Black Box MD1276A User manual

MD1276A Global 56K/V90 Modem
User’s Guide
0049-2200-001 Rev.A
FEBRUARY 2004
0049-2200-500

Page ii
Contents
Introduction............................................................................................................................... 6
Installation................................................................................................................................. 7
Unpacking Your Hardware................................................................................................. 7
Additional Items You Need.................................................................................................. 7
Hardware Overview .......................................................................................................... 8
InstallationSummary........................................................................................................... 9
Connecting the Cables ..................................................................................................... 10
Driver Installation ...............................................................................................................11
ModemLED Display .......................................................................................................... 12
FrontPanelModeLEDs .................................................................................................... 13
TheATCommands............................................................................................................ 14
Selecting Speeds.............................................................................................................. 20
Flow Control..................................................................................................................... 24
Configuring the Modem..................................................................................................... 26
Error Correction...................................................................................................................... 27
Error Correction Protocols................................................................................................ 27
Security & Encryption ............................................................................................................. 32
Encryption ........................................................................................................................ 39
Synchronous Modes .............................................................................................................. 47
Leased Line Operations ................................................................................................... 51
DumbMode Operation ............................................................................................................ 54
The Option Switches........................................................................................................ 60
V.25bis Operations................................................................................................................. 61
DistinctiveRing ....................................................................................................................... 69
CallerID .................................................................................................................................. 70
CallLogging...................................................................................................................... 73
Commands.............................................................................................................................. 74
+++ Escape Sequence ..................................................................................................... 74
**** Remote Access Sequence ........................................................................................ 75
AT? Interactive CommandHelp ......................................................................................... 77
A/ RepeatLast Command................................................................................................. 78
ATA Answer ..................................................................................................................... 79
ATBn Select Communications Standard............................................................................ 80
ATDDial............................................................................................................................ 84
DialModifiers.................................................................................................................... 85
ATEEcho.......................................................................................................................... 90
ATHHangUp.................................................................................................................... 91
ATIIdentity........................................................................................................................ 92
ATLSpeaker Volume Control ............................................................................................ 93
ATMMonitor ..................................................................................................................... 94
ATO Return to On-line State ............................................................................................. 95
ATQ Quiet (Suppress Response Codes) ......................................................................... 97
ATRSetTerminalSpeed ................................................................................................... 98
ATSn? Display S Register Value..................................................................................... 100
ATSn= Set S Register Value........................................................................................... 101
ATV Verbal Response Codes ........................................................................................ 102
ATW Connection Speed Information ............................................................................... 103
ATX Extended Response Codes .................................................................................... 104

Page iii
ATZn Restore Configuration Profile................................................................................ 106
AT&B Character Length ................................................................................................. 107
AT&C Controlling Data Carrier Detect ............................................................................. 108
AT&DControlling Data TerminalReady ........................................................................... 109
AT&F.ReinitialiseModem .................................................................................................110
AT&F Restore Factory Defaults ...................................................................................... 111
AT&G Guard Tone ...........................................................................................................112
AT&HClock Control .........................................................................................................113
AT&K Flow Control ..........................................................................................................114
AT&L Leased Line ...........................................................................................................116
AT&M Synchronous/Asynchronous Mode ......................................................................117
AT&N Abort Connection................................................................................................... 119
AT&RRTS/CTS Control................................................................................................... 120
AT&SControlling DSR..................................................................................................... 121
AT&Vn View Active Configuration Profile ...................................................................... 122
AT&Wn Write Configuration Parameters......................................................................... 123
AT&XTransmit Clock ...................................................................................................... 124
AT&Yn Select Stored Profile on Power Up ..................................................................... 125
AT&Z Stored Phone Number ........................................................................................... 126
AT#A Universal Remote Access..................................................................................... 127
AT#B 1200bps Originate Mode....................................................................................... 129
AT#C V.25 Calling Tones ................................................................................................ 130
AT#CIDCallerID.............................................................................................................. 131
AT#D V.25bis Direct Calling ............................................................................................ 133
AT#E Encryption ............................................................................................................. 134
AT#HDisplay Help .......................................................................................................... 135
AT#I V.22bis Leased Line............................................................................................... 136
AT#J V.42 Capability Checking ....................................................................................... 137
AT#KMNP 10mode ........................................................................................................ 138
AT#MCommand ModeSelection..................................................................................... 139
AT#N V.25bis Character Encoding ................................................................................. 140
AT#O Buffer Overflow................................................................................................... 141
AT#Q V.25bis Terminal Speed ........................................................................................ 142
AT#REnableRemoteControl .......................................................................................... 143
AT#S Security Menu....................................................................................................... 144
AT#U V.25bis Character Set .......................................................................................... 145
AT#V Verifier ................................................................................................................. 146
AT%B AutoAnswer Setting............................................................................................ 147
AT%C Compression Control ........................................................................................... 148
AT%D Set Disconnect Delay .......................................................................................... 149
AT%EAuto EQM Retrain ................................................................................................. 150
AT%FDTR/DSR override................................................................................................ 151
AT%HMNP10 NegotiationSpeed ................................................................................... 152
AT%K CTS During Dial andHandshake .......................................................................... 153
AT%L Display Line Signal Level ..................................................................................... 154
AT%Ln Transmit Level (Data Mode) ............................................................................... 155
AT%MMode LEDIndication ............................................................................................ 156
AT%N Non-Standard Terminal Speeds............................................................................ 157
AT%PCONNECTMessageTiming .................................................................................. 158
AT%Q Line Signal Quality............................................................................................... 159
AT%R CTS Override....................................................................................................... 160
AT%S DSR Override ...................................................................................................... 161
AT%T DCD Override....................................................................................................... 162

Page iv
AT%U V.42 Response Codes ........................................................................................ 163
AT%W Welcome Message ............................................................................................. 164
AT\AMNPBlockSize ...................................................................................................... 165
AT\Bn Generate Break ................................................................................................... 166
AT\JAuto-Reliable Fallback ............................................................................................ 167
AT\K Break Control ......................................................................................................... 168
AT\N Asynchronous Operating Mode ............................................................................. 170
AT\Q Extended Flow Control .......................................................................................... 172
AT\S Display Active Configuration .................................................................................. 173
AT\Tn InactivityTimer (Data Mode) ................................................................................. 174
AT\V Error Correction Response Codes ........................................................................ 175
AT\XXON/XOFF PassThrough ...................................................................................... 176
AT*K Select Primary DES KEY from Stored Keys ........................................................... 177
AT*RV.13 Remote RTS Signalling................................................................................... 178
AT*S Change Current User Password ........................................................................... 179
AT*TAutoCallRedial ...................................................................................................... 180
AT*V Maximum V.42bis Dictionary Size.......................................................................... 181
AT*W Welcome Message Text ....................................................................................... 182
AT*Y Escape Seq. Detection in Sync. ............................................................................ 183
AT+ICF Character Framing and Parity Select .................................................................. 184
AT+MSSelectModulation ............................................................................................... 185
AT+MS=? Reporting Supports Options ........................................................................... 189
AT-Q MNP10 Fallback to V.22bis..................................................................................... 190
AT-DATETime & Date ..................................................................................................... 191
AT-LOGCall Log ............................................................................................................. 192
AT:E V.32 compromise Equaliser .................................................................................... 193
V.25BIS- CICConnectIncoming Call .............................................................................. 194
V.25BIS - CRNDial.......................................................................................................... 195
V.25BIS - CRS Dial Stored Number ................................................................................. 197
V.25BIS- DIC Disregard Incoming Call ............................................................................ 198
V.25BIS- PRNStored PhoneNumber ............................................................................. 199
V.25BIS - RST Reset ...................................................................................................... 200
S Registers........................................................................................................................... 201
ATS0 Rings Before Answer........................................................................................... 203
ATS1RingCount ............................................................................................................ 204
ATS2 Escape Sequence Character................................................................................ 205
ATS3 Carriage Return Character.................................................................................... 206
ATS4 Line Feed Character ............................................................................................. 207
ATS5 Backspace Character........................................................................................... 208
ATS6DialTone WaitTime ............................................................................................... 209
ATS7 Wait for Carrier ..................................................................................................... 210
ATS8 Pause Dial Modifier Delay.......................................................................................211
ATS9 Carrier Detect Response Time .............................................................................. 212
ATS10 Lost Carrier/Hang Up Delay ................................................................................ 213
ATS11DTMFToneTiming ............................................................................................... 214
ATS12 Escape Sequence Guard Time ........................................................................... 215
ATS16 Test in Progress (read only) ............................................................................... 216
ATS18 Test Timer ........................................................................................................... 217
ATS25 DTR Loss Detection ............................................................................................ 218
ATS26RTS/CTSDelay ................................................................................................... 219
ATS27 Delay Before Dial ................................................................................................ 220
ATS29 Hook Flash Duration............................................................................................ 221
ATS30 Inactivity Timer .................................................................................................... 222

Page v
ATS33 EQM Threshold Value ......................................................................................... 224
ATS38 Disconnect Delay................................................................................................ 225
ATS42 Modem Disconnect Reason ................................................................................ 226
ATS43 Break Sequence Length ..................................................................................... 227
ATS45 V.22bis EQM Threshold Value............................................................................. 228
ATS57DTR HighDetection ............................................................................................. 229
ATS62 V.42 Detection Timer........................................................................................... 230
ATS66 RemoteAccess Guard Time ............................................................................... 231
ATS67 Remote Access Character.................................................................................. 232
ATS69 Command LineTime-out ...................................................................................... 233
ATS71Ignore IncomingCall ............................................................................................ 234
ATS74 Disconnect Reason for Prev. Call ....................................................................... 235
ATS80 Flow Control High Water Mark ............................................................................ 236
ATS81 Flow Control Low Water Mark ............................................................................ 237
ATS82 Failsafe Flow Control Overrun............................................................................ 238
ATS95 Extended Response Codes ................................................................................ 239
ATS96Help Page Width.................................................................................................. 240
ATS97 Help Page Length................................................................................................ 241
ATS105 Voice ‘Dead Man’Timer ..................................................................................... 242
ATS122AutoRateChange............................................................................................... 243
ATS123AutoRateChange............................................................................................... 244
ATS124DurationEQM .................................................................................................... 245
Modem Response Codes...................................................................................................... 246
RS-232 Signals..................................................................................................................... 248
Abbreviated Command List................................................................................................... 251
Glossary............................................................................................................................... 261
Specifications ....................................................................................................................... 282
FCCRequirements forTelephone-LineEquipment ................................................................ 284

Page 6
Introduction
Welcome to the MD1276A Modem User Guide, a comprehensive guide to the efficient use of
your modem. Together with the Read Me First Guide supplied with your modem, this reference
manual provides all the information needed to make maximum use of your equipment and
software. This User Guide is divided into the following sections:
Getting Started
oA complete description about how to get started using your equipment, including basic
details and more advanced topics.
Error Correction
oExamines and explains the error correction features, includingV.42bis data
compression, of your equipment.
Security
oExamines and explains the data security and encryption features of your equipment.
Synchronous Modes
oFull details on how to use your modem for synchronous operations.
Dumb Mode
oProvides product specified information on Dumb Mode operation.
V.25bis Operations
oDescribes how your modem implements V.25bis and how it interacts with AT
commands.
Distinctive Ring
oExplains how to use Distinctive Ring and its associated commands.
Caller Id
oExplains how to use Caller Id and its associated commands.
AT Commands
oProvides a complete description of all commands available in your modem.
S Registers
oIntroduces you to S Registers and how to use them.
oContains a description of the available S Registers.
Response Codes
oThis section provides information on the response codes supported by your modem.
RS-232 Signals
oThis section provides information on signals supported on the modem’s RS- 232
socket.
Abbreviated Command Listing
oThis section provides a quick reference of the commands for the BLACK BOX®
MD1276A modem.
Glossary of Communications Terms
oProvides descriptions of modem, facsimile and other communications terms.

Installation
Page 7
Installation
Unpacking Your Hardware
Your package should include:
•The BLACK BOX®MD1276A modem
•An RJ-11 telephone-line cable
•A power supply module
•This User’s Guide
If your package contents are damaged or missing, please contact your place of
purchase immediately.
Additional Items You Need
To use your mode, you need the following additional items:
•Two- or four-wire transmission line or leased line
•A power source that provides 85 to 265 Volts AC, 50 to 60 Hz, single phase

Page 8
Telco/Dial Line
Telephone
Set DTE RS232
Connector Low Voltage
PowerInput
ON/OFF
Hardware Overview
Back View
The following figure shows the back view of the modem. Starting from the left side, this
view shows:
•A line jack for connecting the modem to the communications line.
•An audio jack for leased-line operation.
•Afemale, 25-pin RS-232 connector for connecting a standard DTE (RTU).
•A power connector.
•An ON/OFF switch.
Front View
The front viewof the modem has 10 LED status indicators. For more information about
these indicators, see “Modem LED Display”on page 14 and “Front Panel Mode LEDs”
on page 15.
LEDs (see page 15)
Option DIP Switch
(see page 62)
Data/Talk Switch
(see page 58)
Mode Switch for
Dumb Operation
(see page 56)

Installation
Page 9
Installation Summary
The modem installation involves the following steps:
1. Finding a suitable location for the modem. See the section below.
2. Making the necessary modem connections. See page 12.
3. Installingthe modemdriver. See page 13.
Findinga Suitable Location
The location you select for your modem should provide easy access to the back panel
communications interfaces and provide a clear view of the front panel LED indicators.

Page 10
Connecting the Cables
1. Turn off your computer.
2. Plug the data cable's male end (pins showing) into the connector marked RS232 at the back
of your Modem and then plug the female end (no pins showing) of the same cable into the
COM port at the back of your computer.
3. Your computer's COM port could be 9 pins or 25 pins. Use the appropriate connector on
the cable suppled to conntect your Modem to your Serial port.
4. Plug the telephone cable into the connector marked LINE at the back of your Modem and
the other end of the cable into your telephone wall socket.
+ Your Modem has a Telephone Set connector to allow 4-wire leased-line operation.
Refer to the section on Leased Line Operations for details on this feature.
5. Plug the power cable pin into the POWER connector at the back of your Modem and plug
the power supply into a suitable power point.
6. Use the ON/OFF switch to turn on your Modem. Then check that some of the Modem
lightsilluminate.
7. Restart your computer.
8. Now you need to install your Modem's Driver. Which operating system is your computer
running? Read the next section for driver installation instructions.
Telco/Dial Line
Telephone
Set DTE RS232
Connector Low Voltage
PowerInput
ON/OFF

Installation
Page 11
Windows 98
1. Please insert the driver CD supplied and, when the "Found New Hardware Wizard"
recognises the new Modem, click Next to search for the driver.
2. Select the "Search for the best driver your device. [Recommended]" and click "Next" to
continue.
3. Select the "Specify a location" option and type "D:\" where D:\ is the letter of your CD
ROM drive. Click "Next" to start the search for your driver.
4. Click "Next" to start the installation.
5. Click"Finish".
Windows 2000
Driver Installation
1. Windows will detect the modem automatically. Please insert the supplied CD and click
"Next".
2. Select "Search for a suitable driver for mydevice [recommended]", and then click "Next".
3. Select "Specify a location" and click "Next".
4. Enter the driver location "D:\" where D:\ is the letter of your CD ROM drive and click on
"OK".
5. Windows will find the correct driver for your modem. Click "Next" to continue.
6. When the "Digital Signature Not Found" screen appears, click "Yes" to continue.
7. Click "Finish" to end this procedure.
Windows ME
1. Please insert the supplied CD and, when the "Found New Hardware Wizard" recognises the
new Modem, select "Specify the location of the driver [Advanced]" and click "Next" to
search for the driver.
2. Select "Search for the best driver in these locations" and choose "Specify a location".
Type in "D:\" (where D:\ is the letter of your CD ROM drive) and click "Next" to continue.
3. Click "Next" to start the installation.
4. Click "Finish" to end this installation procedure.

Page 12
Modem LED Display
+ When your modem is using V.90, the Front Panel Mode LEDs will display the speed
closest to the K56flex speed.
Transmit Data (TXD)
LED will flash when the modem is sending data.
Receive Data (RXD)
LED will flash when the modem is transferring data from the remote to the local computer.
Off-Hook
LED will glow when the modem ison-line; ie. dialling or answering
Carrier Detect
LED will glow when the modem detects a valid carrier signal from a remote modem.
Auto-Answer
LED will glow to indicate auto-answering operation. If the modem is performing a test, the LED
will flash until the test is completed or cancelled.
Terminal Ready
LED indicates the ‘Data Terminal Ready’(DTR) signal is asserted.

Installation
Page 13
Front Panel Mode LEDs
Line Modulation One Two Three Four
K56flex 56000 bps ZMZMm m
K56flex 54000 bps ZMZMl m
K56flex 52000 bps ZMm m m
K56flex 50000 bps ZMl m m
K56flex 48000 bps ZMm l m
K56flex 46000 bps ZMl l m
K56flex 44000 bps m m m m
K56flex 42000 bps l m m m
K56flex 40000 bps m l m m
K56flex 38000 bps l l m m
K56flex 36000 bps ZMZMm m
K56flex 34000 bps l m l m
K56flex 32000 bps m l l m
K56flex 30000 bps l l l m
33600 bps ZFZFm l
31200 bps ZFZFl l
28800 bps ZFm m l
26400 bps ZFm l l
24000 bps ZFl l l
21600 bps ZMm m l
19200 bps ZMl m l
16800 bps ZMm l l
14400 bps l l l l
12000 bps l l m l
9600 bps m l m l
7200 bps m l l l
4800 bps l m m l
2400 bps ZSm m l
1200 bps ZS m l l
1200/75 bps ZSl m l
300 bps ZSl l l
Fax 14400 bps m ZSZSl
Fax 9600 bps m m ZSl
Fax 7200 bps m l ZSl
Fax 4800 bps l m ZSl
Fax 2400 bps l l ZSl
LED: l = Off m= On
Flashing:ZS = Slow, ZM = Med, ZF = Fast

Page 14
The AT Commands
The AT commands are a group of special commands recognised by your modem. These
commands derive their name from the letters AT, which are used to prefix commands. Before
continuing:
•Run your communications software and enter local mode (or terminal mode) at 38,400 bps
Refer to your communication software manual for details.
The Attention Code
An AT (sometimes known as the ATtention code) usually precedes all commands being sent to
the modem. It is used to gain the modem’s attention, informing it that you are about to send a
command. For example:
•Type the command: ATI9 <E>
Your modem’s firmware identity message will appear on your computer screen. If you type I9
only, your modem will not respond. If you type AT19, your modem will report an ERROR.
You may enter the attention code in all upper case, or all lower case letters, such as: AT or at
Multiple Commands
You may place multiple modem commands after an AT provided the total number of characters
does not exceed 80. For example, a valid command to display the modem’s firmware identity
twice is:
•Type in the command: ATI9I9 <E>
An AT is not required in front of the second I9 command. You only need one attention code for
each command line. To make this command more readable, you can add spaces between the two
commands:
•Type in the command: AT I9 I9 <E>
The modem will execute the command as if the spaces are not there.
The Escape Sequence
When you issue commands to the modem all dialogue is occurring between your computer and
the modem. This situation is known as local command state.
When you connect to a remote system, dialogue will be occurring between your computer and
the remote system. This is known as on-line state. Because the modem assumes, after it enters
on-line state, all the data you send it is to be sent on to the remote modem, it ignores any AT
commands you give it while in on-line state.
To force the modem to return to local command state, enter an escapesequence. An escape
sequence consists of a one second delay, three + characters typed rapidly and another one
second delay. For example:

ATCommands
Page 15
•Type: AT&T1 <E>
The modem will enter on-line state (this command actually causes the modem to enter test
mode, but is equivalent to entering on-line state).
Now try to view the modem’s firmware identity code:
•Type: ATI9 <E>
Your command will be ignored. This is because the modem assumes you are typing characters to
be sent to a remote system.
Now enter an escape sequence. Do not type any characters for one second, type +++ rapidly
and wait another full second. The modem will respond with an OK message to indicate it has
returned to local command state. You will be able to view the modem’s firmware identity.
Beforecontinuing:
•Type: AT&T0 <E>
This command is used to halt the test.
The Repeat Command
The repeat command is used to re-execute the last command issued to the modem. Issue the
ATI9 command and the modem’s firmware identity code will be displayed on the screen.
•Type: A/
The identity code will appear again.
You don’t have to enter AT before the repeat command. You also do not have to press the
ENTER key. This is the only modem command which does not require you to enter AT before
it, and one of the few commands which does not require you to press the ENTER key. The A/
command is intended primarily for re-dialling a telephone number that was previously engaged.
The Help Command
Your modem will display information about the AT commands it supports if you type a
question mark (?) in your AT command.
For example:
•Type: AT? <E>
Your modem will display a list of all the commands it supports.
•Type: AT?DTR <E>
Your modem will display a summary of commands involving DTR.
•Type: AT?\N3%C2&D2 <E>
Your modem will display summaries of the \N, %C and &D commands.

Page 16
Response Codes
Your modem is capable of telling you, with on screen messages, what it is doing. These messages
are known response codes or result codes, and you will see them from time to time.
For example:
After a command is successfully executed, the response is: OK After a connection is established,
the response is: CONNECT A complete list of Response Codes can be found in Appendix A.
Dialling
TheAT commands may be used to initiate dialling with the modem.Your modem does not
require a telephone handset to be connected to it in order to dial.
The D (Dial) command is used to initiate a telephone call. The most basic form of the D
command is:
ATD number where the number is the telephone number you are dialling.
Having set your communications software for 38,400 bps operation:
•Type: ATD01234 <E>
Your modemwill begin to dial.
+ If your modem receives a character from your computer while dialling is being
performed, it will immediately hang up, send a NO CARRIER response message to
the computer and return to local command state. After a few seconds the message
CONNECT will appear on the screen.
If a NO CARRIER message appears, then your modem has not been able to make a connection.
Check your communications software is set for 38,400 bps operation and your modem is
correctly connected to your computer and the telephone line. You may use theA/ command to
redial.
To hang up the modem, enter an escape sequence (+++). The modem will respond with an OK
message.
•Type: ATH <E>
The modem will hang up.
+ Your computer must assert the DTR signal before dialling can start. Usually, this
is done by your communications software. If the DTR signal is lowered at any
stage of communications, after the &D2 command has been issued, the modem
will hang up and return to local command state. Interpretation of the DTR signal
may be changed with the &D command.

ATCommands
Page 17
Dial Modifiers
Dial modifiers are characters than can be included in a phone number to make the modem
perform specialtasks while dialling. For example, not all modem users will be using a dedicated
telephone line. Some users will have their modems connected to PABXs. To allow users of
PABXs to operate their modems successfully, dial modifiers are supported on the modem.
Most PABXs require you to dial 0 or 9 (in order to obtain an outside line) and wait for a dial
tone before dialling the actual phone number. Using dial modifiers, you can successfully dial the
phone number 12345 through a PABX using the command:
ATD0,12345
The , (comma) dial modifier causes the modem to pause for a short time after dialling 0. This
allows most PABXs sufficient time to obtain a line before dialling.
The factory default delay for the , modifier is two seconds. You may change the length of this
delay if necessary. Its length is determined by the value in S Register 8.
Another method of making the modem wait for a dial tone is to include the W dial modifier. The
W modifier causes the modem to examine the phone line to ensure a dial tone has been applied
before dialling starts:
ATD0W12345
If the modem cannot detect a dial tone within the time specified by S Register 7, the modem will
return to local command state and send a NO DIALTONE message to the computer (if either the
X2, X4, or X5 commands have been issued).
Due to differences with some older telephone exchanges, dial tone detection may not be possible
with your modem. Your modem will only recognise dial tones between 200 Hz and 600 Hz.
If your telephone line supports tone dialling then a useful dial modifier is the T modifier.
Inserting a T modifier before the number you are dialling causes the modem to tone dial that
number. For example:
ATDT12345
This will cause the modem to dial the phone number 12345.
These modifiers may be placed at any point in the number you are dialling and they may be
intermingled in the same number. More information about dial modifiers can be found in the
Command Descriptions chapter of this guide.

Page 18
Hanging Up
The H command is used to hang up the modem. After you have finished communicating with
another computer you must hang up your modem. Similarly, you must hang up the phone after
calling another person. If you don’t, no one will be able to call you and you may even be charged
for the length of time the phone was off the hook.
To hang up your modem:
•Type: ATH <E>
The modem will return an OK response message.
Stored Number Dialling
Your modem has the ability to store phone numbers which may be dialed at a later time. This is
similar to ‘abbreviated dialling’, which may be supported by your telephone.
To store a phone number use the &Z command. For example:
•Type: AT&Z1=012345 <E>
The phone number 012345 will be stored as phone number one. The S dial modifier is used to
dial a phone number that has been stored in your modem:
•Type: ATDS=1 <E>
The modem will dial stored phone number one.
+ Do not include an AT, D command, or S dial modifier in the stored phone number.
If synchronous mode 2 is being used, the ; (semi-colon) dial modifier should not
be included.
Answering Calls
As well as dialling other modems, your modem can answer calls made to it by other modems.

ATCommands
Page 19
Your modem is pre-configured to automatically answer any incoming call, provided it is
switched on, is in local command state, DTR is high and is not performing a test. If you receive a
call on the phone line the modem is connected to, it will answer the call and attempt to connect
to the calling modem.
S Register 0 contains the number of rings the modem will wait before answering a call. If a value
of 4 is placed in S Register 0, the modem will answer an incoming call immediately after the
fourth ring. If a 0 value is placed in S Register 0, the modemwill not answer an incoming call.
The communications standard used by the modem in its attempt to connect with a calling
modem is determined by the B command.
If the phone does ring, and verbal response codes are selected (ATV1), the modem will issue
RING messages until the number of rings stored in S Register 0 is reached. The modem will then
go on line, transmit an answer tone, and attempt to connect to the calling modem using the
communications standard selected by the B command.
By default the modem is set to B0. B0 is the auto range setting. This should connect to virtually
all communications standards and normally you do not have to alter this. As soon as a
connection is established, the modem will send a CONNECT message to your computer and
enter on-line state in answer mode.

Page 20
Selecting Speeds
The following section describes how to select line and terminal speeds for your modem.
Terminal Speeds
Your modem has the ability to communicate with your computer at various speeds. The modem
offers two speed modes: variable speed mode and constant speed mode.
Constant speed mode forces your modem to maintain the terminal speed that was selected when
you dialed another modem, even if the connection speed made with the other modem does not
match the terminal speed of your modem and computer.
For example, if your modem connected to another modem at 2400 bps and its terminal speed is
9600 bps, the modem will maintain its terminal speed at 9600 bps. Because of this, you must
select flow control between the modem and your computer. To select constant speed mode:
•Type: AT\N0 <E>
For more details on constant speed mode and flow controls, see the Command Descriptions
chapter for a discussion of the \N, B and &K commands. + Some computers cannot cope with
receiving data at speeds above 19,200 bps. If you wish to run at high speeds, you should install
a COM port that has a 16550 chip in place of your regular COM port. The 16550 chip allows
your computer to accept data at very high speeds when used with suitable drivers and software.
Variable speed mode allows your modem to automatically adjust its terminal speed to match the
line speed. For example, if your modem connects to another modem at 4800 bps and its terminal
speed is 9600 bps, the modem will automatically change its terminal speed to 4800 bps (and,
thus, you or your software would have to change the speed of your computer to 4800 bps).
If you have variable speed mode and B0, B1, B2 or B9 selected, the modem will attempt to
connect at a speed to match the terminal speed.
At 300 bps, select B0 or B2 for V.21, or B1 for Bell 103. At 1200 bps, select B0 for V.23, B1 for
Bell 212A, or B2 for V.22.
Variable speed mode may be selected by:
•Type: AT\N1 <E>
For more details about the variable speed mode, see the \N and B commands in the Command
Descriptions chapter of this guide.