Modem Control Codes

This section lists the command and control codes for popular modems. Most modems use a standard

AT command set that was developed by Hayes and augmented by U.S. Robotics. Table 27

comes in handy when you need to reconfigure a modem without the original manual. Even if

your modem is not Hayes or U.S. Robotics, it probably follows most of these commands because

this command set has become somewhat of a standard. S-register values listed at the end of the

table are also somewhat standard but are more subject to variation in the defaults by brand and

model.


Modem AT Commands and S-Register Features

Command Modem Functions and Options

&

% See Extended Command Set

A Force Answer mode when modem has not received an incoming call

A/ Reexecute last command once

A>

Any key Terminate current connection attempt; exit Repeat mode

AT Attention: must precede all other commands, except A/, A>, and +++

Bn Handshake options

B0 CCITT answer sequence

B1 Bell answer tone

Cn Transmitter On/Off

C0 Transmitter Off

C1 Transmitter On—Default

Dn Dial number n and go into originate mode

Use any of these options:

P Pulse dial—Default

T Touch-tone dial

, (Comma) Pause for two seconds

; Return to command state after dialing

“... Dial the letters that follow

! Flash switch-hook to transfer call

W Wait for second dial tone (if X3 or higher is set)

@ Wait for an answer (if X3 or higher is set)

R Reverse frequencies

S Dial stored number

DL Dial the last-dialed number

DSn Dial number stored in NVRAM at position

En Command mode local echo; not applicable after a connection has been made

E0 Echo Off

E1 Echo On

Fn Local echo On/Off when a connection has been made

F0 Echo On (Half duplex)

F1 Echo Off (Full duplex)—Default

Hn On/Off hook control

H0 Hang up (go on hook)—Default

H1 Go off hook

In Inquiry

I0 Return product code

I1 Return memory (ROM) checksum

I2 Run memory (RAM) test

I3 Return call duration/real time

I4 Return current modem settings

I5 Return NVRAM settings

I6 Return link diagnostics

I7 Return product configuration

Kn

K0 ATI3 displays call duration—Default

K1 ATI3 displays real time; set with ATI3=HH:MM:SSK1

Ln

L0 Low

L1 Low

L2 Medium

L3 High

Mn Monitor (speaker) control

M0 Speaker always Off

M1 Speaker On until carrier is established—Default

M2 Speaker always On

M3 Speaker On after last digit dialed, Off at carrier detect

O Return online after command execution

O0 Return online, normal

O1 Return online, retrain

P Pulse dial

Qn Result codes display

Q0 Result codes displayed

Q1 Result codes suppressed (quiet mode)

Q2 Quiet in answer mode only

Sr=n Set Register commands: r is any S-register; n must be a decimal number between 0 and

255.

Sr.b=n Set bit .b of register r to n (0/Off or 1/On)

Sr? Query register r

T Tone dial

Vn Verbal/Numeric result codes

V0 Numeric mode

V1 Verbal mode

Xn Result code options

Yn Long space disconnect

Y0 Disabled

Y1 Enabled; disconnects after 1 1/2-second break

Z Software reset

+++ Escape code sequence, preceded and followed by at least one second of no data

transmission

/(Slash) Pause for 125 msec

> Repeat command continuously or up to 10 dial attempts, Cancel by pressing

any key

$ Online Help—Basic command summary

&$ Online Help—Ampersand command summary

%$ Online Help—Percent command summary

D$ Online Help—Dial command summary

S$

<Ctrl>-S Stop/restart display of Help screens-C Cancel display Help screens

<Ctrl>

<Ctrl>-K Cancel display Help screens



Extended Command Set

&An

&A0 Suppress ARQ result codes

&A1 Display ARQ result codes—Default

&A2 Display HST and V.32 result codes

&A3 Display protocol result codes

&Bn Data Rate, terminal-to-modem (DTE/DCE)

&B0 DTE rate follows connection rate—Default

&B1 Fixed DTE rate

&B2 Fixed DTE rate in ARQ mode; variable DTE rate in non-ARQ mode

&Cn Carrier Detect (CD) operations

&C0 CD override

&C1 Normal CD operations

&Dn Data Terminal Ready (DTR) operations

&D0 DTR override

&D1 DTR Off; goes to command state

&D2 DTR Off; goes to command state and on hook

&D3 DTR Off; resets modem

&F Load factory settings into RAM

&Gn Guard tone

&G0 No guard tone; U.S., Canada—Default

&G1 Guard tone; some European countries

&G2 Guard tone; U.K., requires B0

&Hn Transmit Data flow control

&H0 Flow control disabled—Default

&H1 Hardware (CTS) flow control

&H2 Software (XON/XOFF) flow control

&H3 Hardware and software control

&In Received Data software flow control

&I0 Flow control disabled—Default

&I1 XON/XOFF to local modem and remote computer

&I2 XON/XOFF to local modem only

&I3 Host mode, Hewlett-Packard protocol

&I4 Terminal mode, Hewlett-Packard protocol

&I5 ARQ mode-same as &I2; non-ARQ mode; look for incoming XON/XOFF

&Jn Telephone jack selection

&J0 RJ-11/RJ-41S/RJ-45S

&J1 RJ-12/RJ-13

&Kn Data compression

&K0 Disabled

&K1 Auto enable/disable—Default

&K2

&K3 V.42bis only

&Ln

&L0 Normal phone line—Default

&L1 Leased line

&Mn Error Control/Synchronous Options

&M0 Normal mode, no error control

&M1 Sync mode

&M2 Sync mode 2—stored number dialing

&M3 Sync mode 3—manual dialing

&M4 Normal/ARQ mode—Normal if ARQ connection cannot be made—Default

&M5 ARQ mode—hang up if ARQ connection cannot be made

&Nn Data Rate, data link (DCE/DCE)

&N0 Normal link operations—Default

&N1 300bps

&N2 1,200bps

&N3 2,400bps

&N4 4,800bps

&N5 7,200bps

&N6 9,600bps

&N7 12Kbps

&N8 14.4Kbps

&Pn Pulse dial make/break ratio

&P0 North America—Default

&P1 British Commonwealth

&RnNormal/Leased line operationEnabledARQ result codes 14–17, 19Online Help—S-register summaryLoudness of speaker volumeModem clock operationRepeat last command continuouslySee Extended Command Set