212A, V.23, and V.21/103.

N5     When originating, begin handshake at the communication standard
       specified by B command and S37. During handshake fallback to a
       lower speed may occur. When answering, handshake only at the
       communication standard specified by S37 and B.

O - On-Line Command

If the modem is in the on-line command state, then the O0 command causes it to go to the on-line state of the previously established connection. If the O1 command is issued (modems supporting 2400 bps and higher), the modem goes to on-line state and retrains its adaptive equalizer. If the O3 command is issued (modems supporting V.32bis), the modem goes to on-line state and initiates the CCITT V.32bis renegotiation sequence.

If the modem is off hook in the idle state, then O0 and O1 (modems supporting 2400 bps and higher) cause it to go to the handshaking state. Originate or answer mode is determined from the last D or A command or R dial modifier that was selected. If the modem is on-hook, idle, or if the modem is in a test condition, a command execution error results. Note that O1 serves a different purpose in lower speed modems (e.g., Smartmodem 1200 and Smartmodem 300).

P - Select Pulse Dialing Method

The P command instructs the modem to use pulse dialing. Dialed digits will be pulse dialed until a T command or dial modifier is received. This command is also discussed under "Dial Modifiers," in conjunction with the D command.

Q - Result Code Display Options

The Q command controls whether the result codes generated by the modem are displayed to the attached DTE. Some software does not function properly when modem responses are returned.

Q0     Result codes enabled
Q1     Result codes disabled
Q2     Disables the RING result code. In answer mode, also disables
       CONNECT and NO CARRIER result codes.

Sr - Addresses An S-register

The Sr command points to a specific S-register. Subsequent commands, such as ? and =, may read or write to the selected register. Note that S0 is the factory-set pointer for this command, and that the S-address is not stored in a stored profile. Thus, the &F, Z0, and Z1 commands will select S0 and possibly affect subsequent ? and = commands unless they are preceded by an Sr command. command points to a specific S-register. Subsequent commands, such as ? and =, may read or write to the selected register. Note that S0 is the factory-set pointer for this command, and that the S-address is not stored in a stored profile.

Sr? - Read An S-register

The content of S-register r are sent to the DTE as three decimal digits. This informational text response is formatted with <CR><LF> as determined by the V command currently in effect. If no n (suffix) is present, the last register selection is assumed. (Refer to the Sr command.) On power up, the factory-set selection is 0. Note that ? is interpreted by the modem as Sr?.

T - Select Tone Dialing Method

The T command instructs the modem to send DTMF tones while dialing. Dialed digits will be tone dialed until a P command or dial modifier is received. This command is also discussed under "Dial Modifiers," in conjunction with the D command.

V - Result Code Format Options

The V command determines whether result codes (including call progress and negotiation progress result codes) are displayed as numbers or words.

V0 Result codes displayed as numbers
V1 Result codes displayed as words

W - Negotiation Progress Message Selection

The W command works in conjunction with S95 (where supported) to determine which result codes will be used to describe the type of connection and protocol, etc., that resulted from handshaking and negotiation.

The W command supports extended result codes in addition to the CONNECT result code. When the modem is operated in error-control mode (&Q5 is in effect), the W command and S95 together allow the user to select these additional result codes:

Any result codes enabled by the W command and S95 will be generated in the order indicated above. If AutoStream is not being used, no AUTOSTREAM result code is returned. Result codes not enabled when the W command option is in effect may be turned on by setting certain bits in S95. The W command options below are available when S95 is configured for any setting other than the factory-setting of 0.

W0     CONNECT result code reports DTE speed, and if S95=0, then disable
       all extended result codes.
W1     CONNECT result code reports DTE speed, and if S95=0, then enable
       the CARRIER and PROTOCOL extended result codes.
W2     CONNECT result code reports DCE speed, and if S95=0, then disable
       all extended result codes.

Refer to the S95 bit map description in the next section. Note that selecting W0 and setting S95=12 is the same as selecting W1; and that selecting W0 and setting S95=1 is the same as selecting W2. S95 cannot be configured to force W2 to report DTE speed in the CONNECT result code; there is no setting of S95 that will force W1 not to produce the CARRIER and PROTOCOL result codes. S95 extends the functionality of the W command. The W command with S95=0 (factory setting) maintains backwards compatibility with previous Hayes Products. However, selecting W0 and setting S95 as required allows you to tailor result code characteristics to your own requirements.

X - Call Progress Options

The X command enables tone detection options used in the dialing process. As these functions are enabled and disabled, the modem's result code reporting is also affected. For this reason, this command is frequently used to control the modem's range of responses; however, its primary function is that of controlling the modem's call response capabilities. Some call progress options are not available in certain countries due to PTT regulations. Refer to the user documentation supplied with your modem for applicable X commands and result codes. Result code definitions are provided in the next section.

X0     Busy and dial tone detection are disabled. Only result codes 0-4
       are enabled. Only the CONNECT result code is permitted, but with
       no indication of the telephone line speed. This setting overrides
       any other result code selections made with the W command and S95.

X1     Busy and dial tone detection are disabled. Result codes 0-5 are
       enabled and line speed reporting with CONNECT XXXX messages. W
       command options and S95 are enabled.

X2     Busy detection is disabled. Dial tone detection is enabled.
       Result codes 0-6 are enabled and line speed reporting with
       CONNECT XXXX messages. W command options and S95 are enabled.

X3     Busy detection is enabled. Dial tone detection is disabled.
       Result codes 0-5 and 7 are enabled and line speed reporting
       with CONNECT XXXX messages. W command options and S95 are
       enabled.

X4     Busy and dial tone detection are enabled. Result codes 0-7
       are enabled and line speed reporting with CONNECT XXXX messages.
       W command options and S95 enabled.

The @ and W dial modifier result codes are not affected by the X command. The @ dial modifier enables result codes 8 (NO ANSWER) and 7 (BUSY) each time it occurs in the dial string. The W dial modifier enables result codes 6 (NO DIALTONE) and 7 (BUSY) each time it occurs in the dial string.

Y - Long Space Disconnect Options

The Y command determines if the modem will disconnect a call upon receiving a long space (1.6 sec break) signal from the distant end. If Y1 is selected, the modem will send a 4-second break (space) before going on hook when an H0 command is issued or, if &D2 is selected, when DTR goes off. Refer also to register S82 for more information.
Y0 Disable long space disconnect
Y1 Enable long space disconnect

Z - Soft Reset Command

The modem can be reset by issuing the Z command. The command tells the modem to go on hook and restore the selected stored profile. Any non-storable parameters previously set by commands are returned to their factory settings. The modem aborts execution of all commands following the Z command on the same command line. Subsequent commands on the same line are ignored. Refer to the &W command for description of which modem parameters are included in a stored profile. Z0 recalls stored user profile 0, stored with &W0; Z1 recalls stored user profile 1, stored with &W1.

Z0 Recall stored profile 0
Z1 Recall stored profile 1

&A - Select Originate or Answer Role for Auto-Answer Mode

The &A command determines whether the modem will attempt to connect as the originating or answering modem when auto-answering calls.

&A0 Connect as answering modem when auto-answering
&A1 Connect as originating modem when auto-answering

Notes:

S0 must be set to a non-zero value to enable AutoAnswering.
The &An setting only affects the mode of AutoAnswered calls. The &An setting does not affect the mode or behavior of ATA, ATD, ATDR, DTR-Dial, MI/MIC, KDS, or Power-Up initiated connections.
The &A or &A0 setting is exactly equivalent to traditional Auto-Answered connections. It is controlled by register S0. Answer Tone is issued if the modulation standard requires it, and handshaking proceeds in the answer direction.
When &A1 has been selected and S0 is non-zero and the modem AutoAnswers an incoming call, the modem performs the Answer process and then the Handshake process with the exception that the Handshake process is performed in the Originate mode and Answer Tone is not issued.
If parameter values greater than 1 are attempted, an ERROR result code is issued, and no change is made to the &An setting.

&B - V.32/V.32bis Auto Retrain Options

The &B command is used to enable and disable auto retrain in V.32/V.32bis mode. During a V.32 or a V.32bis connection, the modem continually monitors line quality. The &B command determines whether the modem ignores a line quality problem or attempts to correct the situation by retraining. The selection made with this command affects V.32/V.32bis connections only.

&B and &B0 Disable V.32/V.32bis Auto Retrain
&B1 Enable V.32/V.32bis Auto Retrain

&C - Data Carrier Detect Options

The &C command determines how the state of the DCD lead relates to the carrier from the distant end. The command will take effect immediately when issued. The behavior patterns for DCD depend on the specific &C and &Q commands in effect. Also, DCD patterns depend on whether on-line operation is half or full duplex. Finally, if &Q5 is in effect, DCD behavior depends on whether S10=255 or S10<255. DCD circuit operation is according to the descriptions below.

DCD Behaviors for Full-Duplex             DCD Behaviors for Half-Duplex
Operation                                 Operation
------------------------------------------------------------------------
      &C0   &C1   &C2                          &C0   &C1   &C2
&QO   A     B     D                       &Q1   E     C     C
&Q1   B     B     B                       &Q2   E     C     C
&Q2   B     B     B                       &Q3   E     C     C
&Q3   B     B     B                       &Q4   E     C     C
&Q4   B     B     B                       &Q5   A     E     A
&Q5   A     E     A                       &Q5   A     C     F
&Q6   A     B     D                       S10=255
&Q5   A     B     D
S10=255

See Legends that follow for explanation of table entries A-F.

Table Legend:
A The DCD circuit is ON at all times.

B DCD=0 in idle; DCD tracks carrier in On-Line State with S9

      The DCD circuit is OFF while the connection attempt is being made.
      It goes ON immediately after the CONNECT result code is issued,
      and goes OFF immediately after loss of remote carrier. If the
      remote carrier is restored and the S9 (carrier detect response
      time) delay is completed before the S10 (lost carrier to hang-up)
      delay expires, then hang-up is avoided and the DCD circuit goes ON
      again as the modem goes on-line. Otherwise, DCD remains OFF
      during the hang-up process prior to the result code message. If
      S10=255, hangup will not occur unless initiated by the DTE.

C DCD=0 in idle; DCD tracks carrier in On-Line State without S9

      The DCD circuit is OFF when the modem is idle. It goes ON
      immediately after the CONNECT result code is issued, and goes OFF
      immediately after loss of remote carrier. If the remote carrier is
      restored, then DCD will go ON regardless of the S9 value
      in effect.

D DCD=1 in idle; DCD tracks in On-Line with S

      The DCD circuit is normally ON when the modem is idle, and it is
      ON while the remote carrier is present and the modem is on-line.
      The signal goes OFF immediately after loss of remote carrier. If
      the remote carrier is restored, then DCD will go ON again
      regardless of S9. If the Hangup Process is initiated by the DTE
      using DTR or issuing ATH<CR> from the on-line state, then DCD will
      return ON just prior to the modem issuing the OK result code. If
      S10<255 (lost carrier to hang-up delay) and a timeout equal to S10
      expires before the remote carrier is restored, then the hang-up
      process begins during which DCD=0.

      DCD will return ON again just prior to the issue of the NO CARRIER
      result code. If the remote carrier is restored and the S9 delay is
      completed before the S10 delay expires; then the modem does not hangup,
      and DCD will go ON again when the modem returns on-line.

E DCD=0 in idle; DCD=1 in On-Line State (no tracking)

      The DCD circuit is OFF when the modem is idle in the command
      state. DCD goes ON immediately after the CONNECT result code is
      issued, and it goes OFF when the modem begins the hangup process.
      DCD does not track the presence of remote carrier energy.

F DCD=1 in idle; DCD tracks in On-Line without S9

      This behavior pattern is associated only with (&C2, &Q5, S10=255,
      half duplex), and it only occurs at 4800 and 9600 bps when
      Express 96 is in effect (Hayes proprietary V.32 half-duplex
      operation (Ping Pong)). The DCD circuit is normally ON when the
      modem is operating in half duplex and idle in the command state,
      and it is ON while the remote carrier is present in the on-line
      state. It goes OFF approximately 3 seconds after loss of remote
      carrier. If the remote carrier is restored, then DCD will go ON
      again (regardless of S9). If the hangup process is initiated by
      the DTE using DTR or escaping to command state and issuing ATH<CR>
      when on-line, DCD will return ON just prior to the modem issuing
      the OK result code. The modem will not begin the hangup process
      if S10=255.

&D - Data Terminal Ready Options

The &D command affects how the modem will respond to the state of the DTR signal and changes to this circuit. The effects of DTR states and changes are also very dependent upon the &Q command that is in effect. The test modes associated with certain &T commands are only affected by DTR changes when &D3 is in effect and are not affected by &Q command options. Below, DTR-related behaviors are defined in relation to the &D and &Q commands in effect in smart mode. In dumb mode, the behavior is as defined below for &D2 regardless of the actual &D command in effect.

DTR Behaviors in Smart Mode
----------------------------------------------------
        &D0         &D1        &D2         &D3
&Q0     none        E          I, H        R
&Q1     H           E          I, C, H     R
&Q2     I, D, H     I, D, H    I, D, H     I, D, R
&Q3     I, O, H     I, O, H    I, O, H     I, O, R
&Q4     H           E          I, C, H     R
&Q5     none        E          I, S        R
&Q6     none        E          I, S        R

Legends:

Auto-Answer Function
------------------------------------------------------------------------
I The DCD circuit is ON at all times.
------------------------------------------------------------------------

DTR OFF-to-ON Effects
------------------------------------------------------------------------
D     If S1=0 and in the idle condition, DTR OFF-to-ON signals the modem
      to go off hook and start the dialing process using the dial string
      stored by the last &Z0= command. S25 does not affect the modem's
      reactions to DTR going OFF-to-ON.

O     If S1=0 and in the idle condition, DTR OFF-to-ON signals the modem
      to go off hook and start the originate handshake process. S25 does
      not affect the modem's reactions to DTR going OFF-to-ON.

C     Following a CONNECT result code, DTR must go ON before the time
      specified by S25 (in seconds), or CTS will not go ON and the modem
      will go to the Hangup Process, issue the NO CARRIER result code,
      at the Response Speed, and go to the idle condition.
------------------------------------------------------------------------

DTR ON-to-OFF Effects
------------------------------------------------------------------------
E     If in the on-line state, DTR ON-to-OFF signals the modem to exit
      the on-line state, issue an OK result code at the response speed,
      and go to command state, while maintaining the connection. DTR
      transitions to OFF that do not persist more than the time
      specified by S25 will not cause the modem to exit the on-line
      state.

H     If in the on-line state, or in the handshaking, dialing, or
      answer process, DTR ON-to-OFF signals the modem to execute the
      hangup process, issue an OK result code at the response speed,
      and go to the idle condition. The modem is not reset by DTR. This
      will also abort any dial, handshake, or answer in progress. DTR
      transitions to OFF that do not persist more than the time
      specified by S25 will not trigger a transition to the hangup
      process.

R     DTR ON-to-OFF signals the modem to immediately perform a hard
      reset regardless of state. All processes are aborted. S25 does not
      affect the modem's reactions to DTR going OFF-to-ON. There is no
      result code.

S     If in on-Line, or in the handshaking, dialing processes, or answer
      process, a transition of DTR ON-to-OFF signals the modem to shut
      down the communications link. When the modem has completed
      transmitting the data placed into its buffer by the DTE and has
      completed sending the received data to the DTE, the modem will
      execute the hangup process, issue an OK result code at the
      response speed, and remain idle in the command state. The modem is
      not reset by DTR. This will also abort any dial, handshake, or
      answer in progress. DTR transitions to OFF that do not persist
      more than the time specified by S25 will not trigger a transition
      to the hangup process.

&F - Recall Factory Profile

The &F command recalls the configuration stored and programmed in ROM at the factory. This operation completely replaces the command options and S-register values in the active configuration with those comprising the ROM configuration. For the commands and registers stored and their factory-set ROM default values, see your user documentation.

&G - Guard Tone Selection

The &G command tells the modem which guard tone, if any, to transmit while transmitting in the high band (answer mode). Guard tone is transmitted only while the modem is transmitting in the answer mode and during the answer handshake.

&G0     Guard tones disabled
&G1     550 Hz guard tone enabled (V.22, V.22bis only)
&G2     1800 Hz guard tone enabled (V.22,V.22bis only)

&J - Jack Type Selection (Auxiliary Relay Options)

The &J command designates the type of jack with which the modem is connected to the telephone line. This selection is made by changing the way the auxiliary relay is controlled. The auxiliary relay connects the A lead to the A1 lead, and is normally open.

&J0     The auxiliary relay is never closed (suitable for RJ-11, RJ-41S,
        or RJ-45S type phone jack)
&J1     The auxiliary relay is closed while modem is off hook (suitable
        for RJ-12 or RJ-13 type phone jack)

Note: To determine the jack setting for MI/MIC operation, refer to the
description of S92.

&K - Local Flow Control Options

The &Kn command is used to select the local flow control method for use when the modem is operating in error-control mode or asynchronous mode with Automatic Speed Buffering (ASB). ASB is used for communication environments requiring a "Fixed Speed Interface" between the modem and the DTE. Note that local flow control is unidirectional in &Q6 mode and bidirectional in &Q5 mode.

S39 stores the current flow control setting. Flow control is always inhibited in command state and is valid only when on-line in error-control mode. Bi-directional flow control regulates the data stream between the DTE and the modem. Specific functions depending on parameter value are as follows:

&K0     All flow control is disabled. May be selected for use during
        error-control mode at the risk of overflowing the buffers and
        losing data.

&K1     RTS/CTS flow control is enabled. Note that the DTE-to-modem
        cable must have the supporting wires. The &T19 command
        may be used by software to determine if the cable is properly
        wired.

&K2     XON/XOFF flow control is enabled. These characters are not
        programmable and are fixed at DC1 and DC3, respectively. This
        method should not be used when XON/XOFF characters will be sent
        as user data or as part of a file transfer protocol.

&K3     RTS/CTS flow control is enabled. Note that the DTE-to-modem
        cable must have the supporting wires. The &T19 command may
        be used by software to determine if the cable is properly wired.

&K4     XON/XOFF flow control is enabled. These characters are not
        programmable and are fixed at DC1 and DC3, respectively. This
        method should not be used when XON/XOFF characters will be sent
        as user data or as part of a file transfer protocol.

&K5     Transparent XON/XOFF. The data stream is controlled by
        characters DC1 and DC3. The characters DLE, DC1, and DC3 are
        made transparent by sending DLE followed by the character XORed
        (Exclusive ORed) with 21hex. See notes on &K5 transparent flow :
        control in "Appendix D: Transparent XON/XOFF Local Flow Control
        in Hayes Modems."

&L - Line Type Selection (Dial-up/Leased)

The &L1 command instructs the modem to alter its function for leased line environments. The modem will act as if S10=255 and M0 are in effect. It will not dial numbers or send answer tone. The modem must receive an X1D or A command to go on-line. The modem will then go to the dialing or answering process, respectively. Once the handshaking process is completed, the modem tries to stay in the on-line state. When it loses carrier, it returns to the dialing or answering process. Carrier level is determined in one of several techniques, depending on the particular modem. See your user documentation for information on setting carrier level.

&L0 Select Dial-up line operation
&L1 Select Leased line (Private Circuit) operation

&O - PAD Channel Selection

The &O command instructs the modem to move from AT command state to a PAD waiting state where it is ready to receive X.25 commands. A Reset operation (see Chapter Two: X.25 Communications) is performed on the selected channel. This command can be issued while off-line so that the PADs may be configured prior to making a connection.

&O0     Move to the PAD command state of the last channel accessed
        (or to channel 1 if no previous channel has been selected).
&O1     Move to the PAD command state for channel 1.
&O2     Move to the PAD command state for channel 2.
&O3     Move to the PAD command state for channel 3.
&Q4     Move to the PAD command state for channel 4.

&Q - Communications Mode Options

The &Q command selects the communication mode. The &Q command determines how the modem will treat transmitted and received data while in the on-line state (i.e., asynchronous, synchronous, AutoSync, or error-control) and establishes certain call setup procedures. Refer also to the &C, &D, and &S commands in this section.

Command     On-Line State       Special Features
------------------------------------------------------------------------
&Q0         Asynchronous        DCD and DSR behaviors are unique. Refer
                                to &C and &S commands.

&Q1 Synchronous DTR must be ON after CONNECT when timer
value in S25 expires.

&Q2         Synchronous         DTR OFF-to-ON executes dialing process;
                                the D command invalid DTR ON-to-OFF
                                executes the hangup process; the A
                                command is invalid.

&Q3         Synchronous         Dialing and Voice allowed from phone set
                                when DTR is OFF. DTR OFF-to-ON executes
                                the handshaking process (in originate
                                mode); the D command is invalid. DTR ON-
                                to-OFF executes hangup process; the
                                A command invalid.

&Q4         Hayes AutoSync      DTR must be ON after CONNECT when
                                timer equal to S25 expires. DTE
                                data speed is 9600 bps which is not
                                equal to response speed or line
                                speed, yet all result codes are at
                                the response speed.

&Q5         Error-control       This enables error-control. Depending
                                which Hayes product is being used, any one
                                of the several point-to-point protocols
                                can be negotiated: LAPB, LAPM, X.25 or
                                MNP. After the modem handshake is
                                complete, feature negotiation (see
                                S48) is used to determine which protocol
                                (see S46) will be used for the
                                communication session.
                                If no common protocol is found
                                between the local and remote
                                modems, the fall back options (see
                                S36) will be used.

&Q6          Buffered           Automatic Speed Buffering is useful
             Asynchronous       for DTEs that cannot adjust to
                                changing transmission speeds. This
                                mode ensures the DTE-modem speed is
                                set at a constant rate regardless
                                of the line speed determined during
                                the modem handshake. With the exception
                                of flow control (&Kn) between the DTE
                                and the attached modem, this mode is
                                identical to the standard asynchronous
                                mode (&Q0). ASB operation is also a fall
                                back option (see S36) when the modem is
                                set for error-control mode (&Q5). Because
                                the DTE and DCE speeds are different in
                                ASB, a 256 byte buffer is provided so
                                that flow control does not occur on
                                every character transmission. Some DTEs
                                are sensitive to the buffer size so
                                S-registers are provided to control the
                                lower (S49) and upper (S50) boundaries.

&R - RTS/CTS Options

The functions of CTS and RTS in synchronous modes (&Q1, &Q2, and &Q3)
are determined by the &R command. The &R command has no effect if &Q0,
&Q4, &Q5, or &Q6 is in effect. See also the discussion of the CTS and
RTS signals in Appendix A. Refer to the &K command for other RTS and CTS
functions. Note when &Q4 is in effect (AutoSync operation), RTS and CTS
behaviors are not unlike those specified by RS-232/CCITT V.24.

In Synchronous Modes (&Q1, &Q2, and &Q3):
&R0     CTS tracks RTS while the modem is in on-line state and observes
        the RTS-to-CTS delay determined by S26.
&R1     CTS is ON while the modem is in the On-Line State, and RTS is
        ignored.

In other modes (&Q0, &Q4, &Q5, and &Q6), the &R option in effect does not control the RTS and CTS functions.

&S - Data Set Ready Options

The &S command controls the functions of the DSR circuit. The DSR circuit (pin 6 of the RS-232 interface) indicates when the modem is connected to a communication channel and is ready.

In synchronous mode, when originating a call, DSR goes high when dialing is completed and an answer tone is detected from the remote modem. When answering a synchronous call, DSR goes high when the modem begins transmitting the answer tone.

In asynchronous or error-control mode, the &S command can be used to configure the modem to keep the DSR signal high at all times or to have it operate according to the RS-232 specification (as described in Appendix A).

When &Q0, &Q5, and &Q6 are in effect:
&S0     DSR circuit is always on.
&S1     DSR=0 in the idle state and when in a test mode. DSR circuit is
        turned ON at start of the handshaking process. DSR is turned
        OFF when hangup process is started.
&S2     DSR=0 in the idle state and when in a test mode. DSR circuit is
        turned ON at end of handshake prior to issuing of the CONNECT
        result code. DSR is turned OFF when hangup process is started.

When &Q1 to &Q4 are in effect:
&S0-1     DSR=0 in the command state and at idle. DSR circuit is turned
          ON at start of the handshaking process. DSR is turned OFF when
          hangup process is started.
&S2       DSR=0 in the command state and at idle. DSR circuit is turned
          ON at end of handshake prior to issuing of the CONNECT result
          code. DSR is turned OFF when hangup process is started.

&T - Test Options

The following &T command options are used to configure and place the modem in various test modes as defined by CCITT V.54. These tests can be used to verify the analog and digital portions of the modem's operation, as well as those of the remote modem. Some of these tests require a connection be established before running the procedure. The &T19 command (not a CCITT V.54 test) can be used to test the RTS/CTS functions of the cable used to attach the modem to the DTE.

Note: &T commands can only be used when the modem is configured for &Q0 <CR> (unbuffered asynchronous mode).

&T0 - Terminate Test In Progress

If a V.54 Loopback Test is in progress as a result of executing an &Tn command, then the &T0 command will cause that test to be terminated provided that the modem is in the command state, or a V.54 state that accepts commands from the DTE. See specific &T command descriptions for termination actions. &T1 - Initiate Local Analog Loopback

The modem goes on hook and configures itself for analog loopback (using low frequency band if no suffix or "O" suffix, and high frequency band if "A" suffix). DSR is turned off (if &S1 is in effect), the analog loopback state is entered, and the test timer is set to the value in S18. A CONNECT result code is sent to the DTE, and the test timer then begins its count down. The test terminates when the test timer expires. If S18 equals 0, then the test must be terminated by an &T0, H0, or Z command. While any command may be entered while the modem is in this test state, the modem response is not specified except for H0, &T0, and Z - any of which will terminate the test. Upon termination of the test, the modem enters the command state.

Result Codes Description

------------------------------------------------------------------------

CONNECT When local analog loopback state is entered.

ERROR If any other &Tn test is active (except &T0) or if in

the on-line command state.

OK After test is stopped by test timer, the H0 command,

or the &T0 command.

&T3 - Perform Local Digital Loopback

Result Codes    Description
-----------------------------------------------------------------------
OK              After 2s delay.
ERROR           If any other self test is active (&T1,&T6-&T8) or if
                in idle state.
OK              When test is terminated.

&T4 - Grant RDL Requests

When in the on-line state the modem will honor a remote digital loopback request from a distant modem if it occurs. This will result in an ERROR if the command is given while any V.54 test is active (&T1, &T3, &T6, &T7, or &T8). &T5 - Deny RDL Requests

The modem will not respond to a remote digital loopback request from a distant modem. This will result in an ERROR if the command is given while any V.54 test is active (&T1, &T3, &T6, &T7, or &T8). &T6 - Initiate Remote Digital Loopback

The command is valid only if the modem is in the command state with a connection at 1200 or 2400 bps. The modem sends the remote digital loopback request signal to the distant modem (see CCITT V.22 and V.54). After the RDL acknowledgment signal is received from the distant modem, DSR is turned off (if &S1 is in effect), the on-line state is entered, a CONNECT result code is sent to the DTE, and the test timer is set to the value in S18.

If the modem does not receive the RDL acknowledgment signal from the distant end in three seconds, it sends an ERROR result code to the DTE and returns to the command state. The modem sends the signal specified in CCITT V.22 to release the remote digital loopback when the test is terminated. The test may be terminated by the H0, Z, or &T0 command. The test will also terminate when the test timer expires (sending the modem to the command state) or carrier is lost (causing a NO CARRIER result code and the modem to go on hook in the command state).

Result Codes Description

------------------------------------------------------------------------

CONNECT When on-line state is entered.

ERROR If any V.54 test is active (&T1, &T3, &T6-&T8).

ERROR If not in on-line command State.

ERROR If command is issued at other than 1200 or 2400 bps.

ERROR If the RDL signal is not acknowledged.

&T7 - Initiate RDL With Self Test

The command is only valid if the modem is in the command state with a connection at 1200 or 2400 bps. The modem sends the remote digital loopback request signal to the distant end (see CCITT V.22). After the RDL acknowledgment signal is received from the distant end, DSR is turned off (if &S1 is in effect), the on-line state is entered, an OK result code is sent to the DTE, and the test timer is set to the value in S18. While the test is active the modem sends a test message to the distant end and counts the errors in the received (looped back) signal.

The modem stays in the command state during the test. When the test is terminated (except by a loss of carrier), the modem sends the release signal to the distant end, as in &T6, and reports the three-digit error count to the DTE. The information text is followed by an OK result code. See the V command for formats. The test is terminated by loss of carrier, or an H0, &T0, or Z command, and by the S18 timer running out.

Result Codes Description

------------------------------------------------------------------------

OK When command executed is started.

OK After error count is sent to DTE.

ERROR If any other self test is active (&T1,&T3,&T6-&T8).

ERROR If not in on-line command state.

ERROR If command is issued at other thatn 1200 or 2400 bps.

ERROR If the RDL signal is not acknowledged.

&T8 - Local Loopback With Self Test

The modem goes on hook and is configured for analog loopback (low frequency band if none or O suffix, high frequency band if A suffix). The test timer is started at the time indicated by S18, DSR is turned off (if &S1 is in effect). A self test condition is entered, and an OK result code is sent to the DTE. During the test the modem sends a test message and counts errors in the looped back signal. The test is terminated when the timer times out (S18) or the &T0, H0, or Z command is issued. When the test is terminated, the three-digit error count is sent to the DTE. An OK result code follows the error count.

Result Codes: Description

------------------------------------------------------------------------

OK If a self test state is entered.

OK After error count is sent to DTE.

ERROR If any other V.54 test is active &T1,&T3,&T6,&T7),

or if on-line.

&T19 - Perform RTS/CTS Cable Test

&T19 in the modem works interactively with the DTE to confirm the RTS and CTS signal. Only the DTE can detect CTS, and only the modem can detect RTS. The modem cannot verify both signals without the active involvement of the DTE software.

The modem performs the following algorithm in response to the AT&T19<CR> command:

The following algorithm is used by Hayes Smartcom software in its use of the &T19 test:

1. Issue AT&T19 <CR>

Note: For more predictable timing, do not combine other commands on the same command line with &T19. Also, higher DTE port speeds improve the timing resolution.

2. Wait 500ms for CTS to drop. If CTS does not drop in that time, then
the test fails.

3. If CTS drop is detected, then:
      a. Drop RTS, wait 50ms, raise RTS, wait 50ms, repeat up to 6
      times, or until CTS is detected high.
      b. If CTS is detected returning high before 6 iterations, then the
      test is passing (and an OK result code may be expected soon), or
      if all 6 iterations did not result in CTS being raised, then the
      RTS part of the test is failing (and an ERROR result code may be
      expected after the 500ms timer expires).

4. Process the result code from the modem. Success during Step 3 above
    and an OK result code implies that RTS and CTS are both wired
    correctly. Failure during Step 3 or an ERROR result code implies
    that either RTS or CTS is not wired in the cable.

Note: Keep in mind that the result code may arrive while you are still
in Steps 2 and 3 above.

A modification to the software algorithm could be made to permit
software to detect which signal is missing from the cable. After issuing
the AT&T19 <CR> command, give the modem about 100ms to drop CTS. Then,
even if the CTS drop is not detected, proceed to toggle RTS anyway,
keeping in mind that the CTS part of the test has failed.

RTS/CTS flow control is preferred because it is "out of band", that is,
it does not consume any of the 256 serial codes from the user data.
XON/XOFF flow control uses DC1 (ASCII 17) and DC3 (ASCII 19). If RTS/CTS
is not supported, then Transparent Flow Control (&K5) is the next best
option (IF the software supports it) because it accomplishes Xon/Xoff
flow control without interfering with the user data (e.g. during binary
file transfers).

&U - Trellis Coding Options

The &U command is used to enable and disable Trellis coding for V.32 connections. Trellis coding is a method of forward error correction that adds information to the base modulation scheme to record successive dependencies between transmitted signal points. This selection affects V.32 9600 bps and 4800 bps transmissions only.

&U0 Enable Trellis coding
&U1 Disable Trellis coding

&V - View Configuration Profiles

The &V command is used to display the active and stored profiles (commands and S-register settings) along with any stored telephone numbers. Input from the DTE is ignored while this view configuration information is being sent to the DTE.

The example below illustrates typical &V information supplied when the factory-set default configuration profile is loaded and then stored into the stored profiles, and an arbitrary phone number is stored in one of the stored numbers locations. Note that the contents and structure of these profiles vary from modem to modem.

ACTIVE PROFILE:
B0 B41 B60 E1 L2 M1 N1 P Q0 V1 W0 X4 Y0 &C0 &D0 &G0 &J0 &K3 &Q5
&R0 &S0 &T4 &U0 &X0 &Y0
S00:000 S01:000 S02:043 S03:013 S04:010 S05:008 S06:002 S07:030 S08:002
S09:006
S10:014 S11:070 S12:050 S18:000 S25:005 S26:001 S36:005 S37:000 S38:020
S44:003
S46:002 S48:007 S49:008 S50:016 S95:000

STORED PROFILE 0:
B0 B41 B60 E1 L2 M1 N1 P Q0 V1 W0 X4 Y0 &C0 &D0 &G0 &J0 &K3 &Q5 &R0 &S0 &T4 &U0 &X0
S00:000 S02:043 S06:002 S07:050 S08:002 S09:006 S10:014 S11:095 S12:050 S18:000
S25:005 S26:001 S36:005 S37:000 S38:020 S44:003 S46:002 S48:007 S49:008 S50:016

STORED PROFILE 1:
B0 B41 B60 E1 L2 M1 N1 P Q0 V1 W0 X4 Y0 &C0 &D0 &G0 &J0 &K3 &Q5 &R0 &S0 &T4 &U0 &X0
S00:000 S02:043 S06:002 S07:050 S08:002 S09:006 S10:014 S11:095 S12:050 S18:000
S25:005 S26:001 S36:005 S37:000 S38:020 S44:003 S46:002 S48:007 S49:008 S50:016

TELEPHONE NUMBERS:
0=
1=T9W14045551212
2=
3=

The three-digit numbers after each S-register number are decimal representations of the S-register contents.

&V6 - View Blacklisting Entries

This command displays "blacklisted" telephone numbers, the number of attempts to each listed number, and the number of calls attempted since the last connection to a modem. Note that this command is only available in modems subject to "blacklisting" regulations set by certain modem approval agencies. Refer to the your user documentation to see if this command applies.

&W - Write Active Profile to Memory

The &W command stores certain command options and S-register values into one of the modem's two nonvolatile stored profile memory locations. The command options and register values stored depend on the particular modem. These are indicated in the user documentation for your modem. In addition, the AT speed and parity are stored, according to the values used at the time the command is issued.

&W0 Store the Active Profile into Stored Profile 0
&W1 Store the Active Profile into Stored Profile 1

&X - Synchronous Transmit Clock Source

The &X command determines how the DTE transmit clock is generated while the modem is in the synchronous mode.

&X0     Modem generates the transmit clock and applies it to pin 15
        (RS-232).
&X1     DTE generates the transmit clock on pin 24 (EIA 232D) and the
        modem applies this clock to pin 15 (EIA 232D). This setting
        is available for external modems only.
&X2     Modem derives the transmit clock from the receive carrier
        signal and applies it to pin 15 (RS-232).

&Y - Select Stored Profile For Hard Reset

The &Y command selects which stored profile will be copied into the active profile subsequent to a hard reset (including power-up). The &Y command execution is nonvolatile, stored at the time the command is executed, not by the &W command. The value selected with this command is not affected by the &F command, although &Y0 is selected as part of the overall factory setup.

&Y0 Select Stored Profile 0 on power-up
&Y1 Select Stored Profile 1 on power-up

&Zn=x - Store Telephone Number

The &Zn=x command is used to store up to four dialing strings in the modem's nonvolatile memory for later dialing. The format for the command is &Zn="stored number" where n is the location 0-3 to which the number should be written. For example, the line AT&Z2=5552368<CR> writes 5552368 as the third of four possible numbers to the modem's "telephone book" in nonvolatile memory. The &Zn=x command can be used to store a number with as many as 36 characters.

Any dialing string can be saved except the S dialing modifier (this would cause a stored dialing string to attempt to dial another stored string), or the ; modifier if used for automatic dialing in synchronous mode 2. If no dial string follows the command, the referenced stored number will be cleared.

&Z     <dial string><CR>
&Z=    <dial string><CR>
&Zn=   <dial string><CR>     ... where n=0-3

If the delimiter (=) is not present, the characters following the &Zn=x are treated as telephone numbers and/or modifiers and are stored in location 0. For example, in &Znxxxx, the n is a part of the phone number. If the delimiter is present the characters following it are stored in the location specified by the character preceding the delimiter (which must be in the range 0-3). If no character precedes the delimiter, the number is stored in location 0. If an invalid location is specified (n) the modem sends an ERROR result code.

Characters not listed above as storable are ignored. For example, the command &Z1=3456H;AX would store 3456;A.