Multi-Tech Systems MT2834MR6 User Manual

MultiModem

MT2834MR6

User Guide

MultiModem MT2834MR6 User Guide
PN: S000326A

Copyright ©2003 by Multi-Tech Systems, Inc.
All rights reserved. This publication may not be reproduced, in whole or in part, without prior written permission from Multi-

Tech Systems, Inc.
Multi-Tech Systems, Inc. makes no representations or warranties with respect to the contents hereof and specifically

disclaims any implied warranties of merchantability or fitness for any particular purpose. Furthermore, Multi-Tech
Systems, Inc. reserves the right to revise this publication and to make changes from time to time in the content hereof
without obligation of Multi-Tech Systems, Inc. to notify any person or organization of such revisions or changes.

Revision Date Description

A 12/30/2003 Initial release of MT2834MR6 User Manual on CD.

Trademarks

Trademarks of Multi-Tech Systems, Inc. are as follows: MultiExpress, MultiExpressFax, MultiModemII, Multi-Tech and the
Multi-Tech logo. Windows is a registered trademark of Microsoft Corporation.

Technical Support

France [e-mail] [phone]
India [e-mail] [phone]
U.K. [e-mail] [phone]
U.S., Canada [e-mail] [phone]
Rest of World [e-mail] [phone]

World Headquarters

Multi-Tech Systems, Inc.
2205 Woodale Drive
Mounds View, Minnesota 55112 U.S.A.
[phone] or [phone]
U.S. FAX [phone]
Technical Support [phone]
www.multitech.com

Contents

Chapter 1 - Introduction..................................................................................... 7

1.1 Introduction ............................................................................................. 8

1.2 Manual Organization...............................................................................8

1.3 Description ............................................................................................. 9

1.4 FCC Regulations for Telephone Line Interconnection........................... 10

1.4.1 FCC Fax Update ................................................................................. 10

1.5 Canadian Limitations Notice................................................................. 1 1

1.6 Technical Specifications ....................................................................... 12

1.7 Power Supply ....................................................................................... 14

1.8 Modem LED Indicators ......................................................................... 15

1.9 Busy Switch ......................................................................................... 15

1.10 MT2834MR6 Installation Notes ............................................................. 16

1.11 Safety Warnings ................................................................................... 16

Chapter 2 - Dialing and Answering ................................................................. 17

2.1 Introduction ........................................................................................... 18

2.2 Dial-Up Automatic Answering ............................................................... 18

2.3 Dial-Up Handshaking Details................................................................ 18

2.4 Call T ermination.................................................................................... 19

Chapter 3 - AT Commands .............................................................................. 20

3.1 Working with AT Commands................................................................ 21

3.1.1 Modes of Operation ............................................................................ 21

3.2.2 Command Structure............................................................................2 2

3.3.3 Command Editing ............................................................................... 22

3.2 Dialing Commands ............................................................................... 26

3.3 Dial Modifier Commands ...................................................................... 27

3.4 Phone Number Memory Commands.................................................... 30

3.5 Configuration Storage and Recall Commands..................................... 32

3.6 Modem Response (Result Code) Commands..................................... 34

3.7 Online Connection Commands ............................................................ 36

3.8 V.34 Commands................................................................................... 40

3.9 RS-232 Interface Commands .............................................................. 41

3.10 Error Correction and Data Compression Commands .......................... 43

3.11 Speed Conversion Commands ............................................................ 45

3.12 Immediate Action Commands .............................................................. 47

3.12 Flow Control Commands ..................................................................... 49

3.13 Escape Sequences.............................................................................. 52

3.14 Remote Configuration Commands ....................................................... 53

3.15 Line Probe Commands ........................................................................ 54

3.16 Diagnostic Commands ......................................................................... 55

Chapter 4 - S-Registers.................................................................................... 56

4.1 Introduction ........................................................................................... 57

4.2 S-Registers .......................................................................................... 57

4.3 Reading and Assigning S-Register Values ........................................... 63

4.3.1 Examples of Assigning Values ...........................................................63

4.3.2 Examples of Reading Values..............................................................63

4.4 AT Commands Affecting S-Registers................................................... 64

Chapter 5 - Error Correction, Data Compression & Speed Conversion..... 65

5.1 Introduction ........................................................................................... 66

5.2 How V.42 Detects and Corrects Errors ................................................ 67

5.3 Data Compression ............................................................................... 68

5.4 MNP Classes........................................................................................ 68

5.5 V.42 Mode Select Command (#L)......................................................... 69

5.5.1 #L0 Command..................................................................................... 69

5.5.1.1 Originate Mode ................................................................................69

5.5.1.2 Answer Mode...................................................................................6 9

5.5.2 #L1 Command..................................................................................... 69

5.5.3 #L2 Command ....................................................................................69

5.5.4 #L3 Command..................................................................................... 69

5.6 Modes of Operation .............................................................................. 70

5.6.1 Non-Error Correction Mode (&E0)........................................................70

5.6.2 Reliable Mode (&E2) ........................................................................... 70

5.6.3 Autoreliable Mode (&E1) .....................................................................70

5.7 Flow Control ......................................................................................... 71

5.8 Modem-Initiated Flow Control ............................................................... 72

5.8.1 XON/XOFF Flow Control (&E5)........................................................... 72

5.8.2 Hardware Flow Control (&E4) ..............................................................7 2

5.9 Pacing (&E13) ...................................................................................... 73

5.9.1 XON/XOFF Pass-Through (&E7) ........................................................ 73

5.9.2 Non-Error Correction Mode Flow Control (&E10 and &E11).................7 3

5.9.3 Hewlett Packard ENQ/ACK Pacing (&E9)...........................................7 3

5.10 Compression, Error Correction, Flow Control,

and Pacing Commands ........................................................................ 74

5.10.1 V.42 Error Correction Modes ..............................................................74

5.10.2 Modem-Initiated Flow Control ............................................................. 74

5.10.3 XON/XOFF Pass-Through ..................................................................74

5.10.4 Hewlett Packard ENQ/ACK Pacing.....................................................74

5.10.5 Non-Error Correction Mode Flow Control ............................................. 74

5.10.6 Pacing (Computer-Initiated Flow Control)............................................ 74

5.10.7 Data Compression ..............................................................................74

5.11 Result Codes ........................................................................................ 75

5.11.1 MNP Error Correction.......................................................................... 75

5.11.2 LAP-M Error Correction....................................................................... 75

5.11.3 Data Compression ..............................................................................75

5.12 Speed Conversion ................................................................................ 75

5.12.1 Baud Adjust ($BA) .............................................................................. 76

5.12.2 Modem Baud Rate ($MB)....................................................................76

5.12.3 Serial Port Baud Rate ($SB) ............................................................... 77

5.13 Related Commands ............................................................................. 78

5.13.1 Autoreliable Buffering ($A) ..................................................................78

5.13.2 Maximum Block Size (&BS) ...............................................................7 8

5.13.3 Autoreliable Fallback Character ($F) ................................................... 78

5.13.4 Retransmit Count ($R) ........................................................................ 79

5.13.5 V.42 Error Correction at 300 bps ($E) ................................................. 79

5.14 Summary.............................................................................................. 79

Chapter 6 - Testing & Troubleshooting.......................................................... 80

6.1 Introduction ........................................................................................... 81

6.2 Local Analog Loopback Test (V .54 Loop 3)........................................... 82

6.2.1 Test Procedure ...................................................................................82

6.3 Remote Digital Loopback Test (V.54 Loop 2)........................................ 83

6.3.1 Test Procedure ...................................................................................83

6.4 Local Digital Loopback Test (V.54 Loop 2)............................................ 84

6.4.1 Test Procedure ...................................................................................84

Chapter 7 - Warranty & Service....................................................................... 85

7.1 Multi-Tech Systems, Inc. Warranty & Repairs Policies......................... 86

7.1.1 Warranty ............................................................................................. 86

7.1.2 U.S. and Canadian Customers............................................................86

7.1.3 International Customers (outside U.S.A. and Canada)........................87

7.1.4 International Distributors.....................................................................8 7

7.2 Repairs................................................................................................. 88

7.2.1 Repair Procedures for U.S. and Canadian Customers ........................ 88

7.2.2 Repair Procedures for International Customers...................................88

7.2.3 Repair Procedures for International Distributors..................................89

7.2.4 Replacement Parts .............................................................................89

7.3 Technical Support ................................................................................. 89

7.4 Internet Site .......................................................................................... 89

Appendices........................................................................................................ 90

Appendix A..................................................................................................... 91

ASCII Conversion Chart...................................................................................91

Appendix B .................................................................................................... 92

Dial Pulses ...................................................................................................... 92

Tone Dial Frequencies ..................................................................................... 93

Appendix C .................................................................................................... 94

Result Code Summary..................................................................................... 94

Appendix D .................................................................................................... 96

S-Register Summary ....................................................................................... 96

Appendix E .................................................................................................... 98

AT Command Summary .................................................................................. 98

Appendix F................................................................................................... 106

RS-232C Interface Specifications..................................................................10 6

Functional Description of the RS-232C Signals ............................................. 10 7

Transmitted Data (TD) — Pin 2 ......................................................................10 7

Received Data (RD) — Pin 3.......................................................................... 10 7

Request To Send (RTS) — Pin 4.................................................................... 10 7

Clear To Send (CTS) — Pin 5......................................................................... 107

Data Set Ready (DSR) — Pin 6 ..................................................................... 107

Signal Ground (SG) — Pin 7 ..........................................................................10 7

Carrier Detect (CD) — Pin 8 ........................................................................... 107

Test Voltage (+V) — Pin 9 .............................................................................. 108

High Speed (HS) — Pin 12.............................................................................10 8

Transmit Clock (TC) — Pin 15........................................................................ 108

Receive Clock (RC) — Pin 17 ........................................................................ 108

Data Terminal Ready (DTR) — Pin 20 ............................................................10 8

Ring Indicator (RI) — Pin 22 .......................................................................... 10 9

External Transmit Clock (XTC) — Pin 24........................................................10 9

Terminal Busy (OOS) — Pin 25...................................................................... 10 9

Appendix G .................................................................................................. 110

Cable and Connector Diagrams ..................................................................... 110

APPENDIX H ................................................................................................111

Introduction to MultiTech Escape Methods ................................................... 111

How to Select an Escape Method..................................................................11 2

Escape Method 1: +++AT<CR> ..................................................................... 112

Escape Method 2: <BREAK>AT<CR> ........................................................... 112

S-Registers and Escape Sequence ...............................................................11 3

Aborting an Escape Sequence ...................................................................... 11 3

APPENDIX I................................................................................................. 1 14

Introduction to Remote Configuration............................................................. 114

Basic Procedure ............................................................................................ 1 14

Setup 11 4

Changing the Passwords ............................................................................... 11 5

Changing the Remote Escape Character ....................................................... 11 5

Index................................................................................................................. 116

Chapter 1 - Introduction

Chapter 1 - Introduction

1.1 Introduction

Welcome to the world of data communications. You have acquired one of the finest rack-mount intelligent
modems available, the MT2834MR6, from Multi-Tech Systems. This owner’s manual will help you install,
configure, test, and use your modem.

Your MT2834MR6 is designed to operate as an enhanced ITU-T V.34 dial-up modem. As such, it includes
the advanced features of Multi-Tech standalone modems, such as the popular MultiModemZDXb.

This manual documents all of the MT2834MR6’s features and capabilities, such as autodial, autoanswer,
auto-fallback, number linking, option switches, phone number memory, call progress detection, and more.
The next section will show you how to use this manual. The contents of each chapter are described, so you
will know where to turn for specific information.

1.2 Manual Organization

Chapter 1 Introduction and Description
This chapter describes the MT2834MR6 and its LED indicators, gives its technical specifications, and
provides a guide to the organization of the manual.

Chapter 2 Dialing and Answering
This chapter describes answer mode operation in detail, including handshaking procedures between two
modems and an autoanswer application. Various methods of call termination are also described.

Chapter 3 Command Mode Operation
This chapter provides an introduction to MT2834MR6 command mode fundamentals, followed by a detailed
explanation of each AT command, providing examples where applicable.

Chapter 4 S-Registers
This chapter describes the MT2834MR6’s S-registers, which are used to store various modem options. Each
S-register is defined and explained.

Chapter 5 Error Correction, Data Compression and Speed Conversion
This chapter provides detailed information about some of the advanced features of the MT2834MR6, namely,
V.42 error correction, data compression, speed conversion, and other features that improve throughput.

Chapter 6 Testing the MT2834MR6
This chapter describes loopback testing for the MT2834MR6.

Chapter 7- Warranty, Service, and Technical Support
This chapter provides the terms of the MT2834MR6’s warranty, instructions for obtaining factory service, and
information about Multi-Tech’s BBS and technical support. Information on upgrading the MT2834MR6’s
firmware is also provided.

Appendices
This chapter includes sections pertaining to ASCII/HEX/Decimal Conversion Chart, Dial Pulses and Tone
Dial Frequencies, Result Code Summary, S-Register Summary, AT Command Summary, RS-232 Interface
Specifications, Cable and Connector Diagrams, Escape Methods, and Remote Configuration.

8

Chapter 1 - Introduction

1.3 Description

Each MT2834MR6 card contains six integrated 33,600 bps MultiModems. Each modem on the MT2834MR6
card can be configured independently of the others via the MultiModemManager controller card (Model
MR4800 or MR4800E), which can support and control up to 16 MultiModem cards per rack. Refer to your
MultiModemManager

Perhaps the most significant extras incorporated in the MT2834MR6 are its V.42 error correction and V.42bis
data compression features. With error correction and data compression, transmission errors are eliminated
while increasing the modem’s throughput by a ratio of up to 4:1, for an effective overall transmission rate
approaching 115,200 bps.

The MT2834MR6 offers interactive automatic dialing capability, as well as command mode option
configuration. Two dial command strings, of up to 60 digits each, can be stored in each modem’s nonvolatile
memory. The modem supports both pulse and tone dialing, and can recognize dial tones and busy signals
for reliable call-progress detection.

The MT2834MR6 is registered by the FCC for direct connection to the public telephone networks. No Data
Access Arrangements (DAAs) are required.

The MT2834MR6 is fully compatible with the standard AT command set, and is therefore compatible with all
popular communications software packages.

Owner’s Manual

for more information about the rack and its components.

9

Chapter 1 - Introduction

1.4 FCC Regulations for Telephone Line Interconnection

1. No repairs are to be made by you. Repairs are to be made only by Multi-Tech Systems or its licensees.
Unauthorized repairs void registration and warranty. Contact Multi-Tech Systems, Inc. for details of how
to have repairs made.

2. When trouble is experienced, you must disconnect your modem from the telephone company’s jack to
determine the cause of the trouble, and reconnect your modem only when the trouble is corrected.

3. The modem cannot be connected to pay telephones or party lines.

4. If requested by the telephone company, you must notify them of the following before the MT2834MR6 is
installed:

a. The particular phone line (phone number) to which the connection is to be made.
b. The FCC Registration Number: AU7USA-30805-MM-E
c. The Ringer Equivalence: 0.3B
d. Modems can only be connected to the phone lines through standard modular jacks. The

Uniform Service Order Code (U.S.O.C.) for the standard modular jack which connect the modem
to the phone lines are: RJ-11C or RJ-11W (single line)

e. The manufacturer’s name and model number: Multi-Tech Systems - Model MT2834MR6

5. If the telephone company notifies you that your device is causing harm, unplug it. The telephone
company may disconnect your service if necessary and also may change its facilities, equipment,
operations or procedures which may affect operation of your equipment. Where practical, the telephone
company must promptly inform you in writing of the temporary disconnect or change in service, give you
the opportunity to make changes allowing uninterrupted service, and inform you of your rights to bring a
complaint to the FCC.

1.4.1 FCC Fax Update

The Telephone Consumer Protection Act of 1991 makes it unlawful for any person to use a computer or other
electronic device to send any message via a telephone fax machine unless such message clearly contains in
a margin at the top or bottom of each page or the first page of the transmission, the date and time it is sent
and an identification of the business or other entity, or other individual sending the message and the
telephone number of the sending machine or such business, other entity, or individual.

See your fax software manual for setup details.

10

Chapter 1 - Introduction

1.5 Canadian Limitations Notice

Notice: The ringer equivalence number (REN) assigned to each terminal device provides an indication of the

maximum number of terminals allowed to be connected to a telephone interface. The termination of a
interface may consist of any combination of devices subject only to the requirement that the sum of the ringer
equivalence numbers of all the devices does not exceed 5.

Notice: The Industry Canada label identifies certificated equipment. This certification means that the
equipment meets certain telecommunications network protective, operational and safety requirements.
Industry Canada does not guarantee the equipment will operate to the user’s satisfaction.

Before installing this equipment, users should ensure that it is permissible to be connected to the facilities of
the local telecommunications company. The equipment must also be installed using an acceptable method of
connection. The customer should be aware that compliance with the above conditions may not prevent
degradation of service in some situations.

Repairs to certified equipment should be made by an authorized Canadian maintenance facility designated
by the supplier. Any repairs or alterations made by the user to this equipment, or equipment malfunctions,
may give the telecommunications company cause to request the user to disconnect the equipment.

Users should ensure for their own protection that the electrical ground connections of the power utility,
telephone lines and internal metallic water pipe system, if present, are connected together. This precaution
may be particularly important in rural areas.

Caution: Users should not attempt to make such connections themselves, but should contact the appropriate
electric inspection authority, or electrician, as appropriate.

Industry Canada Certification Number:
Ringer Equivalence Number (REN): 0.2

11

Chapter 1 - Introduction

1.6 Technical Specifications

Model Number MT2834MR6
Data Rates (Modem) Six independent modems (Modem A, B, C, D, E, F), each operating at 33,600,

31,200, 28,800, 26,400, 24,000, 21,600, 19,200, 16,800, 14,400, 12,000, 9600,
4800, 2400, 1200, or 0-300 bps

Data Rates (Fax) 14,400, 9600, 4800, and 2400 bps
Data Format (Modem) Serial, binary, asynchronous at all data rates
Configuration Each of the card’s six modems is independently configurable
Compatibility (Modem) ITU-T V.42bis, V.42, V.34, AT&T V.32terbo, ITU-T V.32bis, V.32, V.25bis, V.21,

V.22bis, V.22, V.23, V.17, Bell 212A* and 103/113*

Compatibility (Fax) ITU-T Group 3, T.4, T.30, V.21, V.27ter, V.29, V.17, and EIA TR29.2
Error Correction ITU-T V.42 (MNP® Classes 3 and 4, and LAP-M)
Data Compression ITU-T V.42bis (4:1 throughput) or MNP 5 (2:1 throughput)
Speed Conversion Serial port data rates adjustable to 300, 1200, 2400, 4800,9600, 19,200, 38,400,

57,600, and 115,200 bps

Flow Control XON/XOFF, CTS/RTS, ENQ/ACK
Mode of Operation Half or full duplex over dial-up lines; automatic or manual dialing, automatic or

manual answer

Intelligent Features Fully AT command compatible; autodial; redial; repeat dial*; dial linking*; pulse or

tone dial; dial pauses; call status display; auto-parity and data rate selection;
keyboard-controlled modem options; nonvolatile memory; on-screen displays of
modem parameters, stored telephone numbers, and help menus; and remote
configuration.

AT Commands 100% compatible with standard AT command set
Command Buffer 60 characters
Automatic Dialing Standard AT command asynchronous dialing
Modem Modulations FSK at 300 bps, PSK at 1200 bps, QAM at 2400, 4800, and 9600 bps (non-trellis),

QAM with trellis-coded modulation (TCM) at 9600, 12,000, 14,400, 16,800, 19,200,
21,600, 24,000, 26,400, 28,800, 31,200, and 33,600 bps

Fax Modulations V.21 CH2 FSK at 300 bps

V.27ter DPSK at 4800 and 2400 bps
V.29 QAM at 9600 and 7200 bps
V.17TCM at 14400, 12000, 9600, and 7200 bps

Carrier Frequencies 1600, 1646, 1680, 1800, 1829, 1867, 1920,
ITU-T V.34 1959, 2000 Hz
Carrier Frequencies: 1800 Hz
AT&T V.32 terbo/
ITU-T V.32bis/V.32
Carrier Frequencies: Transmit originate: 1200 Hz
V.22bis/V.22 or Transmit answer: 2400 Hz
Bell 212A Standard Receive originate: 2400 Hz
(2400 & 1200 bps) Receive answer: 1200 Hz

12

Carrier Frequencies: Transmit originate: 1270 Hz mark
Bell 103/113 1070 Hz space
(300 bps) Receive originate: 2225 Hz mark

2025 Hz space

Transmit answer: 2225 Hz mark

2025 Hz space

Receive answer: 1270 Hz mark

1070 Hz space

Carrier Frequencies: Transmit originate: 980 Hz mark
V.21 1180 Hz space

Receive originate: 1650 Hz mark

1850 Hz space

Transmit answer: 1650 Hz mark

1850 Hz space

Receive answer: 980 Hz mark

1180 Hz space

Carrier Frequencies: Transmit originate: 390 Hz mark
V.23 450 Hz space

Receive originate: 1300 Hz mark

2100 Hz space

Transmit answer: 1300 Hz mark

2100 Hz space

Receive answer: 390Hz mark

450Hz space

Fax Modulations V.21Ch2 FSK at 300 bps

V.27ter DPSK at 4800 and 2400 bps
V.29 QAM at 9600 and 7200 bps
V.17 TCM at 14400, 12000, 9600, and 7200 bps

Fax Carrier V.21 CH2 (half duplex)
Frequencies 1650 Hz mark, 1850 Hz space for transmit originate

1650 Hz mark, 1850 Hz space for transmit answer
V.27ter: 1800 Hz Originate/Answer
V.29 QAM: 1700 Hz Originate/Answer
V.17 TCM: 1800 Hz Originate/Answer

Chapter 1 - Introduction

Transmit Level -13 dBm
Frequency Stability +0.01%
Receiver Sensitivity -43 dBm under worst case conditions
AGC Dynamic 43 dB
Range
Serial Interface EIA RS-232C
Diagnostics Power-on self-test; ITU-T V.54 local analog loop, local digital loop, remote digital

loop.

13

Chapter 1 - Introduction

Firmware Upgrades Via flash PROM technology on Multi-Tech’s BBS
Indicators LEDs for Transmit Data, Receive Data, Carrier Detect, Speed, and Off Hook/Out-

Of-Service

Controls Toggle switches for busy-out
Environmental Temperature range: 0°–50°

Humidity range: 20–90% (noncondensing)

Power 5 VDC at 0.95 A
Requirements ±16 VDC at 0.1 A
Power Consumption Approximately 6 watts
Dimensions, .9 × 11 × 15 in. (2.2 × 28 × 37 cm) H × W × D
card modem
Weight 2.5 lb. (1.1Kg)
Limited Warranty Two years
Fuses F1 (+5V), F2 (-16V), F3 (+16V)

C (32°–120° F)

1.7 Power Supply

DC voltages are supplied to all modems in the CC4800A rack through one or two PS4800A power supplies,
designed for conventional 115 or 230 VAC connection. The power supply is a universal input switching
power supply.

14

Chapter 1 - Introduction

1.8 Modem LED Indicators

The MT2834MR6 has five LED indicators per modem:

TD Transmit Data. This LED blinks when data is being transmitted, on for a space, off for a mark. The

state of this LED matches that of the TD circuit on Pin 2 of the RS-232C interface.

RD Receive Data. This LED blinks when data is received, on for a space, off for a mark. The state of

this LED matches that of the RD circuit on Pin 3 of the RS-232C interface.

CD Carrier On. This LED lights when a valid carrier tone has been detected.

Speed Speed. This LED blinks at different rates to indicate the speed of the data connection:

Data Rate (bps) LED State

12000 or less Off
14400 or 16800 Slow blink rate
19200 or 21600 Medium blink rate
24000 or 26400 Fast blink rate
28800 or more On

OH/OOS Off Hook/Out of Service. This LED lights when the modem is off hook, which occurs when the

modem is dialing, online, or answering a call. The LED flashes when the modem is in the busy­out or out-of-service state.

Note: The PS4800 modem rack power supply has one LED that indicates the presence of all supply voltages.

1.9 Busy Switch

The MT2834MR6 has six two-position Busy switches on the front panel. Each switch can be used to create a
“busy-out” (OOS) condition for one of the six on-board modems (i.e., modem A, B, C, D, E, or F).

To place a modem in the Busy condition, move the appropriate Busy switch to the right. The selected modem
goes off-hook, its OH/OOS LED begins to flash, and incoming calls to this modem get a busy signal. If you
suspect a problem with a particular modem, you can use the Busy switch to have an optional device (such as
a “hunt group”) that looks for a non-busy line to perform a rollover to the next available modem while you
check the status of the Busy modem.

Note: The MultiModemManager can perform the same function using software.

15

1.10 MT2834MR6 Installation Notes

All installation must be done by a qualified service person.

Chapter 1 - Introduction

The installation instructions in your MultiModemManager
of blanking plates to cover empty slots in the card frame. Be sure to follow those instructions.

Warning: Interconnection directly, or by way of other apparatus, of ports marked “SAFETY WARNING see
instructions for use” with ports marked or not so marked may produce hazardous conditions on the network.
Advice should be obtained from a competent engineer before such a connection is made.

This product is intended to be hard wired to the network. The final connection to the network is the
responsibility of the public telecommunications network operator or a person authorized by that operator.

Any other apparatus, including cable and wiring, connected between the MT2834MR6K modem and the
point of connection to any speechband circuit shall comply with the following:

1. The overall characteristics of this apparatus shall be such as to introduce no material effect upon the
electrical conditions presented to one another by the modem and he speechband circuit.

2. The apparatus shall comprise only

a. apparatus approved for the purpose of connection between the modem and a speechband

circuit; and

b. cable and wiring complying with a code of practice for the installation of equipment covered by

this part of BS 6328 or such other requirements as may be applicable.

Note: Such apparatus may have been approved subject to limitations in its use.

Owner’s Manual

include information about the use

1.11 Safety Warnings

• Never install telephone wiring during a lightning storm.

• Never install telephone jacks in wet locations unless the jacks are specifically designed for wet locations.

• Never touch uninsulated telephone wires or terminals unless the telephone line has been disconnected at

the network interface.

• Use caution when installing or modifying telephone lines.

• Avoid using a telephone (other than a cordless type) during an electrical storm. There may be a remote

risk of electrical shock from lightning.

• Do not use the telephone to report a gas leak in the vicinity of the leak

• Ports that are connected to other apparatus are defined as SELV. To ensure conformity to EN 41003,

ensure that these ports are only connected to the same type on the other apparatus.

16

Chapter 2 - Dialing and Answering

Chapter 2 - Dialing and Answering

2.1 Introduction

This chapter describes the dialing and answering capabilities of the MT2834MR6 modems, which are
standard ITU-T V.34 full duplex dial-up modems.

2.2 Dial-Up Automatic Answering

The MT2834MR6 can answer calls automatically. The MT2834MR6 is in originate mode in its idle state.
When it detects an incoming call, it automatically switches to answer mode. You can program the modem to
answer a call after a certain number of rings by using register

S0

(see Chapter 4).

2.3 Dial-Up Handshaking Details

This section briefly explains what happens between two modems in a normal call. We are assuming that
there are MT2834MR6s at both the originating and at the answering end of the telephone line. (If other
brands of modems are used with our modems, they will still communicate, but each manufacturer tends to
use slightly different delay timings and sequences, and many of the brands vary in their indicator
designations.)

Before V.34 negotiation takes place, remote and local modems transfer their functional capabilities using
modulated calling and answering tones. First, the Calling Menu (CM), a data sequence using V.21 low-band
modulation (a handshaking technique originally developed for 300 bps modems), is sent from the originating
V.34 modem to the answering V.34 modem. This describes the range of functional capabilities the originating
modem supports. The answering V.34 modem responds to the CM with a Joint Menu, or JM (using V.21 high­band modulation), indicating the common capabilities of the modem at each end.

Once this is done, a probing signal is passed between the modems to identify impairments in the telephone
channel. After receiving the results of the probing signal, the modem receivers and transmitters will start with
the lowest speed and move up until reaching the highest speed at which they can exchange data. All this
occurs in about five seconds.

Note: In order for the called modem to be able to answer the call, it must have a high DTR (Data Terminal
Ready) signal on pin 20 of the RS-232C interface. This signal comes from the computer or terminal to which
the modem is connected.

Note: If you are using reliable or auto-reliable mode, some additional handshaking takes place. This is
explained in Chapter 5, in the “Auto-Reliable Mode” section.

18

Chapter 2 - Dialing and Answering

2.4 Call Termination

There are several methods by which you can terminate a call, or simply stated, hang up:

1. Command Mode Control. It is possible to enter command mode while remaining online by entering an
escape sequence (
by typing
(bring it on-hook). So the command to hang up a call is three plus signs followed by

2. DTR Control. If DTR (Data Terminal Ready) is turned off for 50 milliseconds or more, a disconnect will
occur. This is probably the most common method used by computer systems at the autoanswer end of
the line to cause the calling modem to disconnect after logoff procedures.

3. Loss of Carrier. Once a data connection has been established, the modem will disconnect if a loss of
carrier occurs for 700 milliseconds (0.7 seconds) or longer. This time can be configured with register
for any time from 0 to 25.5 seconds (in 100 mSec increments). Note that one cause of carrier loss would
be if one of the modems were to disconnect normally.
has no effect at connections above 2400 bps.

4. Abort Timer. Answer Mode: When OH (Off Hook) comes on, the called modem starts a 45 second timer
and waits for a carrier signal from the originating modem. If a carrier is not detected within this period, the
modem disconnects (hangs up) and is ready for another call. Originate Mode: The abort timer functions
the same as in the answer mode, except that the timer begins after the modem has completed dialing,
instead of when it first goes off hook. It is possible to change this 45-second wait period to any other
value from 1 second up to 254 seconds by reconfiguring register

5. Inactivity Timer. Causes the modem to disconnect if no data is being transmitted or received for a
certain period of time. The timer is reset anytime a character passes through the serial port in either a
send or receive direction. This function is controlled by register
by setting
by register

ATO

S30

S30

+++AT<CR>

, or you can terminate the call by using the H command. Typing

to 0, which is the factory default setting, or set to time out after number of minutes selected

.

in most cases). From command mode, you can return to the online state

ATH

will hang up the line

ATH

.

S10

S10

works for speeds of 2400 bps or below.

S7

(see Chapter 4).

S30

. The inactivity timer can be disabled

S10

19

Chapter 3 - AT Commands

Chapter 3 - AT Commands

3.1 Working with AT Commands

The MT2834MR6’s modems are controlled by instructions called AT commands, so called because the
attention characters AT precede each command or command string (sequence of commands). You can send
commands to the modem from your keyboard while in terminal mode, or you can use communications
software to issue these commands automatically.

The MT2834MR6 is in command mode when it is not dialing or online. When it is in command mode, you
have access to a complete communications system that allows you to use several features, including the
basic AT command set described in this chapter. Using the basic AT command set, you can enter phone
numbers for automatic dialing, configure modem options, and monitor telephone activity. In addition, you can
command your modem to perform advanced features such as error correction, data compression, speed
conversion, and more.

This chapter explains command mode, and shows you how to use each of the MT2834MR6’s AT commands.
MT2834MR6 commands and responses are compatible with all systems and with all data communications
software using the AT command set.

For easy reference, the MT2834MR6 has a help command that provides you with short, on-screen
descriptions of the modem commands. The help command is explained later in this chapter.

3.1.1 Modes of Operation

The MT2834MR6 operates in two basic functional modes: command mode and online mode. (There is also
an in-between state, wait-for-carrier, in which the modem is out of command mode but not yet online.) When
you power up the modem, it is in command mode, and is ready to accept and respond to commands from
your keyboard or software.

An MT2834MR6 modem enters online mode after it dials, connects with another modem, and detects a valid
carrier signal. If it does not detect a carrier signal within the time frame controlled by register S7, the modem
abandons the call and re-enters command mode.

You can make the modem enter online mode without dialing by typing either the D command or the A
command.

The modem exits online mode if the carrier signal is lost or intentionally dropped. When this happens, the
modem hangs up and re-enters command mode.

By sending certain “escape” characters to the modem while online, you can make it enter command mode
without losing the carrier signal.

For autoanswer-only applications, you can disable a modem’s ability to recognize AT commands by using
the %DC1 command. When you do this, the MT2834MR6 ignores all commands, and functions as a non­intelligent modem. The %DC1 command and other MT2834MR6 commands are explained later in this
chapter.

21

Chapter 3 - AT Commands

3.2.2 Command Structure

You can control a wide variety of modem operations and options when the modem is in command mode. AT
commands tell the modem to dial a number, to answer a call, to operate at a certain speed, to use a certain
compression technique, and many other functions. AT commands consist of one or two letters, which may be
preceded by an ampersand (&), a dollar character ($), a pound character (#), a percent character (%), or a
greater-than character (>). The Q command, for example, determines whether the modem returns result
codes, while the &Q command selects which AT command set the modem uses.

A parameter after a command (0, 1, 2, etc.) tells the modem which option to use. If you do not specify a
parameter, the modem assumes the 0 (zero) option. E, for example, is the same as E0. You can issue several
commands on a single line (a command string) as long as the line does not exceed 60 characters. Note that
though Q1 is one command, it counts as two characters in the command line.

Each command has a valid range of parameters; for instance, &W can have only 0 or 1 as a parameter. Valid
commands generate an OK result code. A few generate an additional response, such as a list of parameters.
An invalid command, such as &W3, which has a parameter outside the valid range, generates an ERROR
result code. Most commands have a default parameter, one that is enabled when the modem is turned on or
reset with the ATZ or AT&F command. Factory defaults are stored in read-only memory (ROM), and cannot
be changed. User-defined defaults can be stored in nonvolatile random-access memory (NVRAM), and can
be changed or deleted at will.

3.3.3 Command Editing

Always begin a command with the letters AT. You may type the command in upper case or lower case, but
not both. The AT command is not executed until you press the ENTER key. Use the BACKSPACE key to
erase the previous command character; it will not erase the AT characters once they are typed. If your
keyboard has no BACKSPACE key, use CTRL+H. You can change the character recognized by the modem
as BACKSPACE to any other ASCII character by changing register S5.

To cancel an entire command that has been typed but not yet executed, press CTRL+X. This also clears the
command buffer. The effect is the same as backspacing the command, only quicker.

The MT2834MR6 stores characters entered in a command in the modem’s command buffer until they are
executed by pressing ENTER. The command buffer’s capacity is 60 characters. The attention characters (AT)
do not count in the 60 allowed command characters. You may use spaces for increased readability when
typing a command; they are neither stored in the command buffer nor counted in the 60 allowed characters.
Hyphens, parentheses, etc., are not allowed.

If you exceed the 60-character limit or type invalid characters, the command buffer is automatically erased
and an ERROR message is displayed. You must then retype the command within the 60-character limit,
using only the allowed characters.

The commands in this chapter are organized by function. A brief summary follows.

22

Table 3-1. AT Commands by Function
Topic: Command: Description:
Dialing Action D Dial

A: Continuous redial
H On-hook/off-hook

Dial Modifiers P Pulse dialing

T Tone dialing
W Wait for new dial tone
R Reverse originate/answer mode
, Dialing pause
: Continuous redial
; Return to command mode after dialing
! Flash on-hook
@ Quiet answer
$ Call card tone detect

Phone Number D...N Store a phone number
Memory N Dial a stored number

N...N Number linking
L List stored telephone numbers

Chapter 3 - AT Commands

Configuration &W Store configuration
Storage & Recall &F Load default configuration

Z Reset modem

Modem Responses E Echo command mode characters
(Result Codes) Q Result codes: enable/disable

&Q Result codes: Multi-Tech or standard
V Result codes: verbose/terse
X Result codes and call progress
&A Answerback

Online Connection #A Auto speed detection

B Answer tone
%DC Command mode control
&CD Cleardown at disconnect
>DT DTMF detection
#F Fallback modes when online
&G Guard tones
*H Busy-Out After Disconnect
&P Pulse dial ratios
&RD Square wave ring detect
$T Calling tones
#T Trellis-coded modulation
Y Long space disconnect

23

Chapter 3 - AT Commands

Table 3-1. AT Commands by Function (con't)
Topic: Command: Description:
V.34 Controls %F Echo canceler frequency offset comp.

&RA Asymmetric bit rate
#V V.32terbo handshake

RS-232 Interface &C Carrier Detect control
Controls &D Data Terminal Ready control

&R Clear to Send control
&S Data Set Ready control
&RF CTS/RTS interaction control
&SF DSR/CD interaction control

Error Correction & &E0 Non-error correction mode
Data Compression &E1 Autoreliable mode

&E2 Reliable mode
&E14 Data compression disabled
&E15 Data compression enabled
#L V.42 error correction modes
$E V.42 error correction at 300 bps
$A Autoreliable buffering
$F Autoreliable fallback character enable
$R Retransmit count

Speed Controls $BA Baud adjust

$MB Modem baud rate
$SB Serial port baud rate

Immediate Action A/ Repeat last command

I Inquire product code
L5 List current operating parameters
L6 List S-register values
L7 List current operating parameters
L8 List online diagnostics
&RN Rate renegotiation
&RR Retrain

Flow Control &BS Maximum reliable block size

$EB Asynchronous word length (10/11-bit)
&E3 Flow control disabled
&E4 Hardware flow control
&E5 XON/XOFF flow control
&E6 XON/XOFF no pass-through
&E7 XON/XOFF pass-through
&E8 Hewlett Packard ENQ/ACK pacing off
&E9 Hewlett Packard ENQ/ACK pacing on

24

Chapter 3 - AT Commands

Table 3-1. AT Commands by Function (con't)
Topic: Command: Description:

&E10 Non-error correction mode flow control off
&E11 Non-error correction mode flow control on
&E12 Pacing off
&E13 Pacing on
#X Number of XOFF characters sent

Escape +++AT<CR> Default in-band escape sequence
Sequences <BREAK>AT<CR> Alternate out-of-band escape sequence

%E Escape sequence selection
A Force answer mode
O Go back online

Remote %%%AT<CR> Remote configuration escape sequence
Configuration #I Change login password

#S Change setup password

Line Probes %DP Read line probe data

%DF Format line probe data
&RP Immediate line probe
L9 Display signal strength
L10 Display signal to noise ratio
L11 Display noise strength

Diagnostics &T Respond to remote digital loopback signal

U Loopback test modes

25

3.2 Dialing Commands

Dialing commands are used to dial and to hang up.

Ds Dial

s = phone number
Default: none

The letter D in a command causes the modem to dial the telephone number immediately
following it. For example, if you type ATD5551212<CR>, the modem dials the number 555-

1212.
The MT2834MR6 supports several dialing methods. With the D command, you can specify
either pulse (ATDP) or tone (ATDT) dialing. You can also modify the dialing command with
several characters that are explained in “Dial Modifier Commands” in this chapter.
The MT2834MR6 lets you select either smart (wait-for-dial-tone) dialing or blind dialing.
With smart dialing, the modem waits for and detects dial tones and busy signals. With blind
dialing, the modem works with timed pauses (determined by the value of register S6), not
dial tone and busy signal detection. See the X command for more information on blind and
smart dialing.

A: Continuous Redial

If you select smart dialing through the X3 or X4 command, the A: command lets you
continuously redial a busy number until your call is answered. (North American units have a
maximum of 10 redials; this command is not available on U.K. or International models.)
Use this command only if you have reached a busy number after executing a normal dial
command. Type A: (you need not type AT, nor do you need to press ENTER), and the
modem redials the number. If you again reach a busy signal, the modem continues to redial
until it gets through. You can stop the modem from redialing by pressing any key.
To save a step when redialing a phone number, enter a colon (:) at the end of the phone
number. The result is the same as if you had entered A:

Chapter 3 - AT Commands

Note: This command has been largely superseded by software-based continuous redial features.

Hn On-Hook/Off-Hook

n = 0 or 1
Default: none

You can make the modem go on-hook (hang up) or go off-hook with the H command.
H0 (or H) hangs up the modem
H1 brings the line off-hook, just as if you had picked up the telephone handset.

It is not necessary to use the H1 command to bring the line off-hook when using the D
command. The modem automatically goes off-hook when you press ENTER at the end of
the dial command.

26

Chapter 3 - AT Commands

3.3 Dial Modifier Commands

The dial string can include the digits 0 through 9, the pound sign (#), the asterisk (* ), and the letters A, B, C,
or D. The latter are used by some PBXs; the exact function will depend on the PBX manufacturer’s feature set
and implementation. There are also several command characters, called “dial modifiers,” that can be
included within a dialing command after the letter D. Their functions include pulse or tone dialing, pauses in
the dial sequence, automatic redials if a number is busy, and reverting to command mode or switching to
answer mode after dialing.

P, T Pulse or Tone Dialing

Default: P

The MT2834MR6’s modems can dial numbers by using pulse dialing, tone dialing, or a
combination of both methods. Pulse dialing, used by rotary-dial telephones, uses the timed
opening and closing of a relay to encode the numbers. Tone dialing, used by push-button
(touch-tone) telephones, uses dual tone multifrequency (DTMF) dialing.

P selects pulse dialing.
T selects tone dialing.

Insert P or T in the dialing command just before the digits you want to pulse- or tone-dial.
For example, to pulse-dial the number 555-1212, type ATDP5551212 and press ENTER.
To tone-dial the same number, type ATDT5551212 and press ENTER. If neither pulse nor
tone dialing is specified in the dial command, the modem uses whatever method was used
last.
Immediately after the modem has been turned on or reset, it uses pulse dialing, even if you
do not include P in your dial command.
As an example of combining pulse and tone dialing, assume you are calling out of a PBX
(switchboard) system where a 9 has to be pulse-dialed, then the rest of the number has to
be tone-dialed after pausing for a second dial tone. To dial this example, type

ATDP9,T5551212 and press ENTER. (The comma causes a pause.)

W Wait for New Dial Tone

Inserting W into the dialing command causes the modem to wait for another dial tone before
it resumes dialing. (It is not necessary to enter W at the beginning of the dialing command.)
Because the modem must be able to detect the dial tone for this command to work, you also
must select wait-for-dial-tone dialing with the X2 or X4 command.

Rn Reverse Originate/Answer Mode

n = 0 or 1
Default: R0

The R command lets you reverse the modem’s mode of operation from originate to answer,
or from answer to originate; for example, if you need the modem to answer the phone but
then go into originate mode.

R (with no number) at the end of the dialing string reverses in originate mode.
R0 disables mode reversing.
R1 enables mode reversing when R is added to the dial string.

27

Chapter 3 - AT Commands

, Dialing Pause

Enter a comma in the dialing string to make the modem pause while dialing. This pause
lasts two seconds (North American models) or four seconds (U.K. and International models)
for each comma entered. You can force longer pauses by entering multiple commas, or you
can change the length of the pause caused by a comma by setting register S8 to any value
from 0 through 255 seconds (North American models), 4 through 7 seconds (U.K. models)
or 4 through 255 seconds (International models).
Each comma in a dialing command counts as one of the 60 allowed characters.

: Continuous Redial

Enter a colon (:) as the last character of a dialing command, to cause the modem to
continuously redial the number, if it detects a busy signal, until the call is answered. North
American models are limited to 10 redials. You must select smart dialing (X3 or X4) for this
to work. (Not available in U.K. or International models.)

Note: This command has largely been superseded by software-based continuous redial features.

; Return to Command Mode After Dialing

Enter a semicolon (;) as the last character of a dialing command to cause the modem to
return to command mode immediately after executing the command instead of waiting for a
carrier signal and going online.
For example, type ATDT5551212; to tone-dial the number and immediately go back into
command mode. The semicolon is useful when modem data transfer is not desired, as in
voice communications, or in applications using touch tones as a data entry method, such as
bank-by-phone.

! Flash On-Hook

Some switchboard systems react to a momentary on-hook condition. Insert an exclamation
mark into the dialing command to cause the modem to “flash” on-hook for half a second,
just as if you had pressed the switch hook on a telephone set for half a second. (With U.K.
models, the exclamation mark causes the modem to flash on-hook for 90 milliseconds.)
For example, to flash on-hook to transfer to extension 5678 after dialing the number 555­1234, type ATDT5551234,,!5678. The commas cause a 4-second pause.

@ Quiet Answer

Use the @ command to access a system that does not provide a dial tone. The @ command
causes the modem to wait before processing the next character in the dialing string. The
wait is for one or more rings back followed by five seconds of silence.
For example, ATDT5551212@6313550 causes the modem to dial the first number (555-

1212), then wait for the time specified in register S7 for at least one ringback and five
seconds of silence. If the modem detects a busy signal, it hangs up and generates a BUSY
result code. If it does not detect five seconds of silence, it hangs up and generates a NO
ANSWER result code. If it does detect five seconds of silence, it dials the second number
(631-3550).

28

$ Call Card Tone Detect

Use the $ command to dial services that require you to enter your call card number after a
tone. A $ character in the dialing string causes the modem to pause and wait for an AT&T
call card “bong” or a 1600 Hz tone (prevalent in the U.K.). When the modem detects the
tone, it processes the rest of the dialing string. If it does not detect a tone within the time set
by register S7 (a 45-second default), the modem aborts with a NO CARRIER message.
Pressing any key also aborts the $ command.
In the following example, the $ command is placed between an access/phone number and
the caller’s credit card number:

ATDT1028806127853500

Chapter 3 - AT Commands

$123456789

29

Chapter 3 - AT Commands

3.4 Phone Number Memory Commands

The modem can store up to two telephone numbers in nonvolatile memory. You can store the numbers with
the DsNd command, dial them with the Nd command, link them so that one will be automatically dialed after
the other with the NdNe command, or list them with the L command.

DsNd Store a Phone Number

s = phone number
d = 0 or 1
Default: none

You can store a telephone number command string of up to 60 characters in the modem’s
phone number memory. You can store two of these 60-character strings using the DsNd
command. The memory locations are labeled N0 and N1.
Store a command line by typing it as you would any other command, appending the
appropriate Nd memory location.
For example, the tone-dialed number 1-612-555-1212 is stored at memory location N0 by
typing ATDT16125551212N0 and pressing ENTER. The number is not dialed with this
store command.
After storing a number, check to see that it has been stored correctly by typing ATL and
pressing ENTER.
When you store a phone number, you store the entire command string, so you can
effectively create a macro for each number. For example, if you know a particular number
needs to have extended result codes, detect busy or dial tone, error correction, XON/XOFF
flow control, pacing, and data compression enabled, the command to store the entire
command string at location N0 is ATX4&E1&E5&E13&E15DT16125551212N0.

Nd Dial a Stored Number

d = 0 or 1
Default: none

You can automatically dial a telephone number that is stored in the modem’s number
memory by typing ATNn, where n = 0 or 1. For example, you can dial a number stored at N0
by typing ATN0 in terminal mode and pressing ENTER.

Warning: Do not include the letter D in this command, or the stored number will be erased.

NdNe Number Linking

d = 0 or 1
e = 1 or 0
Default: none

Number linking allows the modem to dial a second stored number if the first stored number
is busy. (See the DsNd command.) This command is useful when a computer can be
accessed through more than one phone number. However, it cannot be used with blind
dialing, since busy signals would not be detected.
To link the number in memory location N0 to the number in N1, type ATN0N1 and press
ENTER. You can cycle back and forth between two numbers by linking them several times
in one command: ATN0N1N0N1N0N1<CR>. The only limit on the number of times the
modem can cycle between two numbers is the 60-character maximum allowed in a
command line.

30

L List Stored Telephone Numbers

Use the L command to display dialing commands stored in the modem’s nonvolatile
memory. Typing ATL<CR> displays the stored N numbers in the following format:

0 T14082345678
1 P9,T14089876543

All digits and command letters are displayed. The N number is shown first, followed by the
complete dialing command and telephone number as originally entered.

Chapter 3 - AT Commands

31

Chapter 3 - AT Commands

3.5 Configuration Storage and Recall Commands

The MT2834MR6 stores parameters in two places. It stores factory default parameters in read-only memory
(ROM), and customized parameters in nonvolatile random access memory (NVRAM). You cannot change the
default parameters in ROM; however, you can change parameters in temporary memory and then store them
in NVRAM as custom settings. You can then recall the custom settings as if they were factory default settings.

&Wn Store Configuration

n = 0 or 1
Default: &W1

The &W command stores current AT commands and S-register values in nonvolatile
memory, so you won’t lose your custom settings when you turn off the modem or reset it.
&W0 (or &W) stores all current AT command and S-register values in nonvolatile random
access memory (NVRAM) and configures the modem so that it reads your custom settings
in NVRAM when the modem is turned on or when it is reset with the Z command. (The &F
reset command will continue to read the factory default settings in ROM unless you store
the &F9 command.)
&W1 erases your custom settings in NVRAM when the modem is turned off or reset,
causing the modem to read the factory default settings in ROM when it is subsequently
turned on or reset.
For further information on how the &W command interacts with the reset commands, see
Table 3-2.

&Fn Load Default Configuration

n = 0, 8, or 9
Default: &F8

The MT2834MR6 modems store factory default AT command settings and S-register values
in read-only memory (ROM); they store your custom AT command and S-register values in
nonvolatile random access memory (NVRAM).
The &F0 (or &F) command resets the modem to the factory default values stored in ROM or
to your custom values stored in NVRAM, depending on whether you last stored an &F8 or
an &F9 command.
When &F8 is stored and an &F command is issued, the modem reads the factory default
settings stored in ROM.
When &F9 is stored and an &F command is issued, the &W setting determines whether the
modem reads settings stored in NVRAM or ROM. If the modem is set to &W0, it reads your
custom settings stored in NVRAM. If the modem is set to &W1, it erases your stored settings
(including the &F9 command) and reads the factory default settings stored in ROM. Many
communications programs issue the &F command automatically—the &F9 command allows
you to select your own defaults.
Note that for either an &F8 or an &F9 command to be effective after a reset it must be stored
using the &W0 command.
Table 3-2 summarizes how the &F and Z reset commands interact with the &W command;
note that the &F reset command operates differently from the Z reset command:

32

Table 3-2. Where the Modem Reads Configuration Parameters

Previous Command AT&F and ATZ
AT&W1 (default) ROM ROM

AT&W0 ROM NVRAM
AT&F8&W0 ROM NVRAM
AT&F9&W0 NVRAM NVRAM

Z Reset Modem

The Z command resets the modem to its default configuration and clears the command
buffer. The result is the same as turning the modem off and on. When you type ATZ, the
state of the &W command determines where the default values originate. &W0 defaults
come from the customized configuration in NVRAM, and &W1 defaults come from the
factory default configuration in ROM. Because Z clears the command buffer, it must be the
last command in a command string; normally it is issued by itself: ATZ.
Note that the Z reset command operates differently from the &F reset command. See Table
3-2.

Chapter 3 - AT Commands

Power-On

33

Chapter 3 - AT Commands

3.6 Modem Response (Result Code) Commands

The MT2834MR6’s modems can give responses to commands. The most common one is OK, but the
modems also can alert you or your software to dial tones, busy signals, connection speeds, and whether the
connection is made with error correction or compression enabled. These responses are called result codes,
and they can be terse or verbose, Multi-Tech or standard, basic or extended.

En Echo Command Mode Characters

n = 0 or 1
Default: E1

Normally, when you type commands on the keyboard, the modem echoes the characters
back to the computer or terminal, which displays them on the monitor. Use the E command
to turn this feature off and on.

E0 disables the echo.
E1 enables the echo.

Qn Result Codes Enable/Disable

n = 0, 1, or 2
Default: Q0

You can use the Q command to enable or disable result codes for applications such as
computer-controlled autodialing. You can also use it to disable responses and echo in
answer mode while leaving originate mode still intelligent; this is called the no response
answer mode of operation.

Q0 (or Q) enables result codes.
Q1 disables result codes for applications such as computer-controlled auto-dialing.
Q2 enables the no response answer mode, which leaves originate mode intelligent

while turning off answer mode responses and echo.

&Qn Result Codes (Multi-Tech or Standard AT)

n = 0 or 1
Default: &Q0

The MT2834MR6 gives you a choice between Multi-Tech result codes and standard AT
command set responses. Multi-Tech result codes give you more information, but some
datacomm programs may not be able to use them, in which case, select the standard result
codes.
&Q0 selects Multi-Tech responses with RELIABLE, LAPM, and COMPRESSED modifiers.
With &Q0, the verbose result code for 14,400 bps is CONNECT 14400 LAPM
COMPRESSED.

&Q1 selects AT responses with no RELIABLE, LAPM, or COMPRESSED modifiers. With
&Q1, the verbose result code for 14,400 bps is CONNECT 14400.

34

Vn Result Codes (Verbose/Terse)

n = 0 or 1
Default: V1

The V command controls whether the modem’s result codes display as verbal (“verbose”) or
digital (“terse”) messages. For example, if no carrier signal is detected after dialing, the
result can be displayed either as NO CARRIER, or as the digit 3.

V0 (or V) displays the modem’s result codes as digits.
V1 displays result codes as words.

Xn Result Codes and Call Progress Selection

n = 0–4
Default: X0

The X command selects which result codes the modem provides in command mode and
whether the modem uses “smart dialing” or “blind dialing”. When it smart dials, the modem
listens for dial tones and busy signals and responds to them. When it blind dials, the
modem ignores the signals and relies on timing instead.
X0 causes the modem to blind dial. Instead of looking for a dial tone, it pauses for the time
set in register S6 and then dials regardless. Once a connection has been made, it sends
the Bell 103 basic code CONNECT to the terminal. It ignores any busy signals.
X1 causes the modem to blind dial, but in addition to the basic CONNECT code it provides
extended codes consisting of the word CONNECT and the speed of the connection:
CONNECT 2400, CONNECT 4800, CONNECT 9600, CONNECT 14400, CONNECT 19200,
CONNECT 28800, and so forth. In this mode, the modem does not recognize or respond to
dial tones or busy signals.
X2 causes the modem to wait for a dial tone before dialing. If it does not detect a dial tone
within the time set by S6, the modem sends a NO DIALTONE result code to the terminal. In
this mode, the modem provides extended result codes, but does not respond to busy
signals.
X3 causes the modem to blind dial, but also it looks for a busy signal, and if it detects one, it
sends a BUSY result code to the terminal. In this mode, the modem provides extended
result codes, but it does not respond to dial tones.
X4 causes the modem to look for a dial tone and a busy signal, and respond with NO
DIALTONE or BUSY, as appropriate. It also provides extended result codes. It is the most
useful setting for most datacomm programs.

Chapter 1 - Introduction

&An Answerback

n = 0 or 1
Default: &A0

The &A command controls the MT2834MR6’s answerback feature. Answerbacks are used
in some online realty applications and elsewhere as a security measure. The &A command
enables a modem to return a message to an identification request from another computer.
The default identification is MESSAGE NOT PROGRAMMED.

&A0 disables the answerback feature.
&A1 enables the modem to return a message to an inquiry.

35

3.7 Online Connection Commands

The following commands control the conditions of the online connection.

#An Auto Speed Detection

n = 0–3
Default: #A0

An MT2834MR6 modem can operate as a 33,600 bps, 28,800 bps, 19,200 bps, 14,400 bps,
9600 bps, 4800 bps, 2400 bps, or 300 bps modem. Use the #A command to select the
speed that the modem uses for initial handshaking and subsequent speed selection. The
#A command does not control the originating bps rate of the modem (that is done by the
modem baud rate command $MB), but only the answer mode starting speed.
#A0 causes the modem to start at maximum speed, with fallback to 31,200 to 28,800 to
26,400 to 24,000 to 21,600 to 19,200 to 16,800 to 14,400 to 12,000 to 9600 to 4800 to 2400
to 1200 to 300 bps.

#A1 causes the modem to operate at maximum speed only.
#A2 causes the modem to start at maximum speed, with decremental fallback to 4800 bps.
#A3 causes the modem to start at 2400 bps in V.22bis mode, with fallback to 1200 to 300

bps.

Bn Answer Tone

n = 0 or 1
Default: B0

The B command selects the frequency the modem uses for its answer tone. (The answer
tone is the tone a modem receiving a call transmits to the modem that called it, thus
initiating the handshake between the two modems.) At higher speeds (2400 to 33,600 bps)
there is no conflict, because all protocols use the Bell frequency of 2225 Hz. However, the
ITU-T specification for V.22 has an answer tone frequency of 2100 Hz. This command is
available only in International models.

B0 enables ITU-T frequencies including V.21 (300 bps) and V.23 (1200/75 bps).
B1 enables Bell frequencies including Bell 103 (300 bps).

Chapter 3 - AT Commands

%DCn AT Command Control

n = 0 or 1
Default: %DC0

The %DC command allows you to disable the modem’s ability to respond to AT commands.
It can be used with autoanswer applications in which no call origination is required, with
some UNIX applications, and with other applications that require you to disable the
modem’s command mode.

%DC0 enables command mode.
%DC1 disables command mode.

Note: If you save %DC1 as part of your default configuration, you can re-enable command mode by typing
AT%DC0 and pressing ENTER in the first ten seconds after you power up the modem.

36

&CDn Cleardown at Disconnect

n = 0 or 1
Default: &CD0

In the V.32, V.32bis, and V.34 protocols, a cleardown is sent by one of the modems to
signal the other modem that it is going to hang up. A cleardown is rate renegotiation in
which the modem that is hanging up tells the other modem that it has no speeds that it can
connect at. It is designed to help the remote modem detect a hangup. However, it does take
a second or two to send the cleardown. If you find this delay unacceptable, you can disable
cleardown by using the &CD command.

&CD0 enables cleardown at disconnect.
&CD1 disables cleardown at disconnect.

>DTn DTMF Detection

n = 0 or 1
Default: >DT0

Normally, when it goes off-hook, a fax modem ignores tones from the other end of the
connection unless they are fax or modem handshake tones, in which case it responds in
kind. The >DT1 command causes the modem to report DTMF (touch-tone) tones and fax
calling tones to software for further processing. A typical use would be for a program that
routes calls to specific communications applications depending on the type of call or upon a
DTMF tone added to a dialing string.

>DT0 disables DTMF detection.
>DT1 enables DTMF detection when the modem goes off-hook.

Chapter 3 - AT Commands

#Fn Fallback Modes

n = 0, 1, or 2
Default: #F2

The #F command controls whether the modem will fall back to a lower speed because of an
unacceptable error rate. If line conditions deteriorate, the modem has the ability to fall back
from its original speed to the next lower speed when operating in V.34, V.32terbo, V.32bis,
or V.32 mode. If the error rate becomes too great, the modem performs a retrain at the next
lower speed. If, after the retrain, the error rate is still too high, the modem performs a retrain
at the next lower speed, down to 4800 bps.
If the modem returns online at the original speed after the first retrain, the modem starts a
counter and a timer. If three retrains occur within a two-minute period, the modem falls back
to 4800 bps.
The fallback and fall-forward speeds for the modem are 33.6K, 31.2K, 28.8K, 26.4K, 24.0K,

21.6K, 19.2K, 16.8K, 14.4K, 12K, 9.6K, and 4.8K bps.

#F0 (or #F) disables fallback when online.
#F1 lets the modem fall back from the starting speed to a low speed of 4800 bps in 2400

bps decrements.
#F2 lets the modem fall back when line conditions deteriorate, but also lets it fall forward in
2400 bps increments if line conditions improve.

37

&Gn Guard Tones

n = 0, 1, or 2
Default: &G0 (models outside U.K.)

&G2 (U.K. models only)

The &G command is used to control the presence or absence of guard tones from the
transmitter when in answer mode at either 1200 or 2400 bps. Guard tones are used in
Europe and other areas to allow the modem to function in the telephone systems. Guard
tones are not used in the United States. U.K. models are locked at &G2 (1800 Hz guard
tone).

&G0 disables ITU-T guard tones.
&G1 enables ITU-T 550 Hz guard tone.
&G2 enables ITU-T 1800 Hz guard tone.

*Hn Busy-Out After Disconnect

n = 0 or 1
Default: *H0

The *H1 command causes the MT2834MR6 to remain out of service and return a busy
signal until configuration from the MultiModemManager dedicated management console
has finished. If no configuration option is set on the dedicated management console, the
MT2834MR remains out of service for ten seconds after disconnect. Register S94 controls
the length of the out-of-service, or busy-out, time (see Chapter 4).

*H0 disables busy-out after disconnect.
*H1 enables busy-out after disconnect.

Chapter 3 - AT Commands

&Pn Set Pulse-Dial Ratios

n = 0 or 1
Default: &P0 (Models outside U.K.)

&P1 (U.K. models only)

The &P command sets the time ratios between the open (break) and closed (make) states
of dialing pulses. U.K. models are locked to &P1 (67:33 ratio). See Appendix B for more dial
pulse information.

&P0 sets a pulse dial ratio of 60 ms break to 40 ms make.
&P1 sets a pulse dial ratio of 67 ms break to 33 ms make.

&RDn Square Wave Ring Detect

n = 0 or 1
Default:&RD0 (U.K. and International models)

&RD1 (North American models)

The ringback sound that you hear when you dial a number is generated at the local
telephone office or PBX. Normally, it is a sine wave analog tone. However, some PBXs
generate square wave rings that can go undetected by normal ring detection circuits,
resulting in a failure to make a connection. To enable your modem to detect square wave
rings, use the &RD1 command.

&RD0 enables sine wave ring detection only.
&RD1 enables sine wave and square wave ring detection.

38

$Tn Calling Tone

n = 0 or 1
Default: $T1

The $T command enables or disables the modem’s calling tone, which is required by some
European countries to identify the caller as a modem.

$T0 enables the calling tone.
$T1 disables the calling tone.

#Tn Trellis-Coded Modulation

n = 0 or 1
Default: #T1

The #T command enables or disables trellis-coded modulation (TCM) on the modem. There
is usually no need to disable TCM, except for an unusual line condition called impulse
noise.

#T0 disables TCM.
#T1 enables TCM.

Yn Long Space Disconnect

n = 0 or 1
Default: Y0

When two modems are connected in reliable mode, a link disconnect request packet is sent
to request a disconnect. In non-error correction mode, there is no “polite” way to request a
disconnect. As a result, some “garbage” may be received when a hang-up command is
issued.

Y0 disables the modem’s use of the break signal.
Y1 enables the modem’s use of the break signal, which shuts off the modem’s receiver and

disconnects (both modems must have Y1 enabled).

Chapter 3 - AT Commands

39

3.8 V.34 Commands

The following commands apply only in V.34 mode.

%Fn Echo Canceler Frequency Offset Compensation

n = 0 or 1
Default: %F0

The %F command enables and disables echo canceler frequency offset compensation
which, when enabled, can decrease modem performance.

%F0 disables echo canceler frequency offset compensation.
%F1 enables echo canceler frequency offset compensation.

&RAn Asymmetric Bit Rate

n = 0 or 1
Default: &RA0

The &RA command enables or disables asymmetric bit rate operation in V.34 mode. The
asymmetric bit rate feature lets the modem transmit at one rate while receiving at a different
rate.

&RA0 enables asymmetric bit rate operation.
&RA1 disables asymmetric bit rate operation.

#Vn V.32terbo Handshake

n = 0 or 1
Default: #V1

Some V.32/V.32bis modems have problems handshaking when the MT2834MR6 includes
V.32terbo mode (19,200 bps) in its handshake. The bits that are used in the rate sequence
for V.32terbo can cause handshake failure. Use the #V command to include or exclude
V.32terbo mode from the handshake.

#V0 includes V.32terbo mode in the handshake.
#V1 excludes V.32terbo mode from the handshake.

Chapter 3 - AT Commands

40

Chapter 3 - AT Commands

3.9 RS-232 Interface Commands

These commands define how am MT2834MR6 modem will use and respond to standard RS-232 signals.

&Cn Carrier Detect Control

n = 0, 1, 2, or 4
Default: &C1

The &C command lets you control the Carrier Detect (CD) signal on the RS-232/V.24
interface. Normally, CD goes high when the modem detects a carrier on the
communications link, and drops when it loses the carrier. By using &C, however, you can
force the signal to stay high, or to drop momentarily when the remote modem disconnects.
(This option is useful with some CBX phone systems and mainframe front ends, which
require CD to act in this manner). You can also force the modem to reset when the CD
signal drops.

&C0 forces CD high.
&C1 allows CD to act normally—to go high when the modem detects a carrier, and to drop

when it loses the carrier.
&C2 causes CD to drop for one second on disconnect, and then go high again. (If you want

to set the drop time to something other than one second, change register S24).

&C4 resets the modem when CD drops.

&Dn Data Terminal Ready Control

n = 0, 1, 2, or 3
Default:&D2

The Data Terminal Ready (DTR) signal on pin 20 of the RS-232/V.24 interface must be
high, or “on,” in order for the modem to operate. A high DTR signal tells the modem that the
computer it is connected to is ready to communicate through the modem.
The DTR signal can also be used to cause the modem to reset to its default parameters, as
if you had given the modem an ATZ command.

&D0 (or &D) causes the modem to ignore DTR.
&D1 causes the modem to hang up when DTR drops. While DTR is low, the modem

accepts commands, but will not dial or auto-answer until DTR goes high again.

&D2 acts the same as &D1.
&D3 causes the modem to reset when DTR drops . It will also hang up if it is online.

&Rn Clear to Send Control

n = 0, 1, or 2
Default: &R1

The &R command lets you control the state of the Clear to Send (CTS) signal on pin 5 of the
RS-232/V.24 interface. Normally, CTS follows RTS when the modem is online. You have
three choices. You can force the signal high, allow it to act normally, or set it to stay high
until the modem disconnects, go low momentarily, and then go high again. The last option
is useful with CBX phone systems and mainframe front ends that require CTS to act in this
manner.

&R0 lets CTS act normally, that is, to follow RTS.
&R1 forces CTS high. When the modem goes online, CTS still provides flow control.
&R2 lets CTS drop on disconnect for the time set by register S24, then go high again.

41

&Sn Data Set Ready Control

n = 0, 1, or 2
Default: &S1

Use the &S command to control the state of the Data Set Ready (DSR) signal on the RS­232/V.24 interface. Normally, DSR follows CD. You can force the signal high; allow it to act
normally; or set it to stay high until the modem disconnects, go low momentarily, and then
go high again.

&S0 forces DSR high.
&S1 allows DSR to act normally, that is, to follow CD.
&S2 sets up DSR so that it drops for one second on disconnect and then comes up again.
(If you want to set the drop time to something other than one second, change register S24.)

&RFn CTS/RTS Interaction Control

n = 0 or 1
Default: &RF1

In normal operation, Clear to Send (CTS) follows Request to Send (RTS) when the modem
is online. In other words, if RTS goes off, CTS goes off. In some applications, however, it is
necessary for CTS to operate independently of RTS.

&RF0 enables CTS to follow RTS.
&RF1 enables CTS to operate independently of the state of RTS. See the &R command for

control of CTS.

&SFn DSR/CD Interaction Control

n = 0 or 1
Default: &SF0

Normally, the Data Set Ready (DSR) signal follows the Carrier Detect (CD) signal. In other
words, if CD goes high, DSR goes high. In some applications, however, it may be
necessary for DSR to operate independently of CD.

&SF0 enables DSR to follow CD.
&SF1 enables DSR to operate independently of CD. For control of DSR, see the &S

command.

Chapter 3 - AT Commands

42

Chapter 3 - AT Commands

3.10 Error Correction and Data Compression Commands

You can configure a modem to any of three different V.42 modes of operation (each mode can be with or
without compression). They are the non-error correction, autoreliable, and reliable modes. You can also turn
data compression on or off.

&En Error Correction Modes

n = 0, 1, or 2
Default: &E1

Select the modem’s error correction mode using the &E0, &E1, or &E2 command.
&E0 disables the modem’s V.42 error correction capabilities, and the modem functions as a

non-error correction modem.
&E1 enables autoreliable mode. During the handshaking procedures at the start of the
online connection, the modem queries whether the other modem is using V.42 error
correction. If the modem determines that the other modem is using V.42, it switches itself
into reliable (V.42) mode and enables error correction. If it determines that the other modem
is not using V.42, the modem remains in non-error correction mode.
&E2 enables reliable mode, in which the modem uses its V.42 error correction capabilities
for all transmissions. In reliable mode, the modem must be connected to a modem with a
V.42 protocol (MNP or LAP-M).
The V.42 standard includes MNP Class 3 and 4 and LAP-M error correction methods. The
V.42 mode select command (#L) selects which type of error correction the modem uses for
transmissions.

&En Data Compression

n = 14 or 15
Default: &E15

Data compression is normally enabled, providing &E1 (autoreliable mode) or &E2 (reliable
mode) has also been selected. However, you may wish to turn it off in certain
circumstances.

&E14 disables data compression.
&E15 enables data compression.

#Ln V.42 Error Correction Modes

n = 0–3
Default: #L0

The #L command selects the V.42 error correction method (MNP or LAP-M) the modem
uses when originating a call. In answer mode, the modem ignores the #L command and
accepts whichever V.42 mode, MNP or LAP-M, the originating modem offers.
#L0 causes the modem to negotiate the V.42 error correction method with the answering
modem, and to begin negotiation with LAP-M. If both modems have LAP-M capability, the
modems will use LAP-M mode. If one or both modems do not have LAP-M capability and
both have MNP, the modems will use MNP.

#L1 enables MNP error correction and disables LAP-M.
#L2 enables LAP-M error correction and disables MNP.
#L3 enables LAP-M error correction and disables MNP, but skips the V.42 detection phase
used by the other commands. Both modems must be set with #L3.

43

$En V.42 Error Correction at 300 bps

n = 0 or 1
Default: $E0

At 300 bps, error correction is not normally used.

$E0 disables 300 bps/V.42 error correction altogether.
$E1 enables the modem to function at 300 bps in non-error correction (&E0), autoreliable
(&E1), or reliable (&E2) mode.

$An Autoreliable Buffering

n = 0 or 1
Default: $A0

In autoreliable mode, the modem has four seconds to establish a reliable connection, after
which the modem drops to non-error correction mode. Any data received during this period
will normally be discarded. The $A command causes the modem to buffer (store) data that
is received during the autoreliable time-out period. This data is then output by the modem
after the CONNECT message.

$A0 discards the data received during the autoreliable time-out period.
$A1 buffers data received during the autoreliable time-out period.

$Fn Autoreliable Fallback Character Enable/Disable

n = 0 or 1
Default: $F0

In autoreliable mode, the modem has four seconds to establish a reliable connection. If a
single carriage return is received from the remote modem during this period, the
autoreliable modem assumes that the remote modem is not in reliable mode, and drops to
non-error correction mode. The carriage return is the only character that causes the modem
to drop to non-error correction mode. Any other data is either buffered or discarded.
Use the $F command to enable this feature.
You can use the autoreliable fallback character ($F) and autoreliable buffering ($A)
commands together to cause the modem to buffer all data received up until the carriage
return, and then drop to non-error correction mode. All data received is then output
following the CONNECT message.
$F0 causes the modem not to fall back to non-error correction connect if a carriage return is
received.
$F1 causes the modem to fall back to non-error correction connect if a carriage return is
received.

Chapter 3 - AT Commands

$Rn Retransmit Count

n = 0 or 1
Default: $R0

If errors are received during a reliable connection, the modem re-sends the block of data
that contained an error. If another error occurs, it re-sends the block again. The modem
counts the number of times that a data block is re-sent.
$R0 causes the modem to disconnect if the same block of data is re-sent 12 times without
being received properly, on the assumption that the line is unsuitable for transmission.
$R1 causes the modem to disable the retransmit counter, so that the modem keeps trying to
send data and will not abort, no matter how many times the same block is resent. Type

AT$R0 to disconnect the modem if all attempts to re-send the block fail.

44

Chapter 3 - AT Commands

3.11 Speed Conversion Commands

Speed conversion allows the MT2834MR6 to communicate at a fixed speed through the serial port while
communicating at an independent speed over the online communications link. Speed conversion is
necessary for data compression, since data compression requires data to be sent from the computer to the
modem at a rate up to four times faster than the modem’s transmission speed.

Speed conversion is also useful for an autoanswer modem connected to a computer that does not have
autobaud capability, since the computer must be set at a fixed baud rate regardless of the speed at which the
modem communicates over the phone line.

$BAn Baud Adjust

n = 0 or 1
Default: $BA0

Turning baud adjust off turns speed conversion on; turning baud adjust on turns speed
conversion off.
When baud adjust is on, the modem matches its RS-232 serial port speed to any changes
in the computer’s serial port speed in originate mode, or to the speed of the originating
modem when it’s in answer mode. With baud adjust on, the speed at which the modem
communicates over the phone line is always the same as the speed at which it
communicates via its RS-232 serial port.
When speed conversion is on, the modem does not adjust its speed at the serial port to
match its transmission speed. Serial port speed and transmission speed can therefore be
set independently. Speed conversion is necessary for a high speed modem that is
connected to a limited speed serial port.

$BA0 turns baud adjust off and speed conversion on.
$BA1 turns baud adjust on and speed conversion off.

$MBn Modem Baud Rate

n = speed in bits per second
Default: $MB33600

The $MB command sets a modem’s initial transmission speed for originate mode. In V.32
mode (9600 bps), it also sets the transmission speed for answer mode. With speed
conversion on, this transmission speed can be different from the serial port speed.
When the modem answers a call from another modem, it automatically switches its
transmission speed to match the calling modem. However, if the MT2834MR6 originates a
call to another modem that is unable to connect at the same transmission speed, the
MT2834MR6 automatically drops to a lower speed in an attempt to match the speed of the
other modem.
Speed conversion must be on for this command to work. If baud adjust is on ($BA1), speed
conversion is off and a modem baud rate command will be ignored. The S48 register also
can affect maximum transmission speed. See Chapter 4.

$MB75 ITU-T V.23 mode $MB300 300 bps
$MB1200 1200 bps $MB2400 2400 bps
$MB4800 4800 bps $MB7200 7200 bps
$MB9600 9600 bps $MB12000 12,000 bps
$MB14400 14,400 bps $MB16800 16,800 bps
$MB19200 19,200 bps $MB28800 28,800 bps
$MB33600 33,600 bps (default)

45

$SBn Serial Port Baud Rate

n = speed
Default: $SB57600

The $SB command sets the speed of the MT2834MR6’s serial port in both originate and
answer modes. Speed conversion allows you to set this serial port baud rate at a fixed
speed of up to 115,200 bps, regardless of the modem’s transmission speed setting.
For this command to work, the modem’s baud adjust feature must first be turned off with the
$BA0 command. When baud adjust is on, as soon as the modem receives its first AT
command, it automatically adjusts its serial port baud rate to match the speed of the
computer or terminal to which it is connected. However, in applications such as automatic
answer, the modem may not receive AT commands. In this case it is helpful to be able to
preset the serial port baud rate with the $SB command.
In addition to setting the modem’s serial port speed, this command sets the speed at which
the modem issues command mode responses (result codes).

The MT2834MR6 accepts AT commands at any speed, regardless of the speed preset by
the $SB command. If the modem receives a command at a speed different from the preset
speed, the modem switches its serial port baud rate to match the new command speed,
even though the baud rate value stored by the $SB command remains the same. This
provides you with a convenient way to switch the serial port speed while still making it easy
to automatically return to the original speed the next time the modem is powered up or
reset.

$SB300 300 bps $SB1200 1200 bps
$SB2400 2400 bps $SB4800 4800 bps
$SB9600 9600 bps $SB19200 19,200 bps
$SB38400 38,400 bps $SB57600 57,600 bps
$SB115200 115,200 bps ( default)

Chapter 3 - AT Commands

46

Chapter 3 - AT Commands

3.12 Immediate Action Commands

Use these commands to get information about AT commands and the current settings of the modem. For
additional immediate action commands, see “Line Probe Commands.”

A/ Repeat Last Command

Default: None

Type A/ to repeat the previous command. Do not precede this command with AT or press
ENTER to execute it.

In Inquire Product Code

n = 0, 1, or 2
Default: none

Some systems or software packages automatically check the identification of the modem by
using the I command. Besides using it to check the modem ID, you can use the I command
to check the version number of the modem’s built-in software, known as firmware.

ATI0 or ATI requests the modem’s ID number.
ATI1 requests the modem’s firmware version number. You can use this command to identify

your modem’s firmware level when calling Technical Support.

ATI2 requests the product name, such as MT2834MR6.
ATI5 requests the digital signal processor version number.

L5, L7 List Current Operating Parameters

Default: none

The L5 and L7 commands cause your modem to list its current operating parameters. These
lists are useful when you are changing communications software, or when you are
changing modem default settings. All modem configuration parameters are listed.

ATL5 lists the modem’s current operating parameters.
ATL7 lists additional modem parameters.

L6 List Current S-Register Values

Default: none
ATL6 lists the current values in the modem’s S-registers. This information can be very

useful if you wish to change S-register values.

L8 List Online Diagnostics

Default: none

The L8 command displays the modem’s online status. You can print this display and use it
as a modem status report or as diagnostic information (such as when calling Technical
Support).
To enter this command while online, type +++ATL8<CR>. Your modem’s online status will
be displayed, listing current operating conditions such as link type, line speed, serial speed,
line quality, and reason for last disconnect.
If you type +++ATL8 with the modem online, the current online status will be displayed. If
you type ATL8 with the modem in command mode, the most recent online status will be
displayed. If you type ATL8 immediately after modem power-up, the message NO
INFORMATION AVAILABLE will be displayed.

47

&RN Rate Renegotiation

Default: none

The &RN command forces the modem to perform a rate renegotiation while online. To issue
it, you must first escape to command mode by issuing the +++AT<CR> command.

&RR Retrain

Default: None

The &RR command forces the modem to perform an immediate retrain while online. To
issue it, you must first escape to command mode by issuing the +++AT<CR> command.

Chapter 3 - AT Commands

48

Chapter 3 - AT Commands

3.12 Flow Control Commands

Flow control refers to the techniques used by data terminal equipment and the modem to pause and resume
the flow of information between them. It prevents a device from accepting more data than it can handle. The
modem implements flow control in both directions. When the modem halts the flow of data, it is called flow
control, and when the computer halts the flow, it is called pacing.

&BSn Maximum Reliable Block Size

n = 0 or 1
Default: &BS1

When the modem is in reliable mode, use the &BS command to set the maximum size of a
data block. MNP Class 3 sends a 64-character block, while Classes 4 and 5 normally send
blocks of 256 characters or less. Reducing the block size for MNP 4 and 5 may improve
overall throughput whenphone lines are noisy; however, it also could slow data transfer if
line quality is good.

&BS0 sets the maximum transmit block size to 64 characters.
&BS1 sets the maximum transmit block size to 256 characters.

$EBn Asynchronous Word Length

n = 0 or 1
Default: $EB0

The MT2834MR6 can operate with either a 10-bit format (one start bit, seven data bits, one
parity bit, and one stop bit) or an 11-bit format (one start bit, eight data bits, one parity bit,
and one stop bit) in both command and online modes.
$EB0 enables a 10-bit format It automatically detects parity when an AT command is
issued.

$EB1 enables an 11-bit format.

&E3 Flow Control Disable

The &E3 command completely disables data flow control initiated by the modem.

&E4 Hardware Flow Control

Factory default. The &E4 command enables the modem’s use of the Clear to Send (CTS)
signal on the RS-232/V.24 interface to regulate data flow. When CTS drops, data flow is
suspended until the signal goes high again. This method of flow control works in
conjunction with pacing (i.e., computer-initiated flow control), which uses the Request to
Send (RTS) signal on the RS-232/V.24 interface. Hardware flow control cannot be enabled
unless an active error correction protocol is selected.

49

&E5 XON/XOFF Flow Control

XON/XOFF flow control is an in-band method of data flow regulation used by the modem or
computer (i.e., by flow control or pacing). If you issue the &E5 command to the modem, it
will respond to XON/XOFF pacing, and use XON/XOFF characters as its own method of flow
control to the computer.
In-band data regulation means that the XON and XOFF characters (^Q and ^S, respectively)
are inserted into the stream of data rather than using separate control lines. When an XOFF
character is detected, the data stream is suspended until an XON character is detected. The
drawback to using this method of pacing is that some files may contain these characters. If
such a file is transferred using a modem, the file transfer can be suspended indefinitely.

&En XON/XOFF Pass-Through

n = 6 or 7
Default: &E6

When XON/XOFF pacing is active, the local modem has two options regarding the XON and
XOFF characters. It can respond to and discard the characters from the computer, or it can
respond to the characters and pass them through the datacomm link to the remote modem,
thereby pacing the remote modem as well.

&E6 causes the modem to respond to and discard the XON and XOFF characters.
&E7 causes the modem to respond to the characters and pass them through the data link to

the receiving modem.

&En Hewlett Packard ENQ/ACK Pacing

n = 8 or 9
Default: &E8

If the MT2834MR6 is used with Hewlett Packard (or compatible) equipment, it can be
configured to respond to ENQ/ACK pacing as a complement to any other form of active flow
control or pacing. In that case, pacing from the Hewlett Packard equipment is processed
according to the HP protocol.

&E8 causes the modem to ignore ENQ/ACK pacing.
&E9 causes the modem to respond to the ENQ (^E) and ACK (^F) characters.

Chapter 3 - AT Commands

&En Non-Error Correction Mode Flow Control

n = 10 or 11
Default: &E10

When two modems are connected in non-error correction mode, XON/XOFF flow control
can be used as a complement to XON/ XOFF pacing.

&E10 disables non-error correction mode flow control.
&E11 enables non-error correction mode flow control.

50

&En Pacing (Computer-Initiated Flow Control)

n = 12 or 13
Default: &E13

Pacing is the means by which the DTE (data terminal equipment—your computer or
terminal) regulates the stream of incoming data. It is only enabled when the modem has
some form of flow control active, such as RTS/CTS or XON/XOFF. When pacing is enabled,
the modem responds to the DTE’s pacing signals. When pacing is disabled, the modem
ignores any pacing signals from the DTE.

&E12 disables pacing.
&E13 enables pacing.

#Xn Number of XOFF Characters Sent

n = 0 or 1
Default: #X0

The #X command allows the modem to send either a single or multiple XOFF characters
when the modem’s buffer becomes full. When the buffer is full, the next character received
causes an XOFF character to be sent. In default mode, only one character is sent until the
buffer reaches the XON level; however, it is also possible to send one XOFF character for
every character received after the buffer is full.

#X0 causes only a single XOFF character to be sent after the buffer is full.
#X1 causes one XOFF character to be sent for every character received after the buffer is

full.

Chapter 3 - AT Commands

51

Chapter 3 - AT Commands

3.13 Escape Sequences

Escape sequences (escape codes) cause the modem to enter command mode from online mode without
disconnecting the call. There are two local escape sequences used by the modem, +++AT<CR> and

<BREAK>AT<CR>, and one remote escape sequence, %%%AT<CR> (see “Remote Configuration”).

+++AT<CR> In-Band Escape Sequence

When the modem is online with a remote modem, enter command mode (without
disconnecting the call) by typing this escape code. The default escape code is three plus
signs (+++) followed by the letters AT, up to 10 command characters and ENTER. The
modem escapes to command mode, executes the command (if any), then remains in
command mode.

<BREAK>AT<CR> Out-of-Band Escape Sequence

An alternate escape method uses a break signal as the escape code. The break signal is
ten or more zero bits issued by data communications software. This allows the DTE to
signal the modem without the modem interpreting data characters as modem control
characters. The break signal is followed by the letters AT, up to 60 command characters,
and ENTER. The modem executes the command and immediately returns to online mode,
unless the command is to hang up and/or reset the modem (an H or Z command). In the
latter case, the modem escapes to command mode after executing the H or Z command.

%En Escape Sequence Options

n = 0–5
Defaults: %E1 and %E4

Optional settings cause the modem to respond to the <BREAK> method, or respond to
either the +++ or the <BREAK> methods, or for the modem to ignore both methods and not
escape. The %E command is used to select these options as follows:

%E0 Modem doesn’t escape
%E1 +++ AT<CR> escape method (factory default).
%E2 <BREAK> escape method.
%E3 Either +++ or <BREAK> escape methods.
%E4 Disables OK response to +++ (factory default).
%E5 Enables OK response to +++.
%E1 %E5 Enables +++ method and OK responses to +++.
%E3 %E5 Enables +++ or <BREAK> method and OK responses to +++.

A Force Answer Mode

A

Use the
mode to immediately bring the modem off-hook, out of command mode and into online
answer mode, transmitting the carrier signal over the phone line. If no responding carrier
tone is received within forty-five seconds (or by the time you have specified in register
the modem stops transmitting and hangs up, returning to command mode.

O Go Back Online

Use the O command to bring the modem out of command mode and back into online mode.
The O command reverses the result of entering the escape code. The O command brings
the modem into whichever online mode (originate or answer) that it was in prior to entering
command mode.

command to force the modem into answer mode. Type

ATA

when in command

S7

),

52

Chapter 3 - AT Commands

3.14 Remote Configuration Commands

When you are online with another Multi-Tech modem, you can issue AT commands to it by sending a remote
configuration escape sequence. The remote modem responds by displaying a menu and asking for a setup
password. The MT2834MR6 has two default passwords. Please note that if you change them, you cannot
retrieve them by resetting the modem by using AT&W1; you must know the new passwords to make any
further changes. For further information on remote configuration, see Appendix I, “Remote Configuration.”

%%%AT<CR> Remote Configuration Escape Sequence

Enter the remote configuration escape sequence to initiate remote configuration when you
are online with another Multi-Tech modem. The default escape sequence used by the
MT2834MR6 is three percent signs (%%%) followed by the letters AT and ENTER. The
remote configuration escape character, which is stored in register S13, can be changed
either locally or remotely for greater security.

#Ixxxxxx Change Login Password

xxxxxx = password
Default: #IMULTI-TECH

Use the #I command to enter or change the remote configuration login password.
AT#Ixxxxxx enters the current remote configuration login password, where xxxxxx

represents the password. If the password is wrong, the remote modem responds with
ERROR; if it is correct, the remote modem responds with OK, and you can proceed with the

#S command.
AT#I=xxxxxx stores a new remote configuration login password, where xxxxxx represents

the password. The password is case sensitive, and can be any combination of upper and
lower case keyboard characters. It must be six to ten characters in length.

#Syyyyyy Change Setup Password

yyyyyy = password
Default: #SMODEMSETUP

Use the #S command to enter or change the remote configuration setup password. Before
you can use it, you must enter the login password using the #I command.
AT#Syyyyyy enters the current remote configuration password, where yyyyyy represents
the password. If the password is wrong, the remote modem responds with ERROR; if it is
correct, the remote modem responds with OK, and you can proceed with the next command.
AT#S=yyyyyy stores a new remote configuration setup password, where yyyyyy represents
the password. The password is case sensitive, and can be any combination of upper and
lower case keyboard characters. It must be six to ten characters long.

53

Chapter 3 - AT Commands

3.15 Line Probe Commands

Before V.34 negotiation, the local and remote modems use modulated calling and answering tones to
exchange capability information . If V.34 mode communication is successful, probing signals are exchanged
to identify impairments in the telephone channel. Using the results of these line probes, communication
parameters are set, including carrier frequencies and data rates used for transmission. The following
commands apply to modems only in V.34 mode.

%DP

n Read Line Probe Data

n

= 0 or 1

Default:

The modem does not normally store data acquired during line probe. To examine the line
probe data using the
line probe data.

%DP0
%DP1

%DF

n Format Line Probe Data

n

Default:

Use this command to selects line probe data displayed as a graph with the Y axis showing
signal strength in dBm, or as a table with dBm values shown numerically. The graph format
shows data in 150 Hz increments from 150 Hz to 3750 Hz. The table format shows data in
75 Hz increments from 150 Hz to 3750 Hz.

%DF0
%DF1

%DP0

L9, L10

disables reading of line probe information during the handshake.
enables reading of line probe information during the handshake.

= 0 or 1

, or

L11

commands, set the

%DP1

%DF0

displays line probe data in graph format.
displays line probe data in table format.

command to read and store

&RP

L

n Display Line Probe Data

Immediate Line Probe
Default: none

This command initiates a retrain that makes the processor read line probe information for
display using the
command mode while remaining online. To combine both actions, use the following
command string:
The modem will not read and store the line probe information from this retrain unless a

%DP1

command is first issued.

n

= 9–11

Default: none

These immediate action commands cause the modem to display line probe information
when it is in V.34 mode. The line probe information must first be read and stored by the
modem (see “Read Line Probe Data”). Data format is controlled by the Format Line Probe
Data command,
The display commands are valid only in online mode. To use them online, you must first
escape to command mode with

ATL9

displays signal strength information.

ATL10
ATL11

displays the signal to noise ratio (SNR).
displays noise information.

L9, L10

+++AT&RP<CR>

%DF

, and

L11

commands. Before issuing this command, escape to

.

.

+++AT<CR>

. To return online, enter

ATO

.

54

Chapter 3 - AT Commands

3.16 Diagnostic Commands

The MT2834MR6 has two diagnostic commands and four diagnostic modes. The power-on self-test is
activated every time power is applied. The U command selects a loopback test, while the &T command
enables a modem to respond to a loopback test from another modem. See Chapter 6, “Testing the
MT2834MR6,” for a fuller discussion. Refer to the L8 command to see how to list the diagnostic online status.

&Tn Respond to Remote Digital Loopback Signal

n = 4 or 5
Default: &T5

The MT2834MR6 has several self-test features, discussed in Chapter 6. The &T command
enables or disables the modem’s ability to recognize the remote digital loopback (RDL) test
signal. (See Chapter 6 for remote digital loopback test procedures.)

AT&T4 lets the modem respond to an RDL signal, and places it in digital loopback.
AT&T5 causes the modem to ignore the RDL signal.

Un Loopback Test Modes

n = 0–3
Default: None

Loopback tests send data through the modem in such a way that it loops back to the
terminal where it was entered, testing all the circuits along the way. The U command selects
from several loopback tests. See Chapter 6, “Testing Your Modem,” for more information.

ATU0 places the modem in originate mode for the local analog loopback test.
ATU1 places the modem in answer mode for the local analog loopback test.
ATU2 performs the remote digital loopback test.
ATU3 performs the local digital loopback test.

55

Chapter 4 - S-Registers

4.1 Introduction

Chapter 4 - S-Registers

This chapter describes the MT2834MR6’s
configuration information is stored. Whereas AT commands tell a modem

how

modem
hence the term
command to change it.

to do it. Each S-register has a name that consists of the letter S and a number (S0, S1, S2, etc.),

S-register

. Use the Sr? command to read the value stored in an S-register, and the Sr=n

S-registers

, which are small regions of memory where modem

4.2 S-Registers

S0 Number of Rings Until Modem Answers

Unit: 1 ring
Range: 0–255
Default: 1

S0 defines the number of rings the modem waits before answering an incoming call. The

default value is one ring, which causes the modem to answer the call immediately after the
first ring. The maximum number of rings that can be configured is 255. Setting the value to
zero disables autoanswer.

S1 Ring Count

Unit: 1 ring
Range: 0–255
Default: 0

S1 counts the number of rings that have occurred. It is a “read” type of register and is

seldom, if ever, used in typical operation. Each time an incoming ring signal is detected, S1
increases its value by one, up to a maximum of 255. If you set S1 to a value other than its
default value of zero, or if the value is increasing with rings, this new value remains stored
in S1 for eight seconds after the last ring is counted, after which the value reverts back to
zero.

what

to do, S-registers tell the

S2 Escape Code Character

Unit: Decimal
Range: 0–127
Default: 43 (+)

S2 defines the escape code character by its decimal ASCII code. The default character is

the plus (+) sign (decimal 43). S2 may be set for any ASCII character. Setting an S2 value
greater than 127 results in no escape character, and therefore no means of entering
command mode from online mode without breaking the online connection, unless you use
the BREAK method. See Appendix H, “Multi-Tech Escape Methods.”

Note: If you change the S2 value, you must make corresponding changes in your data communications
software.

57

Chapter 4 - S-Registers

S3 Return Character

Unit: Decimal
Range: 0–127
Default: 13 (^M)

S3 defines the carriage return character by its decimal ASCII code. The default setting is the

^M character (decimal 13), which is the code for the ENTER key on most keyboards. S3
may be set for any ASCII character.

Note: If you change the S3 value, you must make corresponding changes in your data communications
software.

S4 Line Feed Character

Unit: Decimal
Range: 0–127
Default: 10 (^J)

S4 defines the line feed character by its decimal ASCII code. The default setting is ^J

(decimal 10), which is the code for the line feed key on most keyboards that have such a
key. S4 may be set for any ASCII character.

S5 Backspace Character

Unit: Decimal
Range: 0–127
Default: 8 (^H)

S5 defines the backspace character by its decimal ASCII code. The default setting is the ^H

character (decimal 8), which is the code for the BACKSPACE key on most keyboards. S5
may be set for any ASCII character.

Note: If you change the S5 value, you must make corresponding changes in your data communications
software.

S6 Wait Time for Dial Tone

Unit: 1 second
Range: 2–255 (North America)

4–255 (International)
4–7 (U.K.)

Default: 2 (North America)

4 (International and U.K.)

S6 defines the length of time the modem waits after the ENTER key is pressed before

executing a dial command. The default setting is two seconds for North America, four
seconds elsewhere.

58

S7 Time for Carrier (Abort Timer)

Unit: 1 second
Range: 1–255 (U.S.A.)

1–45 (Canada and International)
1–55 (U.K.)

Default: 45 (North America and International)

55 (U.K.)

S7 determines the abort timer delay time, which is the amount of time your modem will wait

for a carrier signal before it disconnects. The default value is 45 seconds, except the U.K.
model, for which it is 55 seconds. This means that, after dialing, the modem waits for a
carrier signal for up to 45 or 55 seconds and, if none is detected, aborts the call. The

S7

maximum
International models, and 55 seconds for the U.K. model.

S8 Pause Time for Comma

Unit: 1 second
Range: 0–255 (North America)

Default: 2 (North America)

S8

determines the length of the pause caused by a comma in a dialing command. The
default setting is two seconds for the North American model, and four seconds for the
International and U.K. models.
length of time the modem waits before retrying a call after it detects a busy signal. Some
computer systems need more than two seconds to reset, in which case you should increase
the value of

value is 255 seconds for the U.S.A. model, 45 seconds for Canadian and

4–255 (International)
4–7 (U.K.)

4 (International and U.K.)

S8

.

S8

may be set for up to 255 seconds.

Chapter 4 - S-Registers

S8

also defines the

S9 Carrier Detect Response Time

Unit: 100 ms
Range: 1–255
Default: 6

S9

determines the time delay between when the modem first detects a valid incoming

carrier signal and when the modem turns on its Carrier Detect circuit. The default setting is
600 milliseconds (six units of 100 ms each).

S10 Carrier Loss Disconnect Delay Time

Unit: 100 ms
Range: 1–254, 255
Default: 7

S10

defines the length of time after a loss of carrier signal before the modem disconnects.
The default setting is 700 ms (seven units of 100 ms each). Maximum delay is 25.4 seconds
(decimal 254). Setting the
of carrier.

S10

value to 255 causes the modem not to disconnect with loss

S9

may be set for up to 25.5 seconds.

59

S11 Tone Dialing Spacing and Duration

Unit: 1 ms
Range: 1–255 (U.S.A.)

80–255 (Canada, U.K., International)

Default: 70 (U.S.A.)

80 (Canada, U.K., International)

S11

sets the speed of tone dialing (spacing and tone duration times). The default value is
70 units for domestic models and 80 units for Canadian and International models, where
each unit is one ms. In other words, for domestic modems, each tone is sustained for 70 ms
followed by a 70 ms pause. The minimum
50 ms (50 units). Very few telephone systems can handle anything faster than that. The
maximum S11 value is 255 ms (255 units).

S13 Remote Configuration Escape Character

Unit: Decimal
Range: 0–127
Default: 37 (%)

S13

defines the remote configuration escape character by its decimal ASCII code. The
default is the percent character (decimal 37). When you enter the
three consecutive times from a remote site, your modem responds with its remote
configuration procedure. A value of 0 disables remote configuration.

S17 Changing Break Time

Unit: 10 ms
Range: 1–255
Default: 25 (250 ms)

S17

defines the break time (space) the modem sends the DTE when it receives a break
signal from a remote modem. Break duration is adjustable in 10 millisecond increments.
The default is set to 25, for a 250 millisecond break.

Chapter 4 - S-Registers

S11

value allowed by most telephone systems is

S13

-defined character

S13

S24 PBX/CBX Disconnect Drop Time for DSR/CTS/CD

Unit: 50 ms
Range: 0–255
Default: 20 (1 second)

Some PBX and CBX phone systems require the modem’s DSR, CTS, and/or CD signals to
drop briefly when calls are disconnected. The MT2834MR6’s
can cause the modem to drop these signals for a specified time upon disconnect, and then
bring the signals up again.
setting of 20 results in a one-second drop time, which is what most PBX/CBX systems with
this requirement need.

S25 DTR Dropout Time

Unit: 100 ms
Range: 0, 1–255
Default: 0 (50 ms)

S25

sets the amount of time that DTR must be dropped before the modem disconnects.
Typically, a disconnect occurs when DTR is dropped for 50 milliseconds or more. This
dropout time can be increased up to a maximum of 25.5 seconds. The S25 unit value for
zero is 50 ms. For values from 1 through 255, the unit value is 100 ms.

S24

defines the length of time that the signals drop. The default

&R, &S

, and &C commands

60

S30 Inactivity Timer

Unit: 1 minute
Range: 0, 1–255 minutes
Default: 0 (disabled)

S30 can be used to cause the modem to disconnect if no data is transmitted or received for

a specified time. S30 runs during both reliable and non-error correction connections. The
timer restarts any time a data character passes through the serial port (either sent or
received). If noise on the phone line causes an error to be received during non-error
correction mode, this also will restart the S30 timer. The factory default of zero disables the
timer.

S32 Time Lapse for Escape Sequence

Unit: 100 ms
Range: 0–255
Default: 20 (2 seconds)

S32 sets the time period to validate the escape sequence. If the S32 time interval expires

before you press ENTER, then the escape sequence is aborted. The default is two seconds.

S34 Command Buffer Length After Online Escape Sequence

Unit: Decimal
Range: 0–60
Default: 10

Sets the number of characters allowed in an AT command after an in-band online escape
(+++ method). If the number of characters after “AT” exceeds the S34 buffer length value,
then the buffer is flushed and the escape sequence is aborted.

Chapter 4 - S-Registers

S36 DTR Busy-Out Time

Unit: 1 second
Range: 0–255
Default: 0 (disabled)

S36 sets the time between when DTR goes inactive and when the modem goes off-hook.

The DTR busy-out feature is disabled when S36 is set to 0.
Normally, when the DTR signal from the computer goes inactive, the modem goes on-hook
after a time that is set by S25. If S36 is set for a non-zero time, the modem then waits for the
time set by S36; if DTR has not gone active again in that time, the modem goes off-hook,
causing a busy signal for callers. The busy-out state ends when DTR goes active again.

S37 DTR Busy-In Time

Unit: 1 second
Range: 0–255
Default: 5

S37 sets the time between when DTR goes active and when the modem goes on-hook, if
S36 has caused it to go off-hook.

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Chapter 4 - S-Registers

S43 Force V.34 Connect Speed

Unit: N/A
Range: 0, 33, 31, 28, 26, 24, 21, 19, 16, 14, 12, 96, or 48
Default: 0 (disabled)

S43

forces the modem to attempt to connect at a fixed speed in V.34 mode. The two-digit
value corresponds to the first two digits of the speed (

21.6K bps,
and allows the modem to establish the best speed for the conditions.

S43=96

sets it to 9600 bps, etc.). The factory default of zero disables this feature

S43=21

Note: The $MB command overrides S43 if the $MB command is set to a speed other than 33,600 bps.

S48 Maximum V.34 Connect Speed

Unit: N/A
Range: 0, 33, 31, 28, 26, 24, 21, 19, 16, 14, 12, 96, or 48
Default: 0 (disabled)

S48

sets the maximum speed in bps at which the modem can attempt to connect in V.34
mode. The two-digit value corresponds to the first two digits of the speed (
maximum connect speed to 26.4K bps,
allows you to set lower speeds for line conditions that will not support higher V.34 speeds
such as 33.6K, 31.2K, 28K, 26.4K, or 24K. The factory default of zero disables this feature
and allows the modem to establish the best speed for the conditions (in effect, it sets a
maximum connection attempt of 33.6K).

S94 Out-of-Service Time

Unit: 1 second
Range: 0–254, 255
Default: 45

S94

sets the maximum number of seconds, from 0 through 254, that the modem remains out
of service when the
out of service indefinitely. However, if the modem receives an enable command from the
management program while the modem is out of service, the modem returns to service
immediately, before the

S48=48

*H1

command is active. A value of 255 causes the modem to remain

S94

time expires.

sets it to 4800 bps, etc.). This register

sets the connect speed to

S48=26

sets the

62

Chapter 4 - S-Registers

4.3 Reading and Assigning S-Register Values

Use the S command to assign a value to an S-register and to read an S-register’s current value.
To read an S-register value, in terminal mode, type S

press ENTER. For example, to display the value of register
will appear as a three-digit decimal number (e.g.,

To assign a new value to an S-register, type S
number. Convert all ASCII characters to their decimal equivalents before entering them. S-register decimal
values are 0–127 for ASCII characters, and 0–255 for numeric values. To make the change permanent, use

&W0

the

command.

,

the S-register number, and a question mark (?), and

S7

, type ATS7? and press ENTER. The answer

045

).

,

the S-register number, an equals sign (=), and a decimal

4.3.1 Examples of Assigning Values

1. Example: To assign longer pauses caused by the comma in a dial command—five seconds instead of

S8

two. Type ATS8=5 to assign 5 as the value for register
every comma in a dial command.

2. Example: To configure the modem to answer incoming calls after the thirtieth ring instead of after the first

S0

ring. Configure register

3. Example: International calls that take a long time to connect. The register
setting of 45 seconds is insufficient; the abort timer times out and cancels the call before a connection is
made. To change the
modem allows 10 more seconds for a carrier signal before aborting the call. The additional 10 seconds
should provide enough time for international calls.

with a value of 30, type ATS0=30 and press ENTER.

S7

value to 55 seconds, type ATS7=55 and press ENTER. Now, after dialing, the

. The modem will now pause five seconds for

S7

(abort timer) factory default

4.3.2 Examples of Reading Values

1. To verify that you entered the value correctly in the preceding examples, type ATS8? and press ENTER

in the first example, ATS0? in the second example, and ATS2? in the third example. You should receive
the responses

2. When configuring S-registers, it is a good practice to include the verification read command in the same
command string as the configuration assignment command. In the three preceding examples, type
ATS8=5S8?,

005, 030

ATS0=30S3?, and ATS7=55S7?, respectively.

, and

055

, respectively.

63

Chapter 4 - S-Registers

4.4 AT Commands Affecting S-Registers

For maximum throughput, the MT2834MR6's default configuration is for originating a call to another 33,600
bps modem that supports error correction, data compression, and flow control. If the receiving modem is not
compatible, the MT2834MR6 can match any ITU-T or Bell standard modem (but not proprietary protocols).

If you require a different configuration for your application, for example, if you want to use an MT2834MR6
modem strictly as an autoanswering device, or for service that does not support error correction, you can
selectively change the command parameters and S-register values in active memory and save the new

&W

values by using the
The

&W0

(or &W) command stores all current AT command and S-register values into nonvolatile random
access memory (NVRAM) and configures the modem so that it reads your custom settings in NVRAM when
the modem is turned on or when it is reset with the Z command. (The
the factory default settings in read-only memory [ROM] unless you also store the

3.) For convenience, you can incude the
in active memory, as in the following example:

&W1

The
causing the modem to read the factory default settings in ROM when it is subsequently turned on or reset.

For further information on how the &W command interacts with the reset commands, see Table 3-2.
Before you use the

L7

command erases your custom settings in NVRAM the next time the modem is turned off or reset,

commands.

command.

&F

reset command will continue to read

&F9

command. See Chapter

&W

command in the same command string that sets the new values

AT&E2$SP1#L3$R0$MB19200$SB115200$EB1S0=10&W0<CR>

&W

command, check the modem’s current operating parameters by using the L5, L6, and

64

Chapter 5 - Error Correction,

Data Compression & Speed Conversion

Chapter 5 - Error Correction, Data Compression, and Speed Conversion

5.1 Introduction

The MT2834MR6 has intelligent features beyond those of the AT command set described in Chapter 3. This
chapter describes high performance features and commands that provide error correction, data compression
and speed conversion capabilities. The remainder of this chapter describes these features and the
commands that implement them, as well as related commands.

The MT2834MR6’s error correction complies with the ITU-T V.42 standard. V.42 actually uses two error
correction protocols: LAP-M and MNP Class 3 & 4. MNP Class 3 & 4 error correction emerged as the industry
standard among modem manufacturers over the past decade. It is now in the public domain, and has been
implemented in dozens of modem brands with world wide installations in the hundreds of thousands of units.
LAP-M error correction is similar to MNP Class 3 & 4.

The MT2834MR6 provides two types of data compression: ITU-T V.42bis and MNP Class 5. V.42bis data
compression is newer; it requires concurrent LAP-M error correction. V.42bis is a very efficient data
compression technique that can provide up to 4-to-1 compression, depending on the type of data being
transmitted. MNP Class 5 data compression requires concurrent MNP Class 3 & 4 error correction. It is an
older and more established standard that offers data compression in the 2-to-1 range, which also depends
on the type of data being transmitted.

Speed conversion allows the modem to operate at one speed over the telephone lines and another speed at
the RS-232 serial port. This allows the computer or terminal to communicate with the modem at a fixed speed
of up to 115,200 bps, while the modem operates at various speeds up to 33,600 bps. Speed conversion is
vital if data compression is to be effective, since your terminal or computer must send data to the modem at a
higher speed than the modem is sending it over the phone line.

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5.2 How V.42 Detects and Corrects Errors

Some of the better known software-based error-correction protocols include Xmodem and Kermit (for
asynchronous file transfer software), X.PC (Tymnet’s asynchronous software protocol), and SDLC and HDLC,
two popular synchronous protocols common in the IBM mainframe environment. V.42 is functionally similar to
SDLC and HDLC, with some extras.

The main advantage of hardware-based V.42 error correction over these software-based protocols is in
throughput. Throughput is the effect that the use of the protocol has on the overall data rate. For example,
V.42 transmissions using a 2400 bps modem have an effective throughput of about 2600 bps. The same
modem using software-based X.PC would have an effective throughput of less than 2400 bps. Another way
of stating it is that V.42 has an efficiency of about 108%, while X.PC has an efficiency of about 91%.

Simply stated, one modem with V.42 sends coded data to another modem with V.42, and the receiving
modem is able to determine if there are any errors. If there are, the receiving modem tells the sending modem
to re-send the errant data until it’s correct.

Technically speaking, when using V.42, the sending modem uses a polynomial function to calculate a 16-bit
number that is a function of all the data sent in a particular message or block. It then sends those sixteen bits
at the end of the block, which can include up to 256 characters. The other V.42 modem, as it is receiving the
block, calculates its own version of the 16-bit number. Then it compares its number with the 16-bit number
sent with the block. If the numbers are the same, the block is free from errors. If the numbers are different, an
error has occurred somewhere in the block. That’s how errors are

detected

.
Once an error is detected, the receiving modem’s V.42 error
For all practical purposes, the result of the V.42 error correction protocol is error-free transmission. Using the

16-bit redundancy check, it will detect every error which is 16 bits or smaller with 100% probability. As a
result, the chances of an error occurring are actually so small that you can ignore them.

correction

is activated.

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5.3 Data Compression

The MT2834MR6 has both V.42bis and MNP class 5 data compression. ITU-T V.42bis is an international
data compression standard that can provide data compression of up to four to one in certain types of data.
MNP class 5 is a proprietary technique for data compression that provides a data compression capability of
two-to-one.

The MT2834MR6 must be in error correction mode before it can compress data (LAP-M error correction for

#L

V.42bis data compression or MNP error correction for MNP 5 data compression). By using the
you can select which error correction to use.

The type of file transfer protocol used to send and receive data has a big effect on the speed gain due to
compression. In general, a protocol that uses large data blocks transfers files quicker. For example,
YMODEM sends 1000 characters per block. It also helps to have the serial port of the receiving modem set to
the highest possible speed (115,200 bps), if the sending modem is set to a lower speed.

To achieve a data rate that is higher than the modem baud rate, turn Baud Adjust off (
serial port at a higher speed than the modem baud rate. For the MT2834MR6, set the serial port to 115,200
bps (

$SB115200

Data compression works by locating repeated strings of characters and repeating these strings using shorter
codewords. To use data compression, the modem must to be driven at full capacity. In other words, the data
must be present at enough volume and speed to get maximum compression benefits, as when using file
transfers or batch operations. Speed conversion must be on to operate the port at a higher speed than the
modem connection speed.

).

$BA0

command,

) and operate the

When operating the serial port at a higher speed than the modem baud rate, some type of flow control must

&E4

and

&E5

be used, otherwise data can be lost. (See
To enable data compression, type AT&E15 and press ENTER; to disable data compression, type AT&E14

and press ENTER.

Note: For data compression to take place, both the answer and the originate modems must have data
compression and error correction enabled.

commands.)

5.4 MNP Classes

The MNP protocol is divided into several classes. The classes you might encounter today in full duplex dial­up in 1200, 2400 and 9600 bps modems are Classes 3 through 5. When modems equipped with MNP start
communicating, they negotiate operation to the highest common MNP class between them and operate at
that level.

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5.5 V.42 Mode Select Command (#L)

The V.42 Mode Select command (#L) selects which type of error correction your MT2834MR6 will use for
transmissions. The V.42 standard implements both MNP Class 3 & 4 and LAP-M error correction protocols.
When you execute one of the
protocol. For example, the factory default setting (
the remote modem.

#L

commands, you instruct your MT2834MR6 how to operate with each

#L0

) tells your MT2834MR6 to negotiate the protocol with

The following sections detail the operation of the

#Ln

command.

5.5.1 #L0 Command

The #L0 command, which is the factory default, allows a pair of modems to negotiate which V.42 mode (MNP
or LAP-M) will be used.

5.5.1.1 Originate Mode

If both modems have LAP-M capability, the modems will use LAP-M mode. If one or both
modems do not have LAP-M capability and both have MNP, the modems will use the MNP.

5.5.1.2 Answer Mode

The answering modem will respond to either an MNP Link Request or a LAP-M ODP signal,
depending on which is issued by the originating modem.

5.5.2 #L1 Command

The #L1 command enables MNP error correction and disables LAP-M. This command is for originate mode
only. Answer mode still accepts MNP or LAP-M.

5.5.3 #L2 Command

The #L2 command enables LAP-M error correction and disables MNP. This command is for originate mode
only. Answer mode still accepts MNP or LAP-M.

5.5.4 #L3 Command

In the previous commands, the modems use a two-phase process to establish a V.42 connection (“Detection”
to establish whether the remote modem is also error correcting, and “Protocol Establishment” to determine
parameters and establish the error correction connection). If you know that the other modem is a V.42 error­correcting modem, and you wish to use LAP-M, use the #L3 command to disable the Detection phase and go
directly to Protocol Establishment. Both modems must have #L3 in effect.

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5.6 Modes of Operation

You can configure your MT2834MR6 in one of three different V.42 modes of operation, each with or without
compression. They are the non-error correction, reliable, and autoreliable modes. The modes and data
compression features are selected with commands described later in this chapter in “Compression, Error
Correction, Flow Control, Pass Through, and Pacing Commands.”

5.6.1 Non-Error Correction Mode (

In the non-error correction mode of operation, the MT2834MR6’s error correction capabilities are disabled,
and the modem functions as a non-error-correcting modem.

5.6.2 Reliable Mode (

In reliable mode, the MT2834MR6 uses its V.42 error correction capabilities during all transmissions. When
in reliable mode, the MT2834MR6 must be connected to a modem with a similar V.42 protocol activated
(MNP or LAPM). If the modems cannot establish a V.42 error correction connection, the MT2834MR6 will time
out and hang up.

5.6.3 Autoreliable Mode (

In autoreliable mode, the MT2834MR6 automatically determines, during the handshake at the start of the
online connection, whether or not the other modem is using error correction. If the MT2834MR6 determines
that the other modem is using V.42, it switches itself into the reliable (V.42) mode of operation. If it determines
that the other modem is not using V.42, the MT2834MR6 remains in non-error correction mode.

The MT2834MR6 uses a “Link Request” to determine whether the other modem is using V.42 error
correction. When the MT2834MR6 is in autoreliable mode and originates a call, it goes through normal
handshaking procedures. After establishing the online connection, the MT2834MR6 transmits a Link Request
message to the answering modem. If the answering modem replies with an appropriate V.42
acknowledgment response, the MT2834MR6 switches into reliable mode. Otherwise, it remains in non-error
correction mode. This V.42 handshake procedure generally takes about five seconds.

When operating in V.42 reliable mode, the MT2834MR6 stores data in a buffer as it is received. During
periods of error-caused retranmissions or compression slowdowns, this buffer may fill up. To prevent buffer
overflow and subsequent loss of data, the modem uses flow control to signal the computer attached to its RS­232 port that the modem buffer is close to being full. This causes the computer to pause in its data
transmission until the modem is able to empty its buffer sufficiently to accept more data, at which time the
modem signals the computer that it may resume transmission.

&E2

)

&E1

&E0

)

)

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5.7 Flow Control

Flow control refers to the techniques used by computer devices to stop and restart the flow of data from each
other. Flow control is necessary so that a device does not receive more data than it can handle. In the case of
the MT2834MR6, there is a need for flow control in both directions. Flow control for data passing from your
computer to the modem is called modem-initiated flow control, and flow control for data passing from the
modem to your computer is called computer/terminal-initiated pacing (see Figure 5-1).

The MT2834MR6 supports both hardware and software modem-initiated flow control and computer/terminal­initiated pacing. It also supports Hewlett Packard ENQ/ACK pacing. The MT2834MR6 can allow hardware
and software pacing to be passed through the modem to the other end of the link so that your computer or
terminal can control data start/stop activity through your modem. This is called “XON/XOFF pass-through".

To put it simply, flow control is something the modem does to the computer, while pacing is something the
computer does to the modem.

Figure 5-1. Flow control and pacing

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5.8 Modem-Initiated Flow Control

When operating in V.42 reliable mode, the MT2834MR6 stores data in a buffer as it is received. During
periods of error-caused retransmissions or compression slowdowns, this buffer may fill up. To prevent buffer
overflow and subsequent loss of data, the modem uses flow control to signal the computer attached to its RS­232 port that the modem buffer is close to being full. This causes the computer to pause in its data
transmission until the modem is able to empty its buffer sufficiently to accept more data, at which time the
modem signals the computer that it may resume transmission.

The MT2834MR6 can use either of two methods of modem-initiated flow control: software flow control, which
uses special XON and XOFF characters in the data transmissions, and hardware flow control, which uses the
CTS output on the RS-232 interface. Most terminals and computers support one or both of these methods.

5.8.1 XON/XOFF Flow Control (

In this method, control characters known as XON and XOFF are inserted by the modem into the flow of data
from the serial port. XOFF (CTRL-S), stops the flow of data, and XON (CTRL-Q), restarts it. XOFF/XON flow
control is not recommended for binary data, because an XOFF character could be part of the data, and would
halt data flow.

5.8.2 Hardware Flow Control (

With hardware flow control, the modem uses the RS-232 interface to control the flow of data on the serial port.
The CTS (Clear to Send) signal on Pin 5 of the RS-232 interface is brought low to stop the flow of data, and is
brought high to restart it.

When you select hardware flow control as your flow control method, you select it also for pacing. The
difference between the two is that flow control uses the CTS output signal, while pacing uses the RTS input
signal.

&E5

&E4

)

)

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Chapter 5 - Error Correction, Data Compression, and Speed Conversion

5.9 Pacing (

As mentioned earlier, the MT2834MR6 can initiate flow control by issuing XON/XOFF commands or by
toggling the CTS signal on the RS-232 interface. The modem can also be configured to react to similar
commands and signals from the computer or terminal to which it is connected by the RS-232 interface.

Pacing is computer-initiated flow control. When pacing is enabled on the modem, the modem responds to the
terminal or computer pacing. When pacing is disabled on the modem, the modem ignores pacing.

Before you enable pacing on the MT2834MR6, you must select a flow control method. When pacing is
enabled, the MT2834MR6 responds either to XON/XOFF commands, or to the toggling of the RTS (Request
to Send) signal on Pin 4 of the RS-232 interface, depending on what you selected as your flow control
method.

5.9.1 XON/XOFF Pass-Through (

So far, you have had three choices to make regarding pacing. You can set the modem to respond to XON/
XOFF pacing, or to respond to RTS pacing, or you can set the modem to ignore pacing completely.

Another choice you can make (which actually can apply to both pacing and flow control, although it applies
mainly to pacing) is XON/XOFF pass-through. If your modem is set to respond to XON/XOFF commands, you
can have the modem do one of the following.

a. The modem responds to the XON and XOFF pacing commands while at the same time allowing

these commands to pass through the modem and on to the remote location. We call this
“respond, pass-through.”

b. The modem responds to XON/XOFF pacing, but does not allow the pacing signals to pass

through the modem and on to the remote location. We call this “respond, no pass-through.”

When XON and XOFF commands are allowed to pass through the modem, the computer at the remote site
receives these commands, and depending on how it is configured, the computer may respond to them also.

&E13

)

&E7

)

5.9.2 Non-Error Correction Mode Flow Control (

You can use XON/XOFF to control the flow of data between two MT2834MR6s that are connected in non­error correction mode. Disable or enable this method of flow control by using the Non-Error Correction Mode
Flow Control commands. When the modems are connected in reliable mode, a different method of modem
flow control is used, and the commands for non-error correction mode flow control are ignored.

You must enable non-error correction mode flow control if you use speed conversion in non-error correction
mode.

5.9.3 Hewlett Packard ENQ/ACK Pacing (

If the MT2834MR6 is used with Hewlett Packard or similar equipment that employs ENQ/ACK pacing, you
can configure it to respond to the ENQ/ACK commands used by Hewlett Packard systems. Doing so does not
effect any other flow control or pacing already configured in the modem.

When the MT2834MR6 is configured for ENQ/ACK, the ENQ (Ctrl-E) and ACK (Ctrl-F) signals from the HP
equipment will be accepted and responded to according to the Hewlett Packard protocol.

&E9

)

&E10

and

&E11

)

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Chapter 5 - Error Correction, Data Compression, and Speed Conversion

5.10 Compression, Error Correction, Flow Control,

and Pacing Commands

The MT2834MR6 has several commands that control error correction, data compression, and flow control:

5.10.1 V.42 Error Correction Modes

&E0 Non-auto correction mode (no error correction).
&E1 Autoreliable mode (factory default).
&E2 Reliable mode.

5.10.2 Modem-Initiated Flow Control

&E3 Disable flow control.
&E4 CTS/RTS hardware flow control (factory default).
&E5 XON/XOFF software flow control.

5.10.3 XON/XOFF Pass-Through

&E6 Respond to and discard XON/XOFF characters when &E5 is selected (factory

default).

&E7 Respond to and pass through XON/XOFF characters when &E5 is selected.

5.10.4 Hewlett Packard ENQ/ACK Pacing

&E8 Ignore ENQ/ACK pacing characters (factory default).
&E9 Respond to ENQ/ACK pacing characters.

5.10.5 Non-Error Correction Mode Flow Control

&E10 Non-error correction mode flow control off (factory default).
&E11 Non-error correction mode flow control on.

5.10.6 Pacing (Computer-Initiated Flow Control)

&E12 Pacing off.
&E13 Pacing on (factory default).

5.10.7 Data Compression

&E14 Data Compression disabled.
&E15 Data Compression enabled.*

* The factory default setting for data compression is enabled, but the modem will not compress data unless

(autoreliable mode) or

&E2

(reliable mode) is also selected.

&E1

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Chapter 5 - Error Correction, Data Compression, and Speed Conversion

5.11 Result Codes

When the MT2834MR6 connects with another modem with error-correction or data compression enabled, its

CONNECT

result codes.)

5.11.1 MNP Error Correction

If terse responses are enabled, an R is added to the numeric code. If verbose responses are enabled, the
word

5.11.2 LAP-M Error Correction

If terse responses are enabled, an L is added to the numeric code. If verbose responses are enabled, the
word

5.11.3 Data Compression

If terse responses are enabled, a C is added to the numeric code. If verbose responses are enabled, the
word

responses change to inform you of the type of connection. (See Appendix C for a complete list of

RELIABLE

LAPM

COMPRESSED

follows the

follows the

CONNECT

CONNECT

follows the

message.

message.

CONNECT

message.

5.12 Speed Conversion

Speed conversion allows the MT2834MR6 to communicate at one speed over the phone line, and at another
speed at the RS-232 interface. The speed (baud rate) of the RS-232 interface, in bits per second (bps) can be
fixed independently of the speed of the online transmissions.

Besides data compression, another popular application for speed conversion involves an autoanswer
MT2834MR6 connected to a computer that does not have autobauding capability. This means that the
computer must be set at a fixed baud rate, regardless of whether the modem is communicating over the
phone line at 300, 1200, 2400, 4800, 9600, 14,400, 19,200, 21,600, 24,000, 26,400, or 28,800 bps. In this
application, speed conversion allows the modem to match its speed to that of a calling modem, while at the
same time communicating with the attached computer through its RS-232 serial port at a fixed baud rate,
which can be preselected at 300, 1200, 2400, 4800, 9600, 19,200, 38,400, 57,600, or 115,200 bps.

The flow control and pacing methods used between the computer and the modem during speed conversion
are the same as those used with V.42 error correction. The two choices (XON/XOFF or RTS/CTS) are
selected by using the &E commands detailed earlier in this chapter. If you are not using the modem’s V.42
error correction, you must activate modem flow control with a separate command (&E11), as explained
earlier.

There are three commands that relate specifically to speed conversion. They are the Baud Adjust ($BA),
Modem Baud Rate ($MB) and Serial Port Baud Rate ($SB) commands.

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Chapter 5 - Error Correction, Data Compression, and Speed Conversion

5.12.1 Baud Adjust (

In typical operations, the MT2834MR6 will do one of two things regarding speed. It will automatically match
the speed of its RS-232 interface and phone line transmissions to that of the terminal or computer to which it
is connected as soon as it receives its first AT command. Or, in autoanswer mode, it will match its RS-232
and transmission speeds to that of the originating modem that called it. This is typical of many dial-up
modems, and it is referred to variously as

When you enable speed conversion, the modem does not adjust its speed at the RS-232 serial port, even if
the modem does adjust its line transmission speed. To turn baud adjust off and speed conversion on, type

AT$BA0

Note: Even though baud adjust sounds like it should mean the same thing as speed conversion, it actually
means the opposite.

To turn baud adjust on and speed conversion off, type AT$BA1 and press ENTER. The modem will now
match its RS-232 speed to that of the computer, and will adjust its speed to any changes in the computer’s
speed in the originate mode, or to the speed of the originating modem when it’s in the answer mode. With
baud adjust on, the speed at which the modem communicates over the phone line is always the same as the
speed at which it communicates via its RS-232 serial port.

(where the 0 is a zero).

a. Turning baud adjust
b. Turning baud adjust

$BA

)

auto-speed

off

turns speed conversion on.

on

turns speed conversion

or

baud adjust

. Multi-Tech uses the term

off

.

baud adjust

.

5.12.2 Modem Baud Rate ($MB)

The $MB command presets the MT2834MR6’s transmission rate for originate operations, i.e., the speed of
the modem’s transmissions over the telephone lines when originating a call. With speed conversion, this
transmission speed can be a different rate than the serial port speed.

When the MT2834MR6 receives a call from another modem, it automatically switches its phone line
transmission rate to match the calling modem. However, if the MT2834MR6 originates a call to another
modem that is unable to connect at the speed of the MT2834MR6, the MT2834MR6 will automatically drop to
a lower speed in an attempt to match the speed of that modem. For example, if the MT2834MR6 is set for
28,800 bps and calls another modem that has a top speed of 9600 bps, it will drop to 9600 bps.

When baud adjust is on ($BA1), speed conversion is off, as we discussed earlier. In that case, the $MB
command is ignored, since it is part of speed conversion.

To set the Modem Baud Rate, type AT$MBn, where n is the desired rate.

AT$MB75 ITU-T V.23 AT$MB300 300 bps
AT$MB1200 1200 bps AT$MB2400 2400 bps
AT$MB4800 4800 bps AT$MB9600 9600 bps
AT$MB14400 14,400 bps AT$MB16800 16,800 bps
AT$MB19200 19,200 bps AT$MB28800 28,800 bps
AT$MB33600 33,600 bps (factory default)

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5.12.3 Serial Port Baud Rate ($SB)

The $SB command presets the speed of the MT2834MR6’s RS-232 serial port in both the originate and the
answer modes. Speed conversion allows you to set this serial port baud rate at a fixed speed of up to
115,200 bps, regardless of the modem’s transmission speed setting.It also sets the default speed at which
the modem issues command responses (result codes).

For this command to work, the modem’s baud adjust feature must be turned off with the $BA command.
The MT2834MR6 will accept AT commands at any speed, regardless of the speed preset by the $SB

command. If the modem receives such a command at a speed that is different from the preset speed, the
modem switches its serial port baud rate to match the new AT command speed, although the baud rate value
stored by the $SB command remains the same. This provides you with a convenient way to switch the serial
port speed, while still making it easy to automatically return to the original speed the next time the modem is
powered up, or reset using the ATZ command.

To set the serial port baud rate, type AT$SBn, where n can be 300, 1200, 2400, 4800, 9600,19,200, 38,400,
57,600, or 115,200 bps as listed below:

AT$SB300 300 bps AT$SB1200 1200 bps
AT$SB2400 2400 bps AT$SB4800 4800 bps
AT$SB9600 9600 bps AT$SB19200 19200 bps
AT$SB38400 38400 bps AT$SB57600 57,600 bps
AT$SB115200 115,200 bps (factory default)

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Chapter 5 - Error Correction, Data Compression, and Speed Conversion

5.13 Related Commands

5.13.1 Autoreliable Buffering ($A)

In autoreliable mode, the modem is given four seconds to establish a reliable connection. If it cannot
establish a reliable connection in that time, the modem drops to non-error correction mode. Any data
received during this period is normally discarded. The $A command is used to cause the modem to buffer
(save) data that is received during the autoreliable time-out period. This data is then output by the modem
after it sends the CONNECT message.

Type AT$A0 to discard data received during the autoreliable time period (factory default).
Type AT$A1 to buffer data received during the autoreliable time period.

5.13.2 Maximum Block Size (&BS)

The maximum size of reliable mode data blocks is controlled by the &BS command. MNP Class 3 sends
blocks of 1 to 64 characters. MNP Classes 4 and 5 normally send blocks of 1 to 256 characters. Reducing the
block size for Classes 4 and 5 to 64 characters may give a smoother flow of data, and improve throughput
performance on noisy phone lines. Using smaller block sizes over good phone lines may cause a slight loss
in data throughput.

Type AT&BS0 for a maximum transmit block size of 64 characters.
Type AT&BS1 for a maximum transmit block size of 256 characters (factory default).

5.13.3 Autoreliable Fallback Character ($F)

In autoreliable mode, the modem is given four seconds to establish a reliable connection. If a single carriage
return character, <CR>, is received from the remote modem during this four second period, the autoreliable
modem assumes that the remote modem is not in reliable mode and drops to a non-error correction mode.
The carriage return character is then output following the CONNECT message. The carriage return character
is the only character that causes the modem to drop to non-error correction mode. Any other data is either
buffered or discarded.

Use the $F command to disable this fallback feature. The autoreliable fallback character ($F) and the auto
reliable buffering ($A) commands can be used together to cause the modem to buffer all data received up to
the carriage return and then drop to non-error correction mode. All data received will then be output following
the CONNECT message.

Type AT$F0 to cause the modem not to fall back to non-error correction mode if a carriage return character is
received.

Type AT$F1 to cause the modem to fall back to error correction mode if a carriage return character is
received (factory default).

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Chapter 5 - Error Correction, Data Compression, and Speed Conversion

5.13.4 Retransmit Count ($R)

If errors are received during a reliable connection, the modem resends the block of data that contained
errors. If another error occurs, the block is re-sent again. The modem counts the number of times that a data
block is re-sent. If the same block of data is re-sent 12 times and still has not been received properly, the
modem aborts the connection, as dictated by the AT$R0 command.

This retransmit counter can be disabled with the $R1 command. When the retransmit counter is disabled, the
modem keeps trying to send data and will not abort, not matter how many times the same block is re-sent.

Type AT$R0 to disconnect if the retransmit count is exceeded (factory default).
Type AT$R1 to not disconnect because of excessive retransmits.

5.13.5 V.42 Error Correction at 300 bps ($E)

At 300 bps, error correction is not normally used.

&E0

correction (
setting, disables V.42 error correction at 300 bps altogether.

), autoreliable (

&E1

) or reliable (

$E1

lets the MT2834MR6 function in either non-error

&E2

) mode at 300 bps.

$E0

, which is the factory default

5.14 Summary

V.42 error correction is built into the MT2834MR6’s hardware, and detects virtually 100 percent of
transmission errors, which are usually caused by noisy phone lines. When errors are detected, the V.42
protocol causes the modem to retransmit the errant data block.

V.42bis and MNP data compression, also built into the MT2834MR6’s hardware, provides an effective
throughput higher than the modem’s transmission speed. The amount of increase depends on the type of
data being transmitted.

The MNP protocol is divided into several classes, which for our purposes are numbered 3 through 5. The
MT2834MR6 uses all of these MNP classes, which yields higher throughput and error-free transmissions.
LAP-M provides another type of error correction.

The MT2834MR6 can be set for three different modes of operation. Non-error correction mode disables error
correction, reliable mode enables it, and autoreliable mode allows the modem to automatically turn V.42 on
when it detects its use in another modem.

Flow control methods are used by the MT2834MR6 to prevent data loss from buffer overflow. The modem can
both initiate it (flow control) and respond to it (pacing), using either XON/XOFF commands or RS-232
signaling via the serial port’s CTS and RTS signals. Hewlett Packard ENQ/ACK pacing is also supported. If
needed, XON/XOFF commands can be “passed through” the modem to a remote computer or terminal.

Speed conversion allows the MT2834MR6 to operate at one speed over the telephone lines and another
speed at the RS-232 serial port, allowing the computer or terminal to communicate with the modem at a fixed
speed of up to 115,200 bps, while the modem operates at various speeds up to 33,600 bps. This ability is for
data compression, since your terminal or computer must present data to the modem at a higher speed than
the modem sends it over the phone line.

79

Chapter 6 - Testing & Troubleshooting

Chapter 6 - Testing and Troubleshooting

6.1 Introduction

Each time you power up the MT2834MR6, it performs an automatic self-test to ensure proper operation. The
MT2834MR6 also has three diagnostic tests: local analog loopback, digital loopback (remote/automatic), and
digital loopback (local/manual). These ITU-T V.54 loopback tests isolate telephone circuit and transmission
problems.

In a loopback test, data from your computer loops through the circuits of your modem and/or a remote modem
before it appears on your monitor. When the loop has been completed, the data on your PC’s monitor should
match the original data.

The local analog loopback test allows you to verify that the modem’s transmitter and receiver circuits are
functioning properly.

The local digital loopback allows you to verify that the local computer or terminal, the two modems, and the
transmission line between them are functioning properly.

The remote digital loopback test allows you to verify that the remote computer or terminal, the remote modem,
the serial ports, the telephone line, and the local modem are functioning properly.

Note: Loopback tests operate at all speeds except 300 bps.

Other tests are initiated with the MultiModemManager software, as explained in the MultiModemManager
Owner's Manual.

81

Chapter 6 - Testing and Troubleshooting

6.2 Local Analog Loopback Test (V.54 Loop 3)

In this test, data from your computer or terminal is sent to your modem’s transmitter, converted into analog
form, looped back to the modem’s receiver, converted into digital form, and then sent to your monitor for
verification. No connection to the phone line is required. See Figure 6-1.

Figure 6-1. Local analog loopback test.

6.2.1 Test Procedure

1. Connect the modem to your computer. Using your communication software, set the desired baud rate.

2. Type ATU or ATU0 and press ENTER. This places your modem in analog loopback mode in the

originate mode. A
command mode and in a pseudo-online mode.

3. Note that the CD LED is on. If you’re set for 14,400 bps or higher, the Speed LED should be on. If the CD

LED is not on, there is a defect in your modem.

4. Enter characters from your keyboard. For this test, typing multiple uppercase

to send an alternating test pattern of binary ones and zeros. The characters entered should be displayed
on your monitor. The TD and RD LEDs should flash when a character is entered.

5. For a more complete test, you should also test the modem in answer mode. To do this, you must first

terminate the originate mode by entering an escape sequence (+++AT<CR> or <BREAK>AT<CR>). An

OK

should appear on your display. Then type ATU1 and press ENTER to place the modem in analog

loopback in answer mode.

6. Note that the CD LED is on. If you’re set for 14,400 bps or higher, the Speed LED should be on. If the CD

LED is not on, there is a defect in your modem.

7. Enter characters from your keyboard. Type multiple uppercase

pattern of binary ones and zeros. The characters entered should be displayed on your monitor. The TD
and RD LEDs should flash when a character is entered.

8. To exit the test, enter an escape sequence (+++AT<CR> or <BREAK>AT<CR>), which returns the

modem to command mode.

9. Your modem passes this test if the data received on your monitor are the same as the data entered from

your keyboard. If different data appear on your monitor, your modem is probably causing the problem,
though it could also be your computer. If your modem passes this test, but you are receiving errors while
on line, the remote modem or the phone line could be at fault.

CONNECT

message should appear on your display. The modem is now out of

U

characters is a good way

U

characters to send an alternating test

82

Chapter 6 - Testing and Troubleshooting

6.3 Remote Digital Loopback Test (V.54 Loop 2)

In this test, your modem must be online with another modem, such as another ZDX, that is set up to respond
to a request for remote digital loopback. With the ZDX, this ability to respond is controlled by the &T
command. AT&T4 enables the response to remote digital loopback; AT&T5 disables the response. The
modem defaults to &T5 on power-up, so this must be changed on the remote modem before initiating remote
digital loopback.

Initiate remote digital loopback with the ATU2 command, which places the remote modem in digital loopback
mode. Data from your computer or terminal are transmitted through your modem and over the phone line to
the remote modem, where they are then looped back to your modem. See Figure 6-2.

Figure 6-2. Remote digital loopback test.

6.3.1 Test Procedure

1. Arrange to have &T4 set on the remote test modem.

2. Open your communications software and go into terminal mode. Type AT and press ENTER; you should

get an OK message. Type AT&E0<CR> to disable error correction.

3. Dial the remote modem and establish your online connection.

4. Type the escape sequence (+++AT<CR> or <BREAK>AT<CR>) to bring your modem into command

mode while maintaining the connection with the remote modem.

5. Type ATU2 and press ENTER. The local modem responds to this command by transmitting an

unscrambled marking signal, which causes the remote modem to place itself in digital loopback mode.
Then the local modem exits command mode and enters online mode.

U

6. Enter data from your keyboard. For this test, typing multiple uppercase

send an alternating test pattern of binary ones and zeroes. Data received by the remote modem enters
its analog receiver, is converted to digital data, is reconverted into analog, and then is transmitted back to
your modem. Your modem passes this test if the data received on your monitor is the same as the data
entered from your keyboard.

7. To exit the test, enter an escape sequence (+++AT<CR> or <BREAK>AT<CR>), which returns the

modem to command mode. The modem should respond with an
with the remote modem for normal data transmission, type ATO and press ENTER. If you wish to
terminate the call, type ATH and press ENTER to hang up.

OK

characters is a good way to

message. If you wish to stay on line

83

Chapter 6 - Testing and Troubleshooting

6.4 Local Digital Loopback Test (V.54 Loop 2)

This test is identical to the remote digital loopback test with one exception. Instead of using your modem to
signal a remote modem to place itself in digital loopback mode, your modem is placed in digital loopback
mode while the remote modem is not. Data is entered and transmitted from the remote modem, sent across
the phone line to the local modem, and looped back to the remote modem. See Figure 6-3.

Figure 6-3. Local digital loopback test

6.4.1 Test Procedure

1. Open your communications software and go into terminal mode. Type AT and press ENTER; you should

get an

OK

message. Enter AT&E0<CR> to disable error correction.

2. Dial the remote modem and establish your online connection.

3. Type an escape sequence (+++AT<CR> or <BREAK>AT<CR>) to bring your modem into command

mode while still maintaining the connection with the remote modem.

OK

4. Type ATU3 and press ENTER. Once you receive an

enabled), your modem is placed in digital loopback mode.

5. Have someone enter data from the remote keyboard. For this test, typing multiple uppercase

characters is a good way to send an alternating test pattern of binary ones and zeros. The data received
by your modem enters its analog receiver, is converted to digital data, is reconverted into analog, and
then is transmitted back to the remote modem. Your modem passes this test if the data received on the
remote monitor is the same as the data entered from the remote keyboard.

6. To exit the test, enter an escape sequence (+++AT<CR> or <BREAK>AT<CR>), which returns the

modem to command mode. The modem should respond with an
with the remote modem for normal data transmission, type ATO and press ENTER. If you wish to
terminate the call, type ATH and press ENTER to hang up.

message from your modem (if responses are

U

OK

message. If you wish to stay on line

84

Chapter 7 - Warranty & Service

Chapter 7 - Warranty And Service

7. 1 Multi-Tech Systems, Inc. Warranty & Repairs Policies

7.1.1 Warranty

Multi-Tech Systems, Inc., (hereafter “MTS”) warrants that its products will be free from defects in material or
workmanship for a period of two, five, or ten years (depending on model) from date of purchase, or if proof of
purchase is not provided, two, five, or ten years (depending on model) from date of shipment.

MTS MAKES NO OTHER WARRANTY, EXPRESS OR IMPLIED, AND ALL IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE HEREBY DISCLAIMED.

This warranty does not apply to any products which have been damaged by lightning storms, water, or power
surges or which have been neglected, altered, abused, used for a purpose other than the one for which they
were manufactured, repaired by Customer or any party without MTS’s written authorization, or used in any
manner inconsistent with MTS’s instructions.

MTS’s entire obligation under this warranty shall be limited (at MTS’s option) to repair or replacement of any
products which prove to be defective within the warranty period or, at MTS’s option, issuance of a refund of
the purchase price. Defective products must be returned by Customer to MTS’s factory – transportation
prepaid.

MTS WILL NOT BE LIABLE FOR CONSEQUENTIAL DAMAGES, AND UNDER NO CIRCUMSTANCES WILL
ITS LIABILITY EXCEED THE PRICE FOR DEFECTIVE PRODUCTS.

7.1.2 U.S. and Canadian Customers

In the event that service is required, products may be shipped, freight prepaid, to our Mounds View,
Minnesota, factory:

Multi-Tech Systems, Inc.
2205 Woodale Drive
Mounds View, MN 55112
Attn: Repairs, Serial #______

A Returned Materials Authorization (RMA) is not required. Return shipping charges (surface) will be paid by
MTS. Please include inside the shipping box a description of the problem, a return shipping address (must
have street address, not P.O. Box), a telephone number, and if the product is out of warranty, a check or
purchase order for repair charges.

For out of warranty repair charges, go to:
agreements are available for selected products. Please call MTS at 888 288-5470, extension 5308, or visit
our web site at

Please direct your questions regarding technical matters, product configuration, verification that the product
is defective, etc., to our Technical Support department at 800 972-2439 or e-mail
Please direct your questions regarding repair expediting, receiving, shipping, billing, etc., to our Repair
Accounting department at 800 328-9717 or [phone], or e-mail

Repairs for damages caused by lightning storms, water, power surges, incorrect installation, physical abuse,
or user-caused damages are billed on a time-plus-materials basis.

www.multitech.com

www.multitech.com.

for details on rates and coverages.

Extended two-year overnight replacement

[e-mail].

[e-mail]

.

86

Chapter 7 - Warranty And Service

7.1.3 International Customers (outside U.S.A. and Canada)

Your original point of purchase reseller may offer the quickest and most economical repair option for your
Multi-Tech product. You may also contact any Multi-Tech sales office for information about the nearest
distributor or other repair service for your Multi-Tech product:

In the event that factory service is required, products may be shipped, freight prepaid, to our Mounds View,
Minnesota, factory. Recommended international shipment methods are via Federal Express, UPS or DHL
courier services, or by airmail parcel post; shipments made by any other method will be refused. A Returned
Materials Authorization (RMA) is required for products shipped from outside the U.S.A. and Canada. Please
contact us for return authorization and shipping instructions on any international shipments to the U.S.A.

Please include inside the shipping box a description of the problem, a return shipping address (must have
street address, not P.O. Box), your telephone number, and if the product is out of warranty, a check drawn on
a U.S. bank or your company’s purchase order for repair charges. Repaired units will be shipped freight
collect, unless other arrangements are made in advance.

Please direct questions regarding technical matters, product configuration, verification that the product is
defective, etc., to our Technical Support department nearest you, as listed at

COMPANY/offices/DEFAULT.ASP

questions regarding repair expediting, receiving, shipping, billing, etc., to our Repair Accounting department
at [phone] in the U.S.A., or e-mail

Repairs for damages caused by lightning storms, water, power surges, incorrect installation, physical abuse,
or user-caused damages are billed on a time-plus-materials basis.

., or e-mail

[e-mail]

[e-mail]

www.multitech.com

http://www.multitech.com/

. When calling the U.S., please direct

.

.

7.1.4 International Distributors

Procedures for international distributors of Multi-Tech products are on the Distributor Web site at

www.multitech.com/PARTNERS/login/

.

http://

87

Chapter 7 - Warranty And Service

7.2 Repairs

7.2.1 Repair Procedures for U.S. and Canadian Customers

In the event that service is required, products may be shipped, freight prepaid, to our Mounds View,
Minnesota factory:

Multi-Tech Systems, Inc.
2205 Woodale Drive
Mounds View, MN 55112
Attn: Repairs, Serial # ____________

A Returned Materials Authorization (RMA) is not required. Return shipping charges (surface) will be paid by
MTS. Please include, inside the shipping box, a description of the problem, a return shipping address (must
have street address, not P.O. Box), your telephone number, and if the product is out of warranty, a check or
purchase order for repair charges. For out of warranty repair charges, go to

Extended two-year overnight replacement service agreements are available for selected products. Please
call MTS at [phone], extension 5308 or visit our web site at: www.multitech.com for details on rates
and coverages.

Please direct your questions regarding technical matters, product configuration, verification that the product
is defective, etc., to our Technical Support department at [phone] or email
Please direct your questions regarding repair expediting, receiving, shipping, billing, etc., to our Repair
Accounting department at [phone] or [phone], or email [e-mail].

www.multitech.com

[e-mail].

Repairs for damages caused by lightning storms, water, power surges, incorrect installation, physical abuse,
or user-caused damages are billed on a time-plus-materials basis.

7.2.2 Repair Procedures for International Customers

Your original point of purchase Reseller may offer the quickest and most economical repair option for your
Multi-Tech product. You may also contact any Multi-Tech sales office for information about the nearest
distributor or other repair service for your Multi-Tech product. Visit our website at: www.multitech.com

In the event that factory service is required, products may be shipped, freight prepaid to our Mounds View,
Minnesota factory. Recommended international shipment methods are via Federal Express, UPS or DHL
courier services, or by airmail parcel post; shipments made by any other method will be refused. A Returned
Materials Authorization (RMA) is required for products shipped from outside the U.S.A. and Canada. Please
contact us for return authorization and shipping instructions on any International shipments to the U.S.A.
Please include, inside the shipping box, a description of the problem, a return shipping address (must have
street address, not P.O. Box), your telephone number, and if the product is out of warranty, a check drawn on
a U.S. bank or your company’s purchase order for repair charges. Repaired units shall be shipped freight
collect, unless other arrangements are made in advance.

Please direct your questions regarding technical matters, product configuration, verification that the product
is defective, etc., to our Technical Support department nearest you or email
calling the U.S., please direct your questions regarding repair expediting, receiving, shipping, billing, etc., to
our Repair Accounting department at: +[phone] in the U.S.A., or email [e-mail].

Repairs for damages caused by lightning storms, water, power surges, incorrect installation, physical abuse,
or user-caused damages are billed on a time-plus-materials basis.

[e-mail]. When

88

Chapter 7 - Warranty And Service

7.2.3 Repair Procedures for International Distributors

Procedures for International Distributors of Multi-Tech products are on the distributor web site:
www.multitech.com

7.2.4 Replacement Parts

SupplyNet, Inc., can supply you with replacement power supplies, cables and connectors for selected Multi­Tech products. You can place an order with SupplyNet via mail, phone, fax or the Internet at the following
addresses:

Mail: SupplyNet, Inc.

614 Corporate Way
Valley Cottage, NY 10989

Phone: [phone]
Fax: [phone]
Email:
Internet:

[e-mail]
http://www.thesupplynet.com

7.3 Technical Support

Multi-Tech Systems has an excellent staff of technical support personnel available to help you get the most
out of your Multi-Tech product. If you have any questions about the operation of this unit, please call 800 972­2439 (USA and Canada) or 763 785-3500 (international and local). Please have modem information
available. You can also contact Technical Support by e-mail at the following addresses:

Country Email Telephone

U.S.A., Canada
France:
India:
U.K.:
Rest of world:

Please note the status of the modem before contacting Technical Support. Status information can include the
state of the LED indicators, screen messages, diagnostic test results, problems with a specific application,
etc.

[e-mail]
[e-mail]
[e-mail]
[e-mail]
[e-mail]

800 972-2439
+(33) 1-64 61 09 81
[phone]
+(44) 118 959 7774
[phone]

7. 4 Internet Site

Multi-Tech is a commercial provider on the Internet. Multi-Tech has a Web site at:

www.multitech.com

.

89

Appendices

Appendix A

ASCII Conversion Chart

CTRL CODE HEX DEC CODE HEX DEC CODE HEX DEC CODE HE X DEC

@ NUL 00 0 SP 20 32 @ 40 64 ` 60 96

A SOH 01 1 ! 21 33 A 41 65 a 61 97
B STX 02 2 " 22 34 B 42 66 b 62 98
C ETX 03 3 # 23 35 C 43 67 c 63 99
D EOT 04 4 $ 24 36 D 44 68 d 64 100
E ENQ 05 5 % 25 37 E 45 69 e 65 101
F ACK 06 6 & 26 38 F 46 70 f 66 102
G BEL 07 7 ' 27 39 G 47 71 g 67 103
H BS 08 8 ( 28 40 H 48 72 h 68 104

I HT 09 9 ) 29 41 I 49 73 i 69 105

J LF 0A10 * 2A42 J 4A74 j 6A106
K VT 0B11 + 2B43 K 4B75 k 6B107
L FF 0C12 , 2C44 L 4C76 l 6C108
MCR 0D13 - 2D45 M 4D77 m 6D109
N SO 0E14 . 2E46 N 4E78 n 6E110
O SI 0F15 / 2F47 O 4F79 o 6F111
P DLE 10 16 0 30 48 P 50 80 p 70 112
Q DC1 11 17 1 31 49 Q 51 81 q 71 113
R DC2 12 18 2 32 50 R 52 82 r 72 114
S DC3 13 19 3 33 51 S 53 83 s 73 115
T DC4 14 20 4 34 52 T 54 84 t 74 116
U NAK 15 21 5 35 53 U 55 85 u 75 117
V SYN 16 22 6 36 54 V 56 86 v 76 118

W ETB 17 23 7 37 55 W 57 87 w 77 119

X CAN 18 24 8 38 56 X 58 88 x 78 120
Y EM 19 25 9 39 57 Y 59 89 y 79 121
Z SUB 1A 26 : 3A 58 Z 5A 90 z 7A 122

[ ESC 1B 2 7 ; 3B 59 [ 5B 91 { 7B 123
\ FS 1C28 < 3C60 \ 5C92 | 7C124
] GS 1D29 = 3D61 ] 5D93 } 7D125

^ RS 1E30 > 3E62 ^ 5E94 ~ 7E126
_ US 1F31 ? 3F63 _ 5F95 DEL7F127

Appendix

NUL Null, or all zeros VT Vertical Tab SY N Sync.
SOH Start of Header FF Form Feed ETB End Transmission Block
STX Start of Text CR Carriage Return CAN Cancel
ETX End of Text SO Shift Out EM End of Medium
EOT End of Transmission SI Shift In SUB Substitute
ENQ Enquiry DLE Data Link Escape ESC Escape
ACK Acknowledge DC1 Device Control 1 FS File Separator
BEL Bell or Alarm DC2 Device Control 2 GS Group Separator
BS Backspace DC3 Device Control 3 RS Record Separator
HT Horizontal Tab DC4 Device Control 4 US Unit Separator
LF Line Feed NAK Negative Acknowledge DEL Delete

91

Appendix

Appendix B

Dial Pulses

When you pulse dial, as when you make a call with a rotary dial telephone, your telephone or modem
generates codes in the form of pulses that simulate the opening and closing of old-fashioned electric relays,
or switches. The number of pulses in a code are the same as the digit they encode; thus, the digit 1 is

2

represented by one pulse, the digit
the digit
ms, and B is either 40 or 33 ms, for a total of 100 ms per cycle, or a rate of 10 pulses per second. The
interdigital pause time is 800 ms. The pulse ratios are controlled by the

1

. Each pulse consists of an A ms open (break) and a B ms closed (make), where A is either 60 or 67

by two pulses, etc. In Figure B-1, the digit 2 is pulse dialed, followed by

&P

command.








  

Figure B-1. Dial pulses

92

Appendix

Tone Dial Frequencies

The tone dialing method combines two frequencies for each of the twelve digits found on a touch-tone dial
pad. This method is referred to as dual-tone multi-frequency (DTMF) dialing.

The four horizontal rows on a touch-tone keypad use four low-frequency tones (697, 770, 852, 941 Hz), while
the three vertical columns use three high-frequency tones (1209, 1336, 1477 Hz). The tone frequency
tolerance is ± 0.02%.

For example, the digit 4 is dialed by combining two tone frequencies: 770 Hz from the second row, and 1209
Hz from the first column. In another example, the digit 9 is dialed with tone frequencies 852 Hz and 1477 Hz.

















Figure B-2. Standard DTMF frequencies Figure B-3. Extended DTMF frequencies

The extended DTMF characters (A, B, C, D) are the high-end frequencies (1633 Hz) defined on some
telephone sets with a fourth vertical column of buttons. This fourth column provides for extended PBX control
functions. The actual functions that are provided depend on the PBX manufacturer’s implementation and
feature set.







1 2 3

4

5 6 B

7 8 9

*



0 # D

1 2 3

4 5 6

7 8 9

* 0 #

A

C





93

Appendix C

Result Code Summary

Appendix

Multi-Tech Result Codes (

&Q0

)

Terse Verbose Definition

0OK
1 CONNECT
2 RING
3 NO CARRIER
4 ERROR
5 CONNECT 1200
6 NO DIALTONE

7 BUSY A busy signal has been detected.

8 NO ANSWER

9 CONNECT 2400
10
11 CONNECT 4800
12 CONNECT 9600
13 CONNECT 14400
19 CONNECT 19200
21 CONNECT 21600
23 CONNECT 1275

24 CONNECT 24000
26 CONNECT 26400
28 CONNECT 28800
31 CONNECT 31200
33 CONNECT 33600

Command was executed without error; ready for next command.
Modem has detected carrier and gone online.
Modem has detected ring caused by incoming call.
No carrier signal has been detected within the allowed time.
Error in command line (too many, or invalid characters).
Modem has detected carrier at 1200 bps and gone online.
No dial tone has been detected.

The remote system did not answer.
Modem has detected carrier at 2400 bps and gone online.
Not used.
Modem has detected carrier at 4800 bps and gone online.
Modem has detected carrier at 9600 bps and gone online.
Modem has detected carrier at 14400 bps and gone online.
Modem has detected carrier at 19200 bps and gone online.
Modem has detected carrier at 21600 bps and gone online.
Modem is connected in V.23 mode.

Modem has detected carrier at 24000 bps and gone online.
Modem has detected carrier at 26400 bps and gone online.
Modem has detected carrier at 28800 bps and gone online.
Modem has detected carrier at 31200 bps and gone online.
Modem has detected carrier at 33600 bps and gone online.

MNP Reliable Mode. If the modem connects using MNP error correction, the word
the

CONNECT

1R CONNECT RELIABLE
5R CONNECT 1200 RELIABLE
9R CONNECT 2400 RELIABLE

11R CONNECT 4800 RELIABLE
12R CONNECT 9600 RELIABLE
13R CONNECT 14400 RELIABLE
19R CONNECT 19200 RELIABLE
21R CONNECT 21600 RELIABLE
24R CONNECT 24000 RELIABLE
26R CONNECT 26400 RELIABLE
28R CONNECT 28800 RELIABLE
31R CONNECT 31200 RELIABLE
33R CONNECT 33600 RELIABLE

responses as follows:

RELIABLE

or the letter R is added to

94

Appendix

LAP-M Reliable Mode. If the modem connects using LAP-M error correction, the word

CONNECT

1L CONNECT LAPM
5L CONNECT 1200 LAPM
9L CONNECT 2400 LAPM

10 L CONNECT 4800 LAPM
12 L CONNECT 9600 LAPM
13 L CONNECT 14400 LAPM
19 L CONNECT 19200 LAPM
21 L CONNECT 21600 LAPM
24 L CONNECT 24000 LAPM
26 L CONNECT 26400 LAPM
28 L CONNECT 28800 LAPM
31 L CONNECT 31200 LAPM
33 L CONNECT 33600 LAPM

Data Compression. If the modem connects using data compression, the word
the

Standard AT Result Codes (

If standard AT command set responses are selected by the &Q command, the following result codes change:

9 Not used.
10

responses as follows:

CONNECT

responses.

CONNECT 2400

COMPRESSED

&Q1

)

Modem has detected carrier at 2400 bps and gone online.

LAPM

or letter L is added to the

or the letter C is added to

95

Appendix D

S-Register Summary

Register Unit Range Default Description

S0

S1
S2
S3
S4
S5
S6

S7

S8

S9

S10

S11

S13

S17

S24

S25

S30

S32

1 ring 0, 1–255 1 Sets the number of rings until the modem answers.

ATS0=0

1 ring 0–255 0 Counts the rings that have occurred.
decimal 0–127 43 (+) Sets ASCII code for the escape code character.
decimal 0–127 13 (^M) Sets ASCII code for the RETURN character.
decimal 0–127 10 (^J) Sets ASCII code for the LINE FEED character.
decimal 0–127 8 (^H) Sets ASCII code for the BACKSPACE character.
1 sec 2–255 2 Time the modem waits for a dial tone before aborting a call.

4–255† 4 †
4–7‡ 4‡

1 sec 1–255 45 Time the modem waits for a carrier signal before aborting a call.

1–45* 4 5*
1–55‡ 55‡

1 sec 0–255 2 Length of the pause by a comma character in a dialing command.

4–255† 4 †
4–7‡ 4‡

100 ms 1–255 6 Sets delay between when the modem detects a valid carrier

signal and when it turns on its CD circuit.

100 ms 1–254, 7 Sets how long a carrier signal must be lost before the modem

255 disconnects. S10=255 causes the modem to not disconnect with

loss of carrier.

1 ms 1–255 70 Sets spacing and duration of dialing tones. 50 ms is the

80-255* 80* recommended minimum.
80-255‡ 80‡

decimal 0, 1–127 37 (%) Sets ASCII code for remote configuration escape character.

S13=0 disables remote configuration.

10 ms 1–255 25 Sets the length of the break time (space) sent to the local PC

when the modem receives a remote break.

50 ms 0–255 20 Sets the time the DSR, CTS, and CD signals drop before going

high again. Used for some PBX and CBX phone systems.

100 ms 0, 1–255 0 Sets the time the DTR signal must be dropped before the modem

dis-connects. The 0 default equals 50 ms.

1 min. 0, 1–255 0 Sets how long the modem waits after the last character is

received or transmitted before it disconnects. The 0 default
disables the timer.

100 ms 0–255 20 Sets the time the modem will wait for a RETURN to be entered

during escape sequence execution.

disables auto answer completely.

Appendix

96

Appendix

S34

S36

S37
S43

S48

S94

1 char- 0–60 10 Sets the number of command characters allowed after +++AT.
acter

1 sec 0, 1-255 5 Sets the time between DTR inactive and modem off-hook.

S36=0 disables DTR busy-out.
1 sec 0-255 5 Sets the time between DTR active and modem on-hook.
decimal 33, 31, 0 Sets fixed V.34 connect speed.

28, 26, 28 = 28800 bps; 26 = 26400 bps;. . .
24, 21, 48 = 4800 bps. 0 default disables this feature.
19, 16,
14, 12,
96, or 48

decimal 33, 31, 0 Sets maximum V.34 connect speed.

28, 26, 33 = 33600 bps; 31 = 31200 bps;. . .
24, 21, 48 = 4800 bps. 0 default disables feature (same as S48=33).
19, 16,
14, 12,
96, or 48

1 sec 0–254, 4 5 Sets the maximum time the modem remains out of service when

255

*H1

is active. S94=255 causes the modem to remain out of
service indefinitely, until it receives an enable from the
management software.

97

Appendix E

AT Command Summary

Command Values Description

Appendix

AT

RETURN

A

A/

A:

&An

$An

#An

Bn n

n/a Attention Code

The attention code precedes all command lines except A/, A: and escape codes.

n/a RETURN Key

Press the RETURN (ENTER) key to execute most commands.

n/a Force Answer Mode

Answer call immediately without waiting for ring.

n/a Repeat Last Command

Do not precede this command with AT. Do not press RETURN to execute.

n/a Continuous Redial

Continuous redial of last number until answered. (10 redials in North American models.
Not used on International or U.K. models.)

n = 0 or 1 Answerback

*** &A0 Answerback off.

&A1 Answerback on.

n = 0 or 1 Auto-Reliable Buffering

*** $A0 Discard data received during establishment of reliable connection

$A1 Buffer data received during establishment of reliable connection

n = 0–3 Auto Speed Detection in Answer Mode

*** #A0 Start at maximum speed and fall back to 14400 to 12000 to 9600 to 4800 to

2400 to 1200 to 300 bps.
#A1 Maximum speed only.
#A2 Start at maximum speed and fall back incrementally to 4800 bps only.
#A3 Start at 2400 bps and fall back to 1200 to 300 bps only.

= 0 or 1 Answer Tone (International models only)

*** B0 Select ITU-T V.21 answer tone.

B1 Select Bell 103 answer tone.

&BSn n

$BAn n

&Cn n

= 0 or 1 Maximum Reliable Block Size

&BS0 Maximum transmit block size of 64 characters.

*** &BS1 Maximum transmit block size of 256 characters.

= 0 or 1 Baud Adjust

*** $BA0 Set baud adjust off, speed conversion on. (Serial port speed is independent of

modem data rate.)
$BA1 Set baud adjust on, speed conversion off. (Serial port speed is same as

modem data rate.)

= 0, 1, 2, Carrier Detect Control

or 4 &C0 Force Carrier Detect on.

*** &C1 Let Carrier Detect follow carrier signal.

&C2 Let Carrier Detect drop for time set by
&C4 Reset modem when Carrier Detect drops.

S24

on disconnect, then go high again.

98

Appendix

&CDn n

Ds s

DsNd s

&Dn n

%DCn n

%DFn n

%DPn n

>DTn n

= 0 or 1 Cleardown at Disconnect

= phone # Dial

= phone # Store Phone Number

d

= 0 or 1 To store, enter D followed by telephone number s, then N followed by directory

= 0, 1, 2, Data Terminal Ready Control

or 3 &D0 Modem ignores DTR signal.

= 0 or 1 Command Mode Control

= 0 or 1 Line Probe Data Format

= 0 or 1 Line Probe Data Read

= 0 or 1 DTMF Detection

*** &CD0 Enable cleardown.

&CD1 Disable cleardown.

Dial telephone number s, where s may include up to 60 digits or T, P, R, comma,
colon, and semicolon characters.

number d.

&D1 When DTR drops, the modem hangs up. While DTR is low, the modem accepts

*** &D2 Same as

*** %DC0 Enable command mode.

*** %DF0 V.34 line probe data displayed in graph format.

*** %DP0 Disable reading of line probe data during the V.34 handshake.

*** >DT0 Disable DTMF detection.

commands but will not dial or auto-answer until DTR goes high again.
&D3 When DTR drops, the modem hangs up and resets as if an

command was issued.

%DC1 Disable command mode.

%DF1 V.34 line probe data displayed in table format.

%DP1 Enable reading of line probe data during the V.34 handshake.

>DT1 Enable DTMF detection when off-hook.

&D1

.

ATZ

or an

AT&F

En n

= 0 or 1 Echo Command Mode Characters

E0 Do not echo command mode characters.

*** E1 Do echo command mode characters.

99

Appendix

&En n

$En n

= 0–15 V.42 Error Correction Modes

= 0 or 1 V.42 Error Correction at 300 bps

&E0 Non-error correction mode (V.42 disabled).

*** &E1 Auto-reliable mode.

&E2 Reliable mode (V.42 enabled).

Modem-Initiated Flow Control

&E3 Flow control disabled.

*** &E4 Hardware flow control.

&E5 XON/XOFF flow control.
XON/XOFF Pass-Through (

*** &E6 XON/XOFF not passed through.

&E7 XON/XOFF passed through.

Hewlett-Packard ENQ/ACK Pacing

*** &E8 ENQ/ACK pacing off.

&E9 ENQ/ACK pacing on.

Non-Error Correction Mode Flow Control

*** &E10 Non-error correction mode flow control off.

&E11 Non-error correction mode flow control on.

Pacing (Computer-Initiated Flow Control)

&E12 Pacing off.

*** &E13 Pacing on.

Data Compression

&E14 Data compression disabled.

*** &E15 Data compression enabled.

*** $E0 V.42 error correction at 300 bps disabled.

$E1 V.42 error correction at 300 bps enabled.

&E5

selected)

$EBn n

%En n

&Fn n

$Fn n

%Fn n

= 0 or 1 Asynchronous Word Length

= 0–5 Escape Sequence Options

= 0, 8, or 9 Load Default Configuration

= 0 or 1 Auto-Reliable Fallback Character Enable

= 0 or 1 Echo Canceler Offset Frequency Compensation

*** $EB0 10-bit mode enabled.

$EB1 11-bit mode enabled.

%E0 Modem won’t escape.

*** %E1 +++ method.

%E2 Break method.
%E3 Either +++ or break methods.

*** %E 4 No

%E5

&F0 Load factory default values from ROM.

*** &F 8 Read factory default values and DIP switch settings when &F is issued.

&F9 Read parameters stored in nonvolatile memory when &F is issued.

*** $ F0 Do not fall back to non-error correction mode connect if CR received.

$F1 Fall back to non-error correction mode connect if CR received.

*** % F0 Disable echo canceler offset frequency compensation.

%F 1 Enable echo canceler offset frequency compensation.

OK

response to +++.

OK

response to +++.

100