AT Command Manual for model FMSE336VSP

With the single exception of the A/ command, all commands to the modem begin with the characters AT, and end with a carriage return character, hence the name AT commands. The general format of an AT command is: AT<command string> where <command string> represents zero or more commands described in this manual. The <command string> can be null, resulting in the simple sequence "AT". This sequence, often called the attention command, is useful for checking that communication is established between an application program and the modem. The response to the AT command is always OK, providing positive indication of proper operation. It may be useful to issue the AT command several times, with a brief pause (100 ms. or so) between commands, until the OK response is received. Since the AT command string has no other effect except to elicit the OK response, it can be used whenever the modem is in command mode. The AT portion of an AT command can be in upper case or lower case, but not mixed case, thus AT or at, but not At or aT". The <command string> portion is independent of case. The <command string> may contain space characters, which are ignored.

AT commands are executed by the modem only when the modem is in "command mode". While connected to a distant modem and exchanging data, the modem is in "data mode". The principle difference is that while in data mode, the modem transmits everything sent to it to the distant modem, and it does not act upon any command-like sequences that might happen to be embedded in the stream of characters. In order to issue a command to the modem, such as a command to terminate the connection, it is necessary to shift the modem from data mode to command mode. This is accomplished by issuing the Time-Independent Escape Sequence (T.I.E.S.): +++ AT<valid command string> The modem will return to command mode and immediately execute <valid command string>, then remain in command mode. It is possible, and occasionally useful, to issue the T.I.E.S. with the null <command string>: "+++ AT", causing the modem to immediately enter command mode. If it is connected to a distant modem it will remain connected. To return to data mode, issue the command "ATO".

**Table 1. AT Command Set**
Command	Function
AT	Attention - this precedes all commands except A/
A/	Execute previous command The "A/" command is not issued as part of a <command string>, but stands by itself. In other words, it is not preceded by AT and it is not followed by a <CR>. The effect of A/ is to repeat the most recent previous <command string>. This command is useful, for instance, when manually dialing a busy telephone number.
A	Answer Command Causes the modem to go off hook. If a call is coming in, the modem will try to answer it. The procedure for answering a call is a short silence and then an answer tone. Sending a character to the modem during this procedure will abort the answer procedure. The amount of time the modem will wait for a carrier is programmable by modifying the S7 register.
D	Dial Command D alone will take the modem off-hook and wait for a dial tone. (See X command for exceptions) The length of time to wait for a dialtone before dialing is programmable in register S6.
Dmn	ATDmn will dial a phone number where m is a modifier: It will dial the telephone number n.
Dial Modifiers	Description of Dial Modifier
L	Dial last number
W	Wait for dial tone. If you have selected X0 or X1 (disable dial tone detection), then you can use this modifier to override that setting.
,	Pause during dial. The amount of time to pause is determined in register S8.
;	Return to command mode after dialing. It doesn't wait for carrier or hang up.
@	Wait for 5 seconds of silence. This is used to access systems that do not provide a dial tone.
!	Hook flash. Causes the modem to go on-hook for 0.5 seconds. This is used in PBX systems and for voice features like call waiting
S=(0-3)	Dials a stored number. Up to ten numbers can be stored, and the addresses are from 0 to 9. To store a number into one of these addresses, use the &Z command.
P	Causes subsequent digits to be transmitted using pulse dial signaling. Pulse dialing is the default, until changed by the T dial modifier or by the ATT command.
T	Causes subsequent digits to be transmitted as DTMF signals. (Tone dialing)
Command	Function
En	Local Echo This command enables or disables the local echo of command characters.
E0	Commands issued to the modem are not echoed to the local terminal. This only matters in the command mode. It does not affect the modems ability to send response codes.
E1	Commands are echoed to the local terminal.
Hn	Hook Switch This command controls the hook switch relay.
H0	Force modem on-hook (hang-up).
H1	Force modem off-hook (to answer or dial).
In	Identification Report information about the modem’s capabilities and nomenclature to the DTE.
I0	Report the maximum modem transmission rate. For Sierra v.34 modems, the value reported is 28800 or 33600. example: 33600 OK
I1	Reports the firmware checksum in hex value.
I2	The modem returns OK.
I3	Report the copyright notice and firmware revision and date.
I4	Report the list of capabilities of the modem.
Ln	Speaker Volume This command controls the setting of the modem’s speaker volume. The speaker reproduces dialing and connection sounds to aid the user in monitoring call progress
L0	Speaker volume low
L1	Speaker volume low
L2	Speaker volume medium
L3	Speaker volume high
Mn	Speaker On/Off This command selects speaker operation during the connect sequence until carrier is detected. The term “carrier detected” is used here to mean the completion of a successful handshake sequence.
M0	Speaker always off
M1	Speaker on until carrier detected
M2	Speaker always on
M3	Speaker off during dialing, then on until carrier detected
On	On Line Mode
O0	Return to data mode. If you have entered the command mode using the time independent escape sequence, this will put you back in data mode without going on-hook.
O1	Retrain the modem. If the line condition has changed since the original connection, retraining the modem will cause it to reconnect at the most efficient speed for the current line condition.
Qn	Responses
Q0	Enable response to DTE.
Q1	Disable response to DTE. The modem does not respond to the terminal. Issuing a command will not produce a response (unless the command is something like ATZ, which will restore this setting to default.)
Q2	Return call progress messages in originate mode, do not return call progress messages in answer mode.
Sr=n	Set S-Register Set register r to value n
Sr?	S-Register Setting Return the value of register r
Vn	Response Codes This command selects the type of response code format reported, numeric (terse) or word (verbose).
V0	Result codes will be sent in numeric form. (See the result code table)
V1	Result codes will be sent in word form. (See the result code table).
Xn	Call Progress Monitoring Response Set This command controls which Call Progress Monitor signals are monitored and reported to the local DTE.
X0	Send OK, CONNECT, RING, NO CARRIER, ERROR and NO ANSWER. Busy and Dial Tone Detection are disabled.
X1	Send X0 messages and CONNECT speed
X2	Send X1 message and NO DIALTONE
X3	Send X2 messages except NO DIALTONE, BUSY and RING BACK
X4	Send all responses
Yn	Long Space Disconnect This command disables or enables long space disconnect. In non-error correction mode, a disconnect request (ATH0, loss of DTR or DCD, etc.) will cause the modem to send a long space of four seconds before going on-hook. In error correction mode, the modem will respond to an incoming long space (longer than 1.6 seconds) by going on hook.
Y0	Disable long space disconnect
Y1	Enable long space disconnect; with error correction, hang up after sending 1.6 second long space; without error correction, hang up after 4 second long space.
&Zn	Reset And Recall Stored User Profile This command recalls the stored user configuration profile consisting of all user defined AT Com-mands and S Register settings (as stored in profile 0 or profile 1 with &W0 and &W1 commands).
Z0	Reset modem to profile 0
Z1	Reset modem to profile 1

Table 1. AT Command Set

Command

Function

Attention - this precedes all commands except A/

A/

Execute previous command
The "A/" command is not issued as part of a <command string>, but stands by itself. In other words, it is not preceded by AT and it is not followed by a <CR>. The effect of A/ is to repeat the most recent previous <command string>. This command is useful, for instance, when manually dialing a busy telephone number.

A

Answer Command
Causes the modem to go off hook. If a call is coming in, the modem will try to answer it. The procedure for answering a call is a short silence and then an answer tone. Sending a character to the modem during this procedure will abort the answer procedure. The amount of time the modem will wait for a carrier is programmable by modifying the S7 register.

D

Dial Command
D alone will take the modem off-hook and wait for a dial tone. (See X command for exceptions) The length of time to wait for a dialtone before dialing is programmable in register S6.

Dmn

ATDmn will dial a phone number where m is a modifier: It will dial the telephone number n.

Dial Modifiers

Description of Dial Modifier

L

Dial last number

W

Wait for dial tone. If you have selected X0 or X1 (disable dial tone detection), then you can use this modifier to override that setting.

,

Pause during dial. The amount of time to pause is determined in register S8.

;

Return to command mode after dialing. It doesn't wait for carrier or hang up.

@

Wait for 5 seconds of silence. This is used to access systems that do not provide a dial tone.

!

Hook flash. Causes the modem to go on-hook for 0.5 seconds. This is used in PBX systems and for voice features like call waiting

S=(0-3)

Dials a stored number. Up to ten numbers can be stored, and the addresses are from 0 to 9. To store a number into one of these addresses, use the &Z command.

P

Causes subsequent digits to be transmitted using pulse dial signaling. Pulse dialing is the default, until changed by the T dial modifier or by the ATT command.

Causes subsequent digits to be transmitted as DTMF signals. (Tone dialing)

Command

Function

En

Local Echo
This command enables or disables the local echo of command characters.

E0

Commands issued to the modem are not echoed to the local terminal. This only matters in the command mode. It does not affect the modems ability to send response codes.

E1

Commands are echoed to the local terminal.

Hn

Hook Switch
This command controls the hook switch relay.

H0

Force modem on-hook (hang-up).

H1

Force modem off-hook (to answer or dial).

In

Identification
Report information about the modem’s capabilities and nomenclature to the DTE.

I0

Report the maximum modem transmission rate. For Sierra v.34 modems, the value reported is 28800 or 33600.
example:
33600
OK

I1

Reports the firmware checksum in hex value.

I2

The modem returns OK.

I3

Report the copyright notice and firmware revision and date.

I4

Report the list of capabilities of the modem.

Ln

Speaker Volume
This command controls the setting of the modem’s speaker volume. The speaker reproduces dialing and connection sounds to aid the user in monitoring call progress

L0

Speaker volume low

L1

Speaker volume low

L2

Speaker volume medium

L3

Speaker volume high

Mn

Speaker On/Off
This command selects speaker operation during the connect sequence until carrier is detected. The term “carrier detected” is used here to mean the completion of a successful handshake sequence.

M0

Speaker always off

M1

Speaker on until carrier detected

M2

Speaker always on

M3

Speaker off during dialing, then on until carrier detected

On

On Line Mode

O0

Return to data mode. If you have entered the command mode using the time independent escape sequence, this will put you back in data mode without going on-hook.

O1

Retrain the modem. If the line condition has changed since the original connection, retraining the modem will cause it to reconnect at the most efficient speed for the current line condition.

Qn

Responses

Q0

Enable response to DTE.

Q1

Disable response to DTE. The modem does not respond to the terminal. Issuing a command will not produce a response (unless the command is something like ATZ, which will restore this setting to default.)

Q2

Return call progress messages in originate mode, do not return call progress messages in answer mode.

Sr=n

Set S-Register
Set register r to value n

Sr?

S-Register Setting
Return the value of register r

Vn

Response Codes
This command selects the type of response code format reported, numeric (terse) or word (verbose).

V0

Result codes will be sent in numeric form. (See the result code table)

V1

Result codes will be sent in word form. (See the result code table).

Xn

Call Progress Monitoring Response Set
This command controls which Call Progress Monitor signals are monitored and reported to the local DTE.

X0

Send OK, CONNECT, RING, NO CARRIER, ERROR and NO ANSWER. Busy and Dial Tone Detection are disabled.

X1

Send X0 messages and CONNECT speed

X2

Send X1 message and NO DIALTONE

X3

Send X2 messages except NO DIALTONE, BUSY and RING BACK

X4

Send all responses

Yn

Long Space Disconnect
This command disables or enables long space disconnect. In non-error correction mode, a disconnect request (ATH0, loss of DTR or DCD, etc.) will cause the modem to send a long space of four seconds before going on-hook. In error correction mode, the modem will respond to an incoming long space (longer than 1.6 seconds) by going on hook.

Y0

Disable long space disconnect

Y1

Enable long space disconnect; with error correction, hang up after sending 1.6 second long space; without error correction, hang up after 4 second long space.

&Zn

Reset And Recall Stored User Profile
This command recalls the stored user configuration profile consisting of all user defined AT Com-mands and S Register settings (as stored in profile 0 or profile 1 with &W0 and &W1 commands).

Z0

Reset modem to profile 0

Z1

Reset modem to profile 1

**Table 1. & Ampersand Commands**
Command	Function
&An	Auto Fallforward / Fallback The &A command enables or disables the modem’s capability to automatically re-negotiate the DCE line speed with changes in communication channel conditions
&A0	Disables the fallforward / fallback feature.
&A1	Enables the fallforward / fallback feature.
&Cn	Data Carrier Detect (DCD)
&C0	Force DCD on
&C1	Force DCD on after link established (i.e. V.42bis, MNP) and toggle DCD on disconnect.
&C2	DCD indicates true state of remote modem carrier signal (energy detection).
&Dn	Data Terminal Ready (DTR)
&D0	DTR is assumed on
&D1	DTR drop causes modem back to command mode without disconnecting
&D2	DTR drop causes modem to hang up
&D3	DTR drop causes modem to be initialized;&Y determines which profile is loaded.
&Fn	Recall Factory Defaults The &Fn command instructs the modem to use the factory-set parameters stored in the modem’s nonvolatile memory.
&F	Load factory profile
&F1	For factory use only. Enables Quiet mode (Q1)
&Gn	Set Maximum Line Rate
&G0	Autobaud.
&G1	Send last connect speed.
&G2	300bps.
&G3	1200bps.
&G4	2400bps.
&G5	4800bps.
&G6	7200bps.
&G7	9600bps.
&G8	12.0kbps.
&G9	14.4kbps.
&G10	16.8kbps.
&G11	19.2kbps.
&G12	21.6kbps.
&G13	24.0kbps.
&G14	26.4kbps.
&G15	28.8kbps.
&G16	31.2kbps.
&G17	33.6kbps
&Hn	Switched Network Handshake Mode By default, the modem will connect to a distant modem using “V.34 automatic” mode. The modem handshake algorithm will select the highest line rate possible, considering both modems’ capabilities and the condition of the transmission path. The modems will attempt a connection using, succes-sively, V.34, V.32 bis, V.32, V.22 bis, V.22, Bell 212, and Bell 103 protocols. The handshake algorithm can be set with the &Hn command to restrict the allowable protocols, according to the commands below.
&H0	V.34 automatic, 33,600bps to 300bps
&H1	V.34 only, 33,600bps to 2400bps
&H2	V.32 bis automatic, 14,400bps to 300bps
&H3	V.32 bis only, 14,400bps to 4800bps
&H4	V.32 automatic, 9600bps to 300bps
&H5	V.32 only, 9600bps to 4800bps
&H6	V.22 bis only, 2400bps to 1200bps
&H7	V.22 only, 1200bps
&H8	Bell 212 only, 1200bps
&H9	Bell 103, 300bps
&H10	V.21 only, 300bps
&H11	V.23 only (for interna-tional code only), Originate modem transmits at 75bps, re-ceives at 1200bps.
&Mn	Operating Mode The &M operating mode command selects asynchronous or synchronous operation.
&M0	Select asynchronous operation in both command and data mode.
&M1	For factory use only.
&Rn	CTS Operation The &R command defines the functionality of the Request To Send and Clear To Send EIA interchange circuits in direct mode.
&R0	On in command mode, CTS follows RTS in data mode on in command mode. CTS follows RTS in data mode.
&R1	Always on.
&R2	CTS and RTS implement hardware flow control.
&R3	Always on.
&Sn	Data Set Ready (DSR) Signal The &S Data Set Ready command controls how the DSR signal will operate.
&S0	DSR signal active at all times. (Toggles off at disconnect)
&S1	DSR signal active according to (normal)the CCITT / ITU-T specification.
&S2	DSR follows carrier detect.
&S3	DSR is forced on in all modes.
&Un	Trellis Coding This command allows selection of trellis coded data when the modem is in V.32 mode at 9600 BPS.
&U0	Enable trellis coding
&U1	Disable trellis coding
&V	View Active Configuration Use the &V command to display the command and S registers settings in the active and stored pro-files and any stored telephone numbers.
&V	Display active profile
&Wn	Store Active Profile The &Wn command is used to store the most recent setting of certain commands and S register val-ues into one of two nonvolatile memory locations. Commands: En Ln Mn Qn Vn Xn Yn &Cn &Dn &Rn &Sn &T0n &Un &Xn \Cn \Fn \Gn \Nn \Qn \Tn \Vn %An %Dn %En Registers: S0, S2, S3, S4, S5, S6, S7, S8, S9, S10, S12, S18, S25, S38
&W0	Save active profile to profile 0
&W1	Save active profile to profile 1
&Yn	Select Stored Power-up Profile The &Yn command tells the modem which stored profile to use when reset or powered-up.
&Y0	Use profile 0 on powerup
&Y1	Use profile 1 on powerup
&Zn=number	Store Dial String This command stores the supplied <dial string> into one of four dial string memories. the <dial string> may contain up to 36 characters taken from the dial modifiers listed under the D command.
&Zn=number	Save telephone number (up to 36 digits) into memory location n (0-3)

Table 1. & Ampersand Commands

Command

Function

&An

Auto Fallforward / Fallback
The &A command enables or disables the modem’s capability to automatically re-negotiate the DCE line speed with changes in communication channel conditions

&A0

Disables the fallforward / fallback feature.

&A1

Enables the fallforward / fallback feature.

&Cn

Data Carrier Detect (DCD)

&C0

Force DCD on

&C1

Force DCD on after link established (i.e. V.42bis, MNP) and toggle DCD on disconnect.

&C2

DCD indicates true state of remote modem carrier signal (energy detection).

&Dn

Data Terminal Ready (DTR)

&D0

DTR is assumed on

&D1

DTR drop causes modem back to command mode without disconnecting

&D2

DTR drop causes modem to hang up

&D3

DTR drop causes modem to be initialized;&Y determines which profile is loaded.

&Fn

Recall Factory Defaults
The &Fn command instructs the modem to use the factory-set parameters stored in the modem’s nonvolatile memory.

&F

Load factory profile

&F1

For factory use only. Enables Quiet mode (Q1)

&Gn

Set Maximum Line Rate

&G0

Autobaud.

&G1

Send last connect speed.

&G2

300bps.

&G3

1200bps.

&G4

2400bps.

&G5

4800bps.

&G6

7200bps.

&G7

9600bps.

&G8

12.0kbps.

&G9

14.4kbps.

&G10

16.8kbps.

&G11

19.2kbps.

&G12

21.6kbps.

&G13

24.0kbps.

&G14

26.4kbps.

&G15

28.8kbps.

&G16

31.2kbps.

&G17

33.6kbps

&Hn

Switched Network Handshake Mode
By default, the modem will connect to a distant modem using “V.34 automatic” mode. The modem handshake algorithm will select the highest line rate possible, considering both modems’ capabilities and the condition of the transmission path. The modems will attempt a connection using, succes-sively, V.34, V.32 bis, V.32, V.22 bis, V.22, Bell 212, and Bell 103 protocols. The handshake algorithm can be set with the &Hn command to restrict the allowable protocols, according to the commands below.

&H0

V.34 automatic, 33,600bps to 300bps

&H1

V.34 only, 33,600bps to 2400bps

&H2

V.32 bis automatic, 14,400bps to 300bps

&H3

V.32 bis only, 14,400bps to 4800bps

&H4

V.32 automatic, 9600bps to 300bps

&H5

V.32 only, 9600bps to 4800bps

&H6

V.22 bis only, 2400bps to 1200bps

&H7

V.22 only, 1200bps

&H8

Bell 212 only, 1200bps

&H9

Bell 103, 300bps

&H10

V.21 only, 300bps

&H11

V.23 only (for interna-tional code only), Originate modem transmits at 75bps, re-ceives at 1200bps.

&Mn

Operating Mode
The &M operating mode command selects asynchronous or synchronous operation.

&M0

Select asynchronous operation in both command and data mode.

&M1

For factory use only.

&Rn

CTS Operation
The &R command defines the functionality of the Request To Send and Clear To Send EIA interchange circuits in direct mode.

&R0

On in command mode, CTS follows RTS in data mode on in command mode. CTS follows RTS in data mode.

&R1

Always on.

&R2

CTS and RTS implement hardware flow control.

&R3

Always on.

&Sn

Data Set Ready (DSR) Signal
The &S Data Set Ready command controls how the DSR signal will operate.

&S0

DSR signal active at all times. (Toggles off at disconnect)

&S1

DSR signal active according to (normal)the CCITT / ITU-T specification.

&S2

DSR follows carrier detect.

&S3

DSR is forced on in all modes.

&Un

Trellis Coding
This command allows selection of trellis coded data when the modem is in V.32 mode at 9600 BPS.

&U0

Enable trellis coding

&U1

Disable trellis coding

&V

View Active Configuration
Use the &V command to display the command and S registers settings in the active and stored pro-files and any stored telephone numbers.

&V

Display active profile

&Wn

Store Active Profile
The &Wn command is used to store the most recent setting of certain commands and S register val-ues into one of two nonvolatile memory locations. Commands: En Ln Mn Qn Vn Xn Yn &Cn &Dn &Rn &Sn &T0n &Un &Xn \Cn \Fn \Gn \Nn \Qn \Tn \Vn %An %Dn %En Registers: S0, S2, S3, S4, S5, S6, S7, S8, S9, S10, S12, S18, S25, S38

&W0

Save active profile to profile 0

&W1

Save active profile to profile 1

&Yn

Select Stored Power-up Profile
The &Yn command tells the modem which stored profile to use when reset or powered-up.

&Y0

Use profile 0 on powerup

&Y1

Use profile 1 on powerup

&Zn=number

Store Dial String
This command stores the supplied <dial string> into one of four dial string memories. the <dial string> may contain up to 36 characters taken from the dial modifiers listed under the D command.

&Zn=number

Save telephone number (up to 36 digits) into memory location n (0-3)

**Table 1. % Percent Commands**
Command	Function
%An	Set Error Control Abort Character %An sets the ASCII character which may be sent during error control negotiation to abort negotiation and return to standard buffered mode. Range: 0 to 127 Response: OK Default: 013 (<cr>)
%Cn	Enable or Disable Data Compression
%C0	Disable V.42bis operation and MNP Class 5 data compression
%C1	Enable V.42bis operation and MNP Class 5 data compression, both directions.
%C2	Enable in transmit path only in V.42 bis.
%C3	Enable in receive path only in V.42 bis.
%Dn	DSR Operation In Test Mode
%D0	Force DSR On during ITU-T V.54 Loop 3 test (ANALOOP).
%D1	Force DSR Off during this test.
%Kn	Character Abort
%K0	Two second delay to character abort.
%K1	Disable.
%On	Answer Mode
%O0	Answer mode if ringing.
%O1	Force to answer mode.
%O2	Automatic answer in originate mode.
%Q	Retrain On Poor Signal Quality
%Q0	Disables retrain initiation.
%Q1	Attempt up to 3 consecutive retrains; disconnect if not successful.
%Q2	Retrain until signal quality is good.
%Rn	Set Maximum Line Rate Set the maximum speed at which the modem will communicate with the distant DCE according to the value of n, as shown below.
%R0	autobaud, speed
%R1	last connect speed
%R2	300
%R3	1,200
%R4	2,400
%R5	4,800
%R6	7,200
%R7	9,600
%R8	12,000
%R9	14,400
%R10	16,800
%R11	19,200
%R12	21,600
%R13	24,000
%R14	26,400
%R15	28,800
%R16	31,200
%R17	33,600
%Zn	DTR Dialing
%Z0	Ignore.
%Z1=x	Dial cell x.
%Z2	Go Off Hook and attempt to handshake.

Table 1. % Percent Commands

Command

Function

%An

Set Error Control Abort Character
%An sets the ASCII character which may be sent during error control negotiation to abort negotiation and return to standard buffered mode. Range: 0 to 127
Response: OK
Default: 013 (<cr>)

%Cn

Enable or Disable Data Compression

%C0

Disable V.42bis operation and MNP Class 5 data compression

%C1

Enable V.42bis operation and MNP Class 5 data compression, both directions.

%C2

Enable in transmit path only in V.42 bis.

%C3

Enable in receive path only in V.42 bis.

%Dn

DSR Operation In Test Mode

%D0

Force DSR On during ITU-T V.54 Loop 3 test (ANALOOP).

%D1

Force DSR Off during this test.

%Kn

Character Abort

%K0

Two second delay to character abort.

%K1

Disable.

%On

Answer Mode

%O0

Answer mode if ringing.

%O1

Force to answer mode.

%O2

Automatic answer in originate mode.

%Q

Retrain On Poor Signal Quality

%Q0

Disables retrain initiation.

%Q1

Attempt up to 3 consecutive retrains; disconnect if not successful.

%Q2

Retrain until signal quality is good.

%Rn

Set Maximum Line Rate
Set the maximum speed at which the modem will communicate with the distant DCE according to the value of n, as shown below.

%R0

autobaud, speed

%R1

last connect speed

%R2

300

%R3

1,200

%R4

2,400

%R5

4,800

%R6

7,200

%R7

9,600

%R8

12,000

%R9

14,400

%R10

16,800

%R11

19,200

%R12

21,600

%R13

24,000

%R14

26,400

%R15

28,800

%R16

31,200

%R17

33,600

%Zn

DTR Dialing

%Z0

Ignore.

%Z1=x

Dial cell x.

%Z2

Go Off Hook and attempt to handshake.

**Table 1. \ Backslash Commands**
Command	Function
\An	Overspeed Correction (For factory use only!)
\A0	1.25% (nominal) asynchronous overspeed correction.
\A1	2.5% (extended) overspeed correction.
\Bn	Character Format The \B command sets up the character length and format the modem uses in front ends that do not send AT commands. Character format is determined by the value of n according to the following table.

Table 1. \ Backslash Commands

Command

Function

\An

Overspeed Correction (For factory use only!)

\A0

1.25% (nominal) asynchronous overspeed correction.

\A1

2.5% (extended) overspeed correction.

\Bn

Character Format
The \B command sets up the character length and format the modem uses in front ends that do not send AT commands. Character format is determined by the value of n according to the following table.

numeric response	word response	meaning
0	OK	command was successful
1	CONNECT	link established
1	CONNECT	link established at 300
2	RING	incoming ring detected
3	NO CARRIER	link dropped
4	ERROR	command failed
5	CONNECT 1200	link established at 1200
6	NO DIALTONE	dial tone not present
7	BUSY	line busy
8	NO ANSWER	remote not answering
10	CONNECT 2400	link established at 2400
11	CONNECT 4800	link established at 4800
12	CONNECT 9600	link established at 9600
14	CONNECT 19200	link established at 19200
15	CONNECT 7200	link established at 7200
16	CONNECT 12000	link established at 12000
17	CONNECT 14400	link established at 14400
18	CONNECT 16800	link established at 16800
19	CONNECT 21600	link established at 21600
20	CONNECT 24000	link established at 24000
21	CONNECT 26400	link established at 26400
22	CONNECT 28800	link established at 28800
23	CONNECT 31200	link established at 31200
24	CONNECT 33600	link established at 33600

numeric response	word response	meaning
1	CONNECT	DTE link at 300
5	CONNECT 1200	DTE link at 1200
10	CONNECT 2400	DTE link at 2400
11	CONNECT 4800	DTE link at 4800
15	CONNECT 7200	DTE link at 7200
12	CONNECT 9600	DTE link at 9600
16	CONNECT 12000	DTE link at 12000
17	CONNECT 14400	DTE link at 14400
18	CONNECT 16800	DTE link at 16800
14	CONNECT 19200	DTE link at 19200
19	CONNECT 21600	DTE link at 21600
20	CONNECT 24000	DTE link at 24000
21	CONNECT 26400	DTE link at 26400
22	CONNECT 28800	DTE link at 28800
23	CONNECT 31200	DTE link at 31200
24	CONNECT 33600	DTE link at 33600
25	CONNECT 38400	DTE link at 38400
26	CONNECT 57600	DTE link at 57600
27	CONNECT 76800	DTE link at 76800
28	CONNECT 115200	DTE link at 115200
29	CONNECT 128000	DTE link at 128000

numeric response	word response	meaning
70	PROTOCOL:NONE	no protocol
80	PROTOCOL:ALTERNATE	MNP protocol
82	PROTOCOL:ALTERNATE, CLASS 2	MNP class 2
24	PROTOCOL:ALTERNATE, CLASS 2 + CLASS 4	MNP class 2 + 4
245	PROTOCOL:ALTERNATE, CLASS 2 +CLASS 4 +CLASS 5	MNP class 2 + 4 + 5
83	PROTOCOL:ALTERNATE, CLASS 3	MNP class 3
34	PROTOCOL:ALTERNATE, CLASS 3 +CLASS 4	MNP class 3 + 4
345	PROTOCOL:ALTERNATE, CLASS 3 +CLASS 4 +CLASS 5	MNP class 2 + 4 + 5
77	PROTOCOL:V.42	v.42 protocol
79	PROTOCOL:V.42BIS	v.42 bis protocol

numeric response	word response	meaning
30	CONNECT REL	reliable DCE link at 300
31	CONNECT 1200/REL
32	CONNECT 2400/REL	reliable DCE link at 2400
33	CONNECT 4800/REL	reliable DCE link at 4800
34	CONNECT 7200/REL	reliable DCE link at 9600
35	CONNECT 9600/REL	reliable DCE link at 19200
36	CONNECT 12000/REL	reliable DCE link at 9600
37	CONNECT 14400/REL	reliable DCE link at 12000
38	CONNECT 16800/REL	reliable DCE link at 14400
39	CONNECT 19200/REL	reliable DCE link at 16800
40	CONNECT 21600/REL	reliable DCE link at 21600
41	CONNECT 24000/REL	reliable DCE link at 24000
42	CONNECT 26400/REL	reliable DCE link at 26400
43	CONNECT 28800/REL	reliable DCE link at 28800
44	CONNECT 31200/REL	reliable DCE link at 31200
45	CONNECT 33600/REL	reliable DCE link at 33600

**Table 4. S-Registers**
An S-Register can affect an AT Command. For example, the &T command will initiate a test but register S18 determines the test time. This section defines the S-Registers supported by the Sierra V.34 modem chip sets, describes the format, de-fault setting, and the range of possible settings. S-Registers can be displayed and/or modified when the modem is in the command mode. To display the value of an S-Register, type: ATSn? (where n is the register number) then press: Enter. To modify the value of the S- Register, type: ATSn=r (where n is the register number and r is the new value) then press: Enter.
Register	Function
0	Rings to auto-answer Set the number of rings required before the modem answers. 0 setting disables auto-answer. Range: 0 - 255 rings Default: 0 (auto-answer disabled)
1	Ring counter Count the number of rings before the modem answers.This register resets approximately 8 seconds after the last ring. Range: 0 - 255 rings Default: 0
2	Escape character Define the character used for the three-character escape code sequence,used to switch the modem from Data Mode to Command Mode without losing the connection to the remote modem. Values greater than 127 disable the escape feature, preventing a return to the Command Mode. If the modem will be used to automatically answer incoming calls (BBS), either disable the escape characters or set them to a value other than that used by the originating modem. To return to Command Mode with the escape characters disabled, the remote modem must hang up or an ON-to-OFF transition of the DTR interface signal must occur with the &D1, &D2, or &D3 command in effect. Range: 0 - 255 Default: 43 (+)
3	Carriage return character Define the character for carriage return. This is the character used to end the command line (and have the modem execute the line) and also the character that appears after the modem sends a response. Range: 0 - 127 Default: 13 (carriage return)
4	Line feed character Define the character for line feed. The modem sends the line feed character after a carriage return only when word responses are sent (V1 command in effect). If a line feed character is not wanted, change the register value to a null character (the line feed character cannot be totally disabled). Range: 0 - 127 Default: 10 (line feed)
5	Backspace character Define the character for backspace. This character is both the character created by pressing the Backspace key and the character echoed to move the cursor to the left. To change the register value, assign an ASCII value be-tween 0 and 32, or greater than 127. Do not use values between 33 and 126 since they correspond to printable ASCII characters. Range: 0 - 127 Default: 8 (backspace)
6	Wait before dialing When the modem executes a Dial command line with the X0, X1, or X3 response set in effect, Register S6 tells the modem how long to wait after going off-hook before it dials the first digit in the Dial command line. This feature is convenient when it takes longer than two seconds to obtain a dial tone. If the modem does not detect a dial tone when the time in Register S6 elapses, you will receive the NO DIALTONE (or 6) response. Range: 2 - 255 seconds Default: 2 seconds
7	Wait for carrier after dial Set the length of time that the modem waits for a carrier from the remote modem before hanging up. The register value can be increased if the modem does not detect a carrier within the specified time. If the modem detects a remote carrier signal within the specified time, it sends a CONNECT response and enters Data Mode. If it does not detect a remote carrier signal within the specified time, it sends the NO CARRIER (or 3) response, hangs up and returns to the Command Mode. Range: 1 - 255 seconds Default: 60 seconds
8	Pause time for dial delay Set the length of time to pause for the pause dial modifier ",". The comma is used when dialing through a PBX or other special telephone service to wait for an outside telephone line. An alternative to changing this register value is to include more than one comma in your command line. Range: 0 - 255 seconds Default: 2 seconds
9	Carrier detect response time Define the length of time a signal is detected and qualified as a carrier. The factory setting requires the modem to listen to the carrier signal for at least 0.6 seconds before recognizing it. Increasing the time in this register reduces the chances that the modem will mistake noise such as a busy signal or voice for a carrier signal. For example, entering a value 15 means that the remote modem’s carrier signal must be present for 1.5 seconds for the modem to recognize it. Range: 1 - 255 tenths of a second Default: 6 (0.6 second)
10	Lost carrier hang up delay Set the length of time the modem waits before hanging up for a carrier loss. This allows the remote modem’s carrier signal to momentarily disappear from the telephone line without the modem disconnecting. To have the modem ignore the Data Carrier Detect status and act as if the remote modem’s carrier signal is always present, set the value to 255. Assigning a value smaller in Register S10 than the value in Register S9 causes the modem to disconnect when it detects a momentary carrier loss, because Register S10 expires before the carrier response time expires. Range: 1 - 255 tenths of a second Default: 14 (6 seconds)
11	DTMF speed control Set the length of tone and the time between tones for the tone dialing. Range: 50 - 255 milliseconds Default: 75 milliseconds
12	Escape Prompt Delay (EPD) timer Set the time from detection of the last character of the three character escape sequence until the "OK" is returned to the DTE Range: 0 - 255 fiftieths of a second Default: 50 (1 second)
25	Delay to DTR If the &M1 command is in effect, Register S25 specifies the number of seconds that the modem waits after a connection has been made before examining the DTR lead. This delay allows an asynchronous terminal to be detached from the modem and a synchronous terminal connected while remaining in the Data Mode. After this delay S25 reverts to hundredths of seconds. Range: 0 - 255 hundredths of a second Default: 5 (0.05 second)
38	Delay before forced hang up Register S38 specifies the number of seconds the modem waits when in error-control mode before disconnecting after receiving the command to hang up or an on-to-off transition of DTR. The range for this register is 0-255 seconds; the default is 20 seconds. If the register is set to 0, the modem does not wait for data in the buffer to clear (gives NO CARRIER response). If the register is set to a value between 0 and 254, the modem will wait that number of seconds, or until all data has been transferred, before hanging up (if data clears, gives OK response; if not, gives NO CARRIER response). If the register is set to 255, the modem will not hang up until all data is transferred. Range: 0 - 255 seconds Default: 20 seconds
70	Retransmission Counter This register limits the number of times the modem will retransmit a frame while in an error correcting connection. Re-transmissions become necessary when data errors introduced by noise disrupt the reception of a frame. When the limit set by this register is reached, the modem hangs up. Raising this limit may be necessary if, for example, telephone lines are extremely noisy. The Re-transmission delays may be undesirable, but the modem will not hang up. The range of this register is 0-255, with a factory setting of 100.

Table 4. S-Registers

An S-Register can affect an AT Command. For example, the &T command will initiate a test but register S18 determines the test time. This section defines the S-Registers supported by the Sierra V.34 modem chip sets, describes the format, de-fault setting, and the range of possible settings. S-Registers can be displayed and/or modified when the modem is in the command mode. To display the value of an S-Register, type: ATSn? (where n is the register number) then press: Enter. To modify the value of the S- Register, type: ATSn=r (where n is the register number and r is the new value) then press: Enter.

Register

Function

0

Rings to auto-answer
Set the number of rings required before the modem answers. 0 setting disables auto-answer.
Range: 0 - 255 rings
Default: 0 (auto-answer disabled)

1

Ring counter
Count the number of rings before the modem answers.This register resets approximately 8 seconds after the last ring.
Range: 0 - 255 rings
Default: 0

2

Escape character
Define the character used for the three-character escape code sequence,used to switch the modem from Data Mode to Command Mode without losing the connection to the remote modem. Values greater than 127 disable the escape feature, preventing a return to the Command Mode. If the modem will be used to automatically answer incoming calls (BBS), either disable the escape characters or set them to a value other than that used by the originating modem. To return to Command Mode with the escape characters disabled, the remote modem must hang up or an ON-to-OFF transition of the DTR interface signal must occur with the &D1, &D2, or &D3 command in effect.
Range: 0 - 255
Default: 43 (+)

3

Carriage return character
Define the character for carriage return. This is the character used to end the command line (and have the modem execute the line) and also the character that appears after the modem sends a response.
Range: 0 - 127
Default: 13 (carriage return)

4

Line feed character
Define the character for line feed. The modem sends the line feed character after a carriage return only when word responses are sent (V1 command in effect). If a line feed character is not wanted, change the register value to a null character (the line feed character cannot be totally disabled).
Range: 0 - 127
Default: 10 (line feed)

5

Backspace character
Define the character for backspace. This character is both the character created by pressing the Backspace key and the character echoed to move the cursor to the left. To change the register value, assign an ASCII value be-tween 0 and 32, or greater than 127. Do not use values between 33 and 126 since they correspond to printable ASCII characters.
Range: 0 - 127
Default: 8 (backspace)

6

Wait before dialing
When the modem executes a Dial command line with the X0, X1, or X3 response set in effect, Register S6 tells the modem how long to wait after going off-hook before it dials the first digit in the Dial command line. This feature is convenient when it takes longer than two seconds to obtain a dial tone. If the modem does not detect a dial tone when the time in Register S6 elapses, you will receive the NO DIALTONE (or 6) response.
Range: 2 - 255 seconds
Default: 2 seconds

7

Wait for carrier after dial
Set the length of time that the modem waits for a carrier from the remote modem before hanging up. The register value can be increased if the modem does not detect a carrier within the specified time. If the modem detects a remote carrier signal within the specified time, it sends a CONNECT response and enters Data Mode. If it does not detect a remote carrier signal within the specified time, it sends the NO CARRIER (or 3) response, hangs up and returns to the Command Mode.
Range: 1 - 255 seconds
Default: 60 seconds

8

Pause time for dial delay
Set the length of time to pause for the pause dial modifier ",". The comma is used when dialing through a PBX or other special telephone service to wait for an outside telephone line. An alternative to changing this register value is to include more than one comma in your command line.
Range: 0 - 255 seconds
Default: 2 seconds

9

Carrier detect response time
Define the length of time a signal is detected and qualified as a carrier. The factory setting requires the modem to listen to the carrier signal for at least 0.6 seconds before recognizing it. Increasing the time in this register reduces the chances that the modem will mistake noise such as a busy signal or voice for a carrier signal. For example, entering a value 15 means that the remote modem’s carrier signal must be present for 1.5 seconds for the modem to recognize it.
Range: 1 - 255 tenths of a second
Default: 6 (0.6 second)

10

Lost carrier hang up delay
Set the length of time the modem waits before hanging up for a carrier loss. This allows the remote modem’s carrier signal to momentarily disappear from the telephone line without the modem disconnecting. To have the modem ignore the Data Carrier Detect status and act as if the remote modem’s carrier signal is always present, set the value to 255. Assigning a value smaller in Register S10 than the value in Register S9 causes the modem to disconnect when it detects a momentary carrier loss, because Register S10 expires before the carrier response time expires.
Range: 1 - 255 tenths of a second
Default: 14 (6 seconds)

11

DTMF speed control
Set the length of tone and the time between tones for the tone dialing.
Range: 50 - 255 milliseconds
Default: 75 milliseconds

12

Escape Prompt Delay (EPD) timer
Set the time from detection of the last character of the three character escape sequence until the "OK" is returned to the DTE
Range: 0 - 255 fiftieths of a second
Default: 50 (1 second)

25

Delay to DTR
If the &M1 command is in effect, Register S25 specifies the number of seconds that the modem waits after a connection has been made before examining the DTR lead. This delay allows an asynchronous terminal to be detached from the modem and a synchronous terminal connected while remaining in the Data Mode. After this delay S25 reverts to hundredths of seconds.
Range: 0 - 255 hundredths of a second
Default: 5 (0.05 second)

Delay before forced hang up
Register S38 specifies the number of seconds the modem waits when in error-control mode before disconnecting after receiving the command to hang up or an on-to-off transition of DTR. The range for this register is 0-255 seconds; the default is 20 seconds. If the register is set to 0, the modem does not wait for data in the buffer to clear (gives NO CARRIER response). If the register is set to a value between 0 and 254, the modem will wait that number of seconds, or until all data has been transferred, before hanging up (if data clears, gives OK response; if not, gives NO CARRIER response). If the register is set to 255, the modem will not hang up until all data is transferred.
Range: 0 - 255 seconds
Default: 20 seconds

70

Retransmission Counter
This register limits the number of times the modem will retransmit a frame while in an error correcting connection. Re-transmissions become necessary when data errors introduced by noise disrupt the reception of a frame. When the limit set by this register is reached, the modem hangs up. Raising this limit may be necessary if, for example, telephone lines are extremely noisy. The Re-transmission delays may be undesirable, but the modem will not hang up. The range of this register is 0-255, with a factory setting of 100.

**Glossary**
Analog Signals	A continuously varying waveform measured with respect to a reference such as ground. A voice is transmitted over a conventional telephone line as an analog signal.
ANALOOP	Analog Loopback (see Analog Loopback)
Analog Loopback	Amethod of testing a modem by disconnecting it from the telephone line and connecting its transmit output to its receive input. This procedure aids in testing the functioning of the modem, and it also helps distinguish between the modem and the telephone line as the source of a problem.
Algorithm	Such as DSP algorithm, is the specific strategy or procedure used in formulating a solution as in echo cancellation algorithms used in the Electrical Echo Cancellation training of a telephone line for use in a speakerphone environment.
Asynchronous	Asynchronous transmission, “character asynchronous”, sends one character block at a time adding a start bit and a stop bit to re-synchronize the receiver to the next character, as the time frame between characters is not uniform and not related to the clock.
AT prefix	Attention signal, all commands, except the A/ command, must be preceded with the AT characters. They must be entered as all upper case or all lower case.
Baud	A unit of measure for the modulation rate of a modem. Baud measures the rate at which signals on the transmission medium change. Some modem speeds represent more than one information bit per baud. For instance, a V.22bis modem uses 4 bits per baud and therefore transmits 2400 bits per second using a 600 baud modulation rate.
Bit	The smallest unit of data and the basic unit in data communications. A bit represents a logical state of zero (space) and one (mark).
BPS (bits per second)	A measure of the data transfer rate represented in binary code.
Buffer	A temporary memory location which stores data until an acknowledgment occurs from the receiving modem to prevent loss of data due to differences in the rate of data flow when transmitting or receiv-ing data.
Break Handling	Determines the optional choices the modem takes when responding to a break signal, usually recognized by an extended space signal for a specific amount of time, received from the DTE or keyboard Break or (CTRL) C keys. The Break Handling is controlled by the \K command.
CCITT	Consultative Committee for International Telephone and Telegraph: Part of the ITU (International Telecommunication Union), a United Nations Agency. This agency has been recently renamed the International Telecommunications Union-Telecommunications Standards Sector (ITU-TSS).
Command line	The set of characters, beginning with AT, that are typed and sent to the modem, are referred to as a command line. A command line can contain one AT command or a series of AT commands but cannot exceed 64 characters in length.
Carriage return	Except for the A/ command and the escape command, “+++”, all command lines must end with a carriage return <CR>. The modem will not execute the commands on the command line until it receives a <CR>.
Command buffer	The command buffer holds the modem commands before they are executed. The command buffer can hold up to 64 characters, excluding AT and <CR>. If more than 64 charac-ters are typed, the modem will send an ERROR response and will not execute the command line.
Command Mode	The modem must be in the command mode before commands are typed. The modem enters the command mode when it is turned on or reset, when it loses a connection or when it is in the data mode and the escape sequence (+++) is entered. When the modem is in the command mode it will ac-cept instructions, in the form of commands, from the DTE or Personal Computer, then returns re-sponses in either numeric (terse) or word (verbose) format. The command mode allows the modem to be configured for a particular application (e.g. data, fax) or to perform a function (e.g. originate or answer a call).
CTS - Clear to Send	The Clear to Send control signal on the RS232 indicates that the modem has received a carrier tone and is ready to modulate data. CTS is typically used in conjunction with the RTS (Request to Send) signal to set up a two way flow control between modem and DTE.
Data Compression	Data compression is a method of increasing data throughput in a reduced amount of time. Each compressed character may represent more than one data character. An example, is a technique where transferred data is examined for repeating data. The repetitive characters are replaced by a character count or a unique code. The receiving modem then reconstructs the data to its original form.
Data Mode	The modem is in the data mode after it makes a connection with a remote modem and sends the appropriate CONNECT response. Everything it receives from the DTE is considered data that it then sends over the telephone line to the remote modem.
DCD - Data Carrier Detect	The DCD signal indicates to the terminal device that the modem is receiving a carrier signal from a remote modem.
DCE - Data Communications Equipment	The DCE is the local or remote modem device usually connected to the DTE.
Dry Transformer	The present Sierra V.34 modem chip set application schematics recommend the use of a “dry” type transformer for best performance. Dry transformers require the use of DC blocking capacitors (AC coupled) to eliminate any DC current flow in either primary or secondary. Dry transformers require the use of a line holding current circuit to pass the holding current instead of through the transformer. Dry transformers typically achieve better return loss figures than wet transformers due to higher primary inductance that is more consistent with frequency.
DSR - Data Set Ready	The RS232 signal indicating the modem is connected and ready to transmit data.
DTE - Data Terminal Equipment	The DTE is the local or remote computer or terminal equipment.
DTMF	Dual Tone Multi-Frequency: DTMF is used in (push button) tone dialing. A DTMF tone is made up of two tones, one high frequency and one low frequency. The telephone can normally dial 12 dif-ferent DTMF tones, 1-9, 0, *, and #. Four additional tones: A, B, C, and D are also available in mo-dem dialing.
DTR	Data Terminal Ready: The DTR signal on the RS232 interface indicates to the modem that the DTE is ready to receive data.
Editing a command	The command line can be edited before entering a carriage return, by using the backspace key to delete characters. The backspace key can be used to delete every character except the AT. If the keyboard does not have a backspace key, Control-H can be used.
EIA	Electronics Industry Association: The EIA is made up of a (North American) national body which sets electronics industry standards for U.S. electronics manufacturers.
Error Control	Data checking techniques which check for error free transmission through the monitoring of the reliability and accuracy of characters or blocks of data sent over a telecommunication line. Error Control Protocols such as MNP 4 and V.42 are two schemes that provide error correction.
Escape characters	Sierra modem control firmware can be assembled to support either Time Independent Escape Sequence (T.I.E.S.) or the alternate patented Hayes time dependent escape se-quence, to switch the modem from the data mode. The escape characters can be changed from the default characters, “+++”, using S-Register 2 (S2).
ITU-T	International Telecommunications Union - Telecommunication Sector: ITU-T replaces CCITT, as the leading telecommunications standards organization. ITU-T defines standards for telegraphic and telephone equipment, sets of telecommunications protocols and interfaces such as the V series CCITT recommendations.
MNP	Microcom Networking Protocol: MNP is an error correcting and proprietary data compression protocol, covering dial up modems from 2400 to 33.6Kbps. MNP offers a reliable and widely accepted method of correcting data errors in transmissions over dial up transmission lines. MNP error control classes 2, 3 and 4, along with LAPM protocol are mandatory elements of the CCITT recommendation - V.42. MNP data compression classes 5 through 7, are a set of proprietary protocols that are licensed from Microcom which can compress files up to 3:1, or up to a 300% speed improvement.
NV	NV is an abbreviation for Non-Volatile, as in memory which is not lost when the power to the IC is shut off or removed. Usually refers to the EEPROM on the modem PCB which contains the modem’s configuration parameters and stored phone numbers. On newer PnP (plug and play) PCB’s, the PnP EEPROM stores the modem’s resource configuration data file, including a PCB serial number.
LAPM	Link Access Procedure for Modems: LAPM is part of V.42 recommendation for modem error con-trol. LAPM is based on HDLC, a bit oriented protocol developed by the International Standards Organization. HDLC is a bit oriented communications protocol which uses control codes of differing bit pattern and positions. The bit patterns differ dramatically from data patterns, thereby re-ducing errors when used together.
Readability	The command line can be made more readable by including spaces between commands. The spaces do not count towards the 64 character limit, except in fax mode.
Responses	The modem sends responses when it executes a command line. Responses take the form of words or numbers depending on the setting of the V command. If a V command is not specified, the default (V1) word responses will respond to the AT Commands.
RTS	Request to Send: The RS232 control signal which puts the modem in the originate mode and prepares it to send data upon receipt of a CTS signal from the terminal.
Trellis Coding	Sierra high speed modems use Trellis coding as a method of improving noise immunity using a convolutional encoder to select a sequence of subsets in a partitioned signal constel-lation. Trellis coding is a method of forward error correction where each signal element is given a coded binary value portraying its phase and amplitude. Compared to the preceding signal, the receiv-ing modem determines errors.
UART	Universal Asynchronous Receiver / Transmitter: The UART performs the parallel to serial con-version of digital data to be transmitted and the serial to parallel conversion of data that has been transmitted.
V.13	ITU-T standard for simulated carrier control. V.13 allows a full duplex modem to be used to emulate a half duplex modem.
V.14	ITU-T standard for asynchronous to synchronous conversion without error control. V.14 actually allows a synchronous modem to carry start / stop (async) characters. A V.42 modem connecting with a modem that does not have error control falls back to V.14 operation to work without error control.
V.34	ITU-T modem standard for operating on GSTNs at data signaling rates of 33.6Kbps to 2400bps. V.34 uses channel separation by echo cancellation techniques and quadrature amplitude modulation for each channel and trellis coding for all data signaling rates.
V.42	See MNP, Error Control.
V.42 bis	V.42 bis is an ITU-T data compression standard. It can achieve compression ratios up to 4:1(on compressible files), or 115,200bps on a 28,800bps modem. V.42 bis 400% compression is based on the Lempel Ziv data compression model which reduces the number of bits to transfer.

Glossary

Analog Signals

A continuously varying waveform measured with respect to a reference such as ground. A voice is transmitted over a conventional telephone line as an analog signal.

ANALOOP

Analog Loopback (see Analog Loopback)

Analog Loopback

Amethod of testing a modem by disconnecting it from the telephone line and connecting its transmit output to its receive input. This procedure aids in testing the functioning of the modem, and it also helps distinguish between the modem and the telephone line as the source of a problem.

Algorithm

Such as DSP algorithm, is the specific strategy or procedure used in formulating a solution as in echo cancellation algorithms used in the Electrical Echo Cancellation training of a telephone line for use in a speakerphone environment.

Asynchronous

Asynchronous transmission, “character asynchronous”, sends one character block at a time adding a start bit and a stop bit to re-synchronize the receiver to the next character, as the time frame between characters is not uniform and not related to the clock.

AT prefix

Attention signal, all commands, except the A/ command, must be preceded with the AT characters. They must be entered as all upper case or all lower case.

Baud

A unit of measure for the modulation rate of a modem. Baud measures the rate at which signals on the transmission medium change. Some modem speeds represent more than one information bit per baud. For instance, a V.22bis modem uses 4 bits per baud and therefore transmits 2400 bits per second using a 600 baud modulation rate.

Bit

The smallest unit of data and the basic unit in data communications. A bit represents a logical state of zero (space) and one (mark).

BPS (bits per second)

A measure of the data transfer rate represented in binary code.

Buffer

A temporary memory location which stores data until an acknowledgment occurs from the receiving modem to prevent loss of data due to differences in the rate of data flow when transmitting or receiv-ing data.

Break Handling

Determines the optional choices the modem takes when responding to a break signal, usually recognized by an extended space signal for a specific amount of time, received from the DTE or keyboard Break or (CTRL) C keys. The Break Handling is controlled by the \K command.

CCITT

Consultative Committee for International Telephone and Telegraph: Part of the ITU (International Telecommunication Union), a United Nations Agency. This agency has been recently renamed the International Telecommunications Union-Telecommunications Standards Sector (ITU-TSS).

Command line

The set of characters, beginning with AT, that are typed and sent to the modem, are referred to as a command line. A command line can contain one AT command or a series of AT commands but cannot exceed 64 characters in length.

Carriage return

Except for the A/ command and the escape command, “+++”, all command lines must end with a carriage return <CR>. The modem will not execute the commands on the command line until it receives a <CR>.

Command buffer

The command buffer holds the modem commands before they are executed. The command buffer can hold up to 64 characters, excluding AT and <CR>. If more than 64 charac-ters are typed, the modem will send an ERROR response and will not execute the command line.

Command Mode

The modem must be in the command mode before commands are typed. The modem enters the command mode when it is turned on or reset, when it loses a connection or when it is in the data mode and the escape sequence (+++) is entered. When the modem is in the command mode it will ac-cept instructions, in the form of commands, from the DTE or Personal Computer, then returns re-sponses in either numeric (terse) or word (verbose) format. The command mode allows the modem to be configured for a particular application (e.g. data, fax) or to perform a function (e.g. originate or answer a call).

CTS - Clear to Send

The Clear to Send control signal on the RS232 indicates that the modem has received a carrier tone and is ready to modulate data. CTS is typically used in conjunction with the RTS (Request to Send) signal to set up a two way flow control between modem and DTE.

Data Compression

Data compression is a method of increasing data throughput in a reduced amount of time. Each compressed character may represent more than one data character. An example, is a technique where transferred data is examined for repeating data. The repetitive characters are replaced by a character count or a unique code. The receiving modem then reconstructs the data to its original form.

Data Mode

The modem is in the data mode after it makes a connection with a remote modem and sends the appropriate CONNECT response. Everything it receives from the DTE is considered data that it then sends over the telephone line to the remote modem.

DCD -
Data Carrier Detect

The DCD signal indicates to the terminal device that the modem is receiving a carrier signal from a remote modem.

DCE -
Data Communications Equipment

The DCE is the local or remote modem device usually connected to the DTE.

Dry Transformer

The present Sierra V.34 modem chip set application schematics recommend the use of a “dry” type transformer for best performance. Dry transformers require the use of DC blocking capacitors (AC coupled) to eliminate any DC current flow in either primary or secondary. Dry transformers require the use of a line holding current circuit to pass the holding current instead of through the transformer. Dry transformers typically achieve better return loss figures than wet transformers due to higher primary inductance that is more consistent with frequency.

DSR - Data Set Ready

The RS232 signal indicating the modem is connected and ready to transmit data.

DTE -
Data Terminal Equipment

The DTE is the local or remote computer or terminal equipment.

DTMF

Dual Tone Multi-Frequency: DTMF is used in (push button) tone dialing. A DTMF tone is made up of two tones, one high frequency and one low frequency. The telephone can normally dial 12 dif-ferent DTMF tones, 1-9, 0, *, and #. Four additional tones: A, B, C, and D are also available in mo-dem dialing.

DTR

Data Terminal Ready: The DTR signal on the RS232 interface indicates to the modem that the DTE is ready to receive data.

Editing a command

The command line can be edited before entering a carriage return, by using the backspace key to delete characters. The backspace key can be used to delete every character except the AT. If the keyboard does not have a backspace key, Control-H can be used.

EIA

Electronics Industry Association: The EIA is made up of a (North American) national body which sets electronics industry standards for U.S. electronics manufacturers.

Error Control

Data checking techniques which check for error free transmission through the monitoring of the reliability and accuracy of characters or blocks of data sent over a telecommunication line. Error Control Protocols such as MNP 4 and V.42 are two schemes that provide error correction.

Escape characters

Sierra modem control firmware can be assembled to support either Time Independent Escape Sequence (T.I.E.S.) or the alternate patented Hayes time dependent escape se-quence, to switch the modem from the data mode. The escape characters can be changed from the default characters, “+++”, using S-Register 2 (S2).

ITU-T

International Telecommunications Union - Telecommunication Sector: ITU-T replaces CCITT, as the leading telecommunications standards organization. ITU-T defines standards for telegraphic and telephone equipment, sets of telecommunications protocols and interfaces such as the V series CCITT recommendations.

MNP

Microcom Networking Protocol: MNP is an error correcting and proprietary data compression protocol, covering dial up modems from 2400 to 33.6Kbps. MNP offers a reliable and widely accepted method of correcting data errors in transmissions over dial up transmission lines. MNP error control classes 2, 3 and 4, along with LAPM protocol are mandatory elements of the CCITT recommendation - V.42. MNP data compression classes 5 through 7, are a set of proprietary protocols that are licensed from Microcom which can compress files up to 3:1, or up to a 300% speed improvement.

NV

NV is an abbreviation for Non-Volatile, as in memory which is not lost when the power to the IC is shut off or removed. Usually refers to the EEPROM on the modem PCB which contains the modem’s configuration parameters and stored phone numbers. On newer PnP (plug and play) PCB’s, the PnP EEPROM stores the modem’s resource configuration data file, including a PCB serial number.

LAPM

Link Access Procedure for Modems: LAPM is part of V.42 recommendation for modem error con-trol. LAPM is based on HDLC, a bit oriented protocol developed by the International Standards Organization. HDLC is a bit oriented communications protocol which uses control codes of differing bit pattern and positions. The bit patterns differ dramatically from data patterns, thereby re-ducing errors when used together.

Readability

The command line can be made more readable by including spaces between commands. The spaces do not count towards the 64 character limit, except in fax mode.

Responses

The modem sends responses when it executes a command line. Responses take the form of words or numbers depending on the setting of the V command. If a V command is not specified, the default (V1) word responses will respond to the AT Commands.

RTS

Request to Send: The RS232 control signal which puts the modem in the originate mode and prepares it to send data upon receipt of a CTS signal from the terminal.

Trellis Coding

Sierra high speed modems use Trellis coding as a method of improving noise immunity using a convolutional encoder to select a sequence of subsets in a partitioned signal constel-lation. Trellis coding is a method of forward error correction where each signal element is given a coded binary value portraying its phase and amplitude. Compared to the preceding signal, the receiv-ing modem determines errors.

UART

Universal Asynchronous Receiver / Transmitter: The UART performs the parallel to serial con-version of digital data to be transmitted and the serial to parallel conversion of data that has been transmitted.

V.13

ITU-T standard for simulated carrier control. V.13 allows a full duplex modem to be used to emulate a half duplex modem.

V.14

ITU-T standard for asynchronous to synchronous conversion without error control. V.14 actually allows a synchronous modem to carry start / stop (async) characters. A V.42 modem connecting with a modem that does not have error control falls back to V.14 operation to work without error control.

V.34

ITU-T modem standard for operating on GSTNs at data signaling rates of 33.6Kbps to 2400bps. V.34 uses channel separation by echo cancellation techniques and quadrature amplitude modulation for each channel and trellis coding for all data signaling rates.

V.42

See MNP, Error Control.

V.42 bis

V.42 bis is an ITU-T data compression standard. It can achieve compression ratios up to 4:1(on compressible files), or 115,200bps on a 28,800bps modem. V.42 bis 400% compression is based on the Lempel Ziv data compression model which reduces the number of bits to transfer.

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n	word length	parity	number of stop bits
0	6	none	1
1	7	none	1
2	7	determined by most recent \Pn command	1
3	8	none	1
4	7	determined by most recent \Pn command	2
5	8	determined by most recent \Pn command	1

Command	Function
\Cn	Fallback and Prelink Buffer Control The \Cn command determines fallback selection. If an error correcting protocol is enabled, this command also determines whether incoming data from the remote modem will be buffered while the receiving modem waits to establish the error correcting link.
\C0	Timeout and fallback; speed buffer; no data buffer.
\C1	Timeout and fallback; speed buffer; buffer receive data.
\C2	Auto reliable; fallback with fallback character speed buffer; no receive data buffer.
\C3	Timeout and fallback; ITU-T V.14; buffer receive data.
\C4	Timeout and fallback with fallback character; ITU-T V.14; no data buffer
\Gn	Normal Mode Line Flow Control The \B command sets up the character length and format the modem uses in front ends that do not send AT commands. Character format is determined by the value of n according to the following table.
\G0	Turn off port flow control.
\G1	Turn on port flow control. Use this setting if the modem is receiving data from the remote system faster than it can process
\G2	Enable in transmit path only
\G3	Enable in transmit and receive paths, with pass-through XON/XOFF signals to the DTE.
\Kn	Break Character Handling The \K command determines how the modem will react to break characters received from the DTE during an error corrected data link.
\K0	Expedite break; destroy current buffer data.
\K1	Expedite break; save current buffer data.
\K2	Timed break; save buffer data.
\K3	Ignore breaks from the DTE.
\K4	Timed break until no break character; save buffer data.
\K5	Timed break until no break character; save buffer data.
\Nn	Asynchronous Protocol The \N command controls the type of connection when asynchronous operation (&M0) is in effect. Note: n = 0 to 2 will disable V.42/V.42bis connection.
\N0	Standard operation (non-EC, buffered data).
\N1	Direct operation (non-EC, data not buffered).
\N2	Reliable MNP operation. (Attempts MNP connection; if not, then disconnects.)
\N3	Auto-reliable operation (V.42 or MNP if communicating with remote V.42 or MNP modem; otherwise, standard).
\N4	Reliable V.42 mode.
\N5	Auto-reliable V.42 or MNP mode.
\N6	Simulated controlled carrier (ITU-T V.13).
\Pn	Parity Type The \P command sets up the parity to use in data mode for systems that do not send AT commands.
\P0	Even.
\P1	Space.
\P2	Odd.
\P3	Mark.
\P4	Automatic (from last AT command).
\Qn	Modem to DTE Port Flow Control
\Q0	Disable DTE flow control, in both directions.
\Q1	Bi-directional XON/XOFF. Modem uses XOFF character to stop data from DTE and XON character to resume transmission. DTE uses XOFF to stop modem from sending data and XON to resume transmission.
\Q2	Unidirectional CTS interface signal. Modem uses CTS line to control data from DTE. DTE cannot control data from modem.
\Q3	Bi-directional RTS/CTS interface signals. Modem uses CTS line to control data from DTE. DTE uses RTS line to control data from modem.
\Q4	Unidirectional XON/XOFF flow control. Modem uses XOFF character to stop data from DTE and XON character to resume transmission. DTE cannot control data from modem.
\Tn	DTE Speed This command determines the speed at which the DTE and modem will interface.
\T0	Autobaud speed
\T1	Last AT speed
\T2	300
\T3	1,200
\T4	2,400
\T5	4,800
\T6	7,200
\T7	9,600
\T8	12,000
\T9	14,400
\T10	16,800
\T11	19,200
\T12	21,600
\T13	24,000
\T14	26,400
\T15	28,800
\T16	31,200
\T17	33,600
\T18	38,400
\T19	57,600
\T20	115,200
\T21	115,200
\T22	128,000
\Vn	Connect Message Type This command determines the type of connect message sent to the DTE upon establishing a data link.
\V0	The \V0 options the modem to send the standard Connect message upon reaching data mode plus V.42 messages after the link negotiation. The connect message displays the data signaling rate.

Command	Function
\ V3	The \V3 command sends only the connect message after the link negotiation. The mes-sage will indicate the data signaling rate for V.13 and V.14 connections and the DTE rate for all other connections.
\ V4	The \V4 command sets both the transmit data signaling rate and receive data signaling rate.

Command	Function
\V1	The \V1 delays sending the Connect message until an error corrected link has been es-tablished. The connect message indicates the DTE speed established, when it will indicate the data signaling rate. (Serial only)

Command	Function
\ V0 and \V1	With \V0 and \V1, the following connect messages are sent when link negotiation is complete

Command	Function
\ V2	The \V2 command is similar to the \V0 command except the modem adds a /REL at the end of the message when a V.42 error corrected link has been established.