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The Intelligent Choice in Data Communications



Sportster High Speed Modems
with V.42 bis

Manual Revision Date: 4/1/94

Copyright 1994 by U.S. Robotics, Inc.
8100 North McCormick Blvd.
Skokie, Illinois 60076-2999
All Rights Reserved


Factory Configuration (&Fn and Yn)
Permanent Configuration Templates (&Fn)
Programmable Templates (Yn)
Customizing Your Defaults (&Wn)
Using AT Commands
Resetting the Modem (Z)

Dial (D)
Cancel Dialing
Dial Command Options
Dial Type-Pulse or Tone
Adaptive Dialing (X2-X4)
Wait for Another Dial Tone (W)
Pause (,)
Slash (/)
Dial and Return to Command Mode (;)
Dialing Letters (")
Transferring Calls (!)
Wait for an Answer (@)
Reversing Originate/Answer Frequencies (R)
Dialing Stored Numbers (DSn)
Dial the Last Dialed Number (DL)
Re-execute the Last Command (A/)
Suppressing Auto Answer
Manual Answer
Points to Remember
Disconnecting and Hanging Up
Escape Code Operations (+++)
Modem Response to +++
Returning Online (On)
Hanging Up (Hn)
Break Handling (&Yn)
International Calls
ITU-T/Bell Answer Sequence (Bn)
Guard Tone (&Gn)
Pulse Dial Make/Break Ratio (&Pn)
ITU-T V.21-300 bps
ITU-T V.23-1200/75 bps

Tone Dialing
Volume Control (Ln)
Speaker Control (Mn)
Local Echo
Command Mode Local Echo (En)
Online Local Echo (Fn)
Result Codes
Response Modes (Vn)
Quiet Mode (Qn)
Result Code Options (Xn)
Additional Result Code Options (&An)
Error Control (&Mn)
Auto Answer with Error Control
Data Compression (&Kn)
Data Rate Commands
Software Requirements
Serial Port Rate (&Bn)
Connection Rate (&Nn)
Flow Control
Warning on Software Flow Control
Software Flow Control Precautions
Transmit Data Flow Control (&Hn)
When it is Required
Received Data Flow Control
Hardware Control (&Rn)
Software Control (&In)
Serial Operations
Carrier Detect (&Cn)
Data Terminal Ready (&Dn)
Data Set Ready (&Sn)

Inquiries (In)
S-Register Query (Sr?)
Stored Phone Number Query (&Zn?)
Last-Dialed Number Query (DL?)
Help Screens
Stop/Restart Display
Cancel Display
Basic Command Set ($)
Ampersand Command Set (&$)
Dialing (D$)
S-Register Functions (S$)

Testing with &T
Dial Test-S16=2

Fax Operations
Voice/Data Communications

The Serial Interface
Default Settings

How Modems Work
Modem Configuration
Line Travel
Digital Data
Flow Control
Error Control
ITU-T V.42 Handshaking
MNP Handshaking
Data Compression
Flow Control
Online Fallback/Fall Forward
Throughput Guidelines
Achievable Throughput Statistics


The Sportster is preconfigured at the factory so you should
be able to connect the modem, set up your communications
software, and be ready to send and receive data. Many users
won't need to change the default configurations, but if you
want to, this guide will tell you how. Many of the
functions described below can be handled by your
communications software, but you also have the power to
place your computer in Terminal mode (via your
communications software) and control the modem directly.

NOTE: Unless otherwise indicated, settings listed as
"default" are based on those set for the modem when it is


The Sportster is preconfigured at the factory with three
permanent and two programmable templates.

Permanent Configuration Templates (&Fn)

The following permanent templates come with your Sportster.
The default template consists of the most reliable settings,
but these settings may not work for all users.

&F0 This template does not include performance features,
such as a fixed serial port rate or hardware flow
control. What it does offer is compatibility with
non-typical computers or software that cannot handle
flow control and other features.

&F1 Default. This template sets the modem to
hardware flow control, a fixed serial port rate, the
highest level result codes, and the most complete
result-code set.

The &F1--Hardware Flow Control template is
recommended for all IBM-compatible computers, as long
as your communications software supports hardware
flow control, a fixed serial port rate, and the
advanced result-code subset.

NOTE: We also recommend that users of Macintosh
computers invest in a Hardware Handshaking cable
(instead of the standard cable), use this template,
and use software that supports hardware flow control.

&F2 This is a software flow control template. We
recommend you do not use software flow control, and
thus, this template. However, if you use a
Macintosh, see the note above. In addition, some
computers are limited to three-wire cables that do
not support hardware flow control signals. If this
is the case, review the warning on software flow
control later in this guide.

To load the &F2--Software Flow Control template and
save it as your power-on/reset default, enter the
following command:


NOTE: Refer to the "Programmable Templates" section
for more information on selecting and modifying
templates to save as your start-up configuration.

If you need a low performance template because of data-
transfer difficulties, flip DIP switch 7 ON and reset the
modem (ATZ command), or load the &F0--Low Performance
template by entering the following command:


NOTE: When the modem receives the above command, it assumes
you want to load the &F0 template because there is no
position number indicated. It is the same to enter AT&F as
to enter AT&F0.

This template allows you to communicate with non-typical
systems that cannot handle flow control and other features.

Programmable Templates (Yn)

In addition to the &Fn permanent configuration templates,
two programmable templates are provided. Your programmable
templates are located in nonvolatile, random access memory

The Sportster is shipped to load NVRAM template 0 (or Y0)
for its power-on/reset default settings.

Possible NVRAM templates:

Y0 Loads the NVRAM template 0 (stored with template
&F1--Hardware Flow Control settings). Default.

Y1 Loads the NVRAM template 1 (stored with template
&F2--Software Flow Control settings).

If you want to switch the power-on/reset default NVRAM
template from Y0 to Y1, enter the Yn command, then reset the
modem with the Z command.


To customize other defaults you want to store in NVRAM as
part of your customized power-on/reset template, use the &Wn
command (below).

WARNING: The Yn command, which selects template settings to
use as the power-on/reset default, may select different power-
on/reset default settings than those currently loaded (if you
altered the settings during the current session). Before
changing a template, you may want to use option 4 of the
Inquiry (I) command to display the current settings.
current settings.


The Y setting on the ATI4 screen indicates if Y0 or Y1 is the
power-on/reset default. If you want to check all the NVRAM
settings in both Y0 and Y1 templates, use option 5 of the
Inquiry command (I).



When the modem is shipped, it reads template 0 in NVRAM as
the power-on/reset default. Template 0 (Y0) is initially
loaded with &F1 permanent configuration settings. Although
you cannot alter the &F1 template, you can add, delete, or
modify the settings stored in your NVRAM templates. It is
more likely, however, that you will want to keep your power-
on/reset default settings and simply change a setting for a
current session. Refer to "Temporarily Changing a Setting"
in this guide for more information.

If you want to modify your default configuration settings,
use the &Wn command. Possible settings are:

&W0 Modifies the NVRAM 0 template (Y0).

&W1 Modifies the NVRAM 1 template (Y1).

Typically, users prefer the default settings stored in NVRAM
when the modem is shipped, but you may set up different
power-on/reset defaults. For instance, if your system
supports hardware flow control, you can set your Y1 template
to the settings for hardware flow control so both templates
set the modem for hardware flow control. (The Y0 template
is shipped with hardware flow control settings.)

AT &F1 &W1

NOTE: Yn is unique because it writes itself to NVRAM-you do
not need to use the &Wn command.

Similarly, if your system only supports software flow
control, you can set your Y0 template to the settings for
software flow control so both templates set the modem for
software flow control. (The Y1 template is shipped with
software flow control settings.)

AT &F2 &W

You may also specify the entire configuration in a single
command string that ends with the &Wn command. The
following example sets the modem for the current session and
stores the configuration in NVRAM 1 (or Y1).

AT &K3 &W1

After sending a configuration to NVRAM, you can change any
setting just for the current session, as in the following
example. The NVRAM configuration remains intact.

AT &K3

But if you want the new setting to be a default, write it to
NVRAM at the same time, as in the following example, which
saves the setting to NVRAM template 0.

AT &K3 &W

If you've sent the modem commands to change settings
throughout your session and want to save your current
configuration, send just the &Wn command. The current
settings are then written to NVRAM 0 (or Y0) in the example


If you cannot use hardware flow control and need to use
Xmodem-type file transfer protocols, use either Y0 or Y1 for
a no flow control configuration with no error control.

AT &F &M &W
AT &F &M &W1


To send commands directly to your modem, first put your
computer in Terminal mode. Some communications programs do
this automatically upon loading. Others require you to
display a communications terminal screen, press a Function
key, or perform some other operation. If necessary, refer
to your communications software documentation for

1. Type all commands in either upper case (AT) or lower
case (at), but not a combination (At).

2. All commands except A/ (re-execute last command) and
+++ (escape code) are preceded by the AT prefix and are
executed with the Enter/Carriage Return key ().

3. Command string length = 40 characters, maximum. The
modem doesn't count the AT prefix, Carriage Return
character, or spaces. In a dial string, it counts--but
doesn't act on--punctuation such as hyphens and

4. A missing numeric parameter is assumed to be zero, as
in the command to hang up; ATH is the same as
ATH0 .


If you've changed several current settings and want to reset
to your power-on defaults, type the following command.


The modem reads its DIP switch settings and resets to its
NVRAM defaults (DIP switch 7 OFF) or the &F0--Low
Performance template (DIP switch 7 ON) settings.

NOTE: Use the ATZ command if you've changed the position of
DIP switches 1-7 while the modem is on, so that the modem
can read the new settings. The only other way to initiate a
new setting for switches 1-7 is to turn the modem off and on


NOTE: Unless otherwise indicated, settings listed as
"default" are based on the hardware flow control template
stored in NVRAM when the modem is shipped.


To dial a phone number and place a call without using your
software's dialing directory, first put the computer in
Terminal mode. Then type the AT and D commands, the number
you wish to connect with, and press Enter. Spaces in our
command examples are ignored by the modem and are only
included for readability.

ATD 1234567

Unless you lowered your modem's speaker volume, you will
hear the modem go off hook and dial the telephone number,
followed by a series of handshaking signals.

The Dial command string may include up to 40 characters.
The modem counts but ignores punctuation characters such as
parentheses and hyphens. It does not count spaces, the AT
prefix, or the Carriage Return key () required to
execute the command.

The modem also executes any other commands or options
included in the command line. The following Dial command
example instructs the modem to turn off the speaker (M0),
and dial (D) the phone number (1234567) using tone dialing

AT M0 DT 1234567

You may want to review the many options on the next several
pages that are available for tailoring Dial strings. The
most typically used are the Dial Type--Pulse or Tone, and
the Pause options--comma, slash, and W.

Cancel Dialing

To cancel Dial command execution, press . If you
inadvertently hit a key on the keyboard while the modem is
dialing, the call is canceled. If this occurs, type the A/
command, which re-executes the last command you entered.

Dial Command Options

You can modify the dial string according to the needs of the
connection. Listed below are options available to you when
entering the Dial string.

Dial Type-Pulse or Tone
The modem defaults to pulse (rotary) dialing. To have the
modem use tone dialing, which includes the asterisk (*) and
pound sign (#), use the T command.

Dial type commands may be included in the Dial string (ATDT
number) or, issued separately (ATT or ATP). However, if
you'll always use tone dialing, write tone dialing to NVRAM
as the modem's default and/or use adaptive dialing,
described below.

NOTE: You can switch from one dial type to another within a
dialing sequence. The modem remains set to the last dialing
type instruction until it is reset (ATZ command), or it
receives a different dial-type command.

Adaptive Dialing (X2 through X4)
When any of the X2 through X4 (default) result code options
is in effect and you do not issue a dial type in the Dial
string, the Sportster defaults to pulse dialing. If you
issue a tone dial command, the Sportster will default to
Hunt dialing, beginning with tone and adapting to pulse when
necessary. For instance, if the phone company's central
office does not have tone-detection equipment, the modem
automatically reverts to pulse dialing.

Wait for Another Dial Tone (W)
This command is useful in situations where you must wait for
a second dial tone before continuing to dial. For example,
if you need to dial for an outside line, as in the following
example, the Sportster continues to dial as soon as it
detects the next dial tone.


NOTE: This command executes only if result code option X3
or X4 (default) has been issued. If the modem is set to X2
or lower, the modem interprets the W as a comma (two-second

Pause (,)
A comma causes a two-second delay in the dial sequence. The
following example contains four-second delays at several

ATDP 9,,7654321,,55555,,1 312 1234567

The first four-second pause is to access an outside line
after dialing 9, but you may wish to use the W option, just
described. The second pause is to make sure the remote
system is ready for the user's account number, and the
third, to delay before dialing the long-distance number.

Such pauses, however, may not be necessary. Experiment and
use delays only as required.

Slash (/)
A slash (/) can be used in any command string to make the
modem pause for only 125 milliseconds. Some users find it
helpful to have the shorter delay of a series of slashes,
rather than the 2-second comma pause.

Dial and Return to Command Mode (;)
If your phone is plugged into the modem, you can use this
option to have the modem Auto Dial a telephone rather than a
modem. The Sportster dials, remains off hook, and returns
the OK message, indicating it is in Command mode.

For example, to have the modem place a voice call, enter the
Dial command with a semicolon.


When the modem returns the OK result, pick up your phone
receiver so you can talk to the other party, and send the
command that hangs up the modem.


Similarly, if you can call a recorded weather or other
service, have the modem Dial, listen to the recording over
the modem's speaker and, when you are finished, instruct the
modem to hang up.

Dialing Letters (")
Quotation marks are used to make the modem dial
abbreviations and acronyms used as phone numbers, such as
DIAL USR (the U.S. Robotics Sales Department's 800 number).
This option is called Quote mode. Quotation marks are
inserted at the beginning of the alphabetic string.


NOTE: If you are including another command after the dial
string, use closing quotation marks before the additional

ATDT "DIAL USR",,,1234

Transferring Calls (!)
This command is used for modems installed where other modems
share the phone line. The modem flashes the switch-hook.
That is, it goes off hook 0.5 seconds, on hook for 0.5
seconds, and off hook again to dial the specified extension.
The following example includes instructions to return to
Command mode (;) and to hang up (H).

ATDT !1234;H

Wait for an Answer (@)
Some online services answer the phone and return a tape-
recorded request for information before processing
transactions. In such instances, the @ command can be used
in the Dial string to tell the modem to detect at least one
ring, wait for five seconds of silence at the other end of
the call, and then continue to execute the Dial string.

To use the @ command, set the modem result code option to X3
or X4 (default). If the modem is set to X2 or lower, the
modem returns an ERROR message when encountering the @
character in a command string.

In the next example, the modem is set to the X3 result code
option and dials a banking service. Each occurrence of @ in
the example indicates a five-second wait for silence. That
is, for taped requests from the bank for a password (12345),
an account number (6789), and a transaction code (2). The
transaction code might indicate, for example, a request for
an account balance.

ATX3 DT5551234 @ 12345 @ 6789 @ 2

If the necessary conditions do not occur--no rings, or no
following five seconds of silence--the modem times out as it
normally would (after 60 seconds). It then sends the
message NO ANSWER to the screen and aborts the call.

Reversing Originate/Answer Frequencies (R)
This command allows calls to an originate-only modem (a
modem set up to send only). It reverses the modem's
originate/answer frequencies, forcing the Sportster to dial
out at the answer frequency. The command follows the Dial
command, before or after the phone number.

AT D1234567R
AT DR1234567

Dialing Stored Numbers (DSn)

You can store up to four frequently used telephone numbers
in nonvolatile, random-access memory (NVRAM). Use the &Zn=s
command to store telephone numbers, where n is the position
of the number in NVRAM (0-3) and s is the stored number.
The following command string stores the telephone number
(4441212) at position 1 in NVRAM.


To dial a stored number, use the DSn command, where n is the
position of the number in NVRAM (0*3). In the first
example, the modem dials the phone number stored at position
0. In the second, the modem dials the phone number stored
at position 3.


You can also store a partial dial sequence. If you often
call a set of phone numbers and only their last three or
four digits differ, it might be useful to store the other
digits. The following example stores a partial phone number
at position 1.

AT&Z1 = 9W1 616 123

Once you have stored the partial phone number in NVRAM, use
the DSn command to dial the partial number, placing a slash
(/), then the remainder of the number after the DSn command.
The slash separates the DSn number from the remainder of the
string, yet maintains the dial command..

AT DS1/4567

NOTE: Do not include modem settings in the &Zn=s string.
If the call requires modem settings, insert them in the
command string before the DSn command. For example, &K3
(selective data compression) is inserted before the Dial
command to call the number stored at position 0.


This establishes &K3 as the current setting. To return to
default data compression mode after the call, issue the
following command.



The most frequent reason for redialing is receipt of a busy
signal. The Sportster modem provides two redialing options,
as follows.

Dial the Last-Dialed Number (DL)

When you want to redial a number, enter the DL command. The
modem dials the last-dialed number, which it has stored in a
special buffer.


To display the number stored in the last-dialed buffer, use
the following query.


To write the last number dialed to NVRAM, use &Zn=L where n
is the position in NVRAM. The following example stores the
last-dialed number at position 3.


If a number is already stored at position 3, that number is
overwritten with the last-dialed number.

Re-execute the Last Command (A/)

Another option for redialing is to enter the A/ command.
This command does not require the AT prefix or a Carriage


When the modem receives a command, it stores it in its
command buffer until it receives the next AT command. Note
that if you've sent the modem an additional command since
the Dial command, A/ repeats that command instead of


Your Sportster modem is shipped with DIP switch 5 ON, Auto
Answer suppressed. To set the modem to automatically answer
incoming calls, do one of the following.

Before powering on the modem...
* Set DIP switch 5 OFF. When you power on, the modem
answers incoming calls on the first ring.

If you want the modem to answer after several rings, set
DIP switch 7 OFF. Specify the ring you want the modem to
answer on in NVRAM (default=1 ring). The valid range is
1-255 rings. Power off the modem and power it on again
with its new DIP switch and NVRAM settings..

During a current session...
* Issue the following command to have the modem answer on
the fourth ring:


When the modem senses a call, it sends the RING result code
to your screen, goes off hook, and sends the remote modem a
high-pitched answer tone. If there is no Carrier Detect
within 60 seconds, the modem hangs up. If the connection is
made, the modem returns a CONNECT result code. When the
call is disconnected by you or the remote user, the modem
hangs up and returns the NO CARRIER code.

Suppressing Auto Answer

To disable Auto Answer, set DIP switch 5 ON before powering
on the modem, or set the modem to answer on zero (or no)
rings during the current session.


NOTE: The S-Register setting S0=0 cannot be saved to NVRAM.

Manual Answer
If you've disabled Auto Answer but are expecting an incoming
data call, use the Manual Answer command. Send the modem
the following command after the RING result code appears on
your screen.


When the call is disconnected, the modem returns to its
original state, Auto Answer disabled.

Points to Remember
1. You can set the modem to receive calls when you're not
at your computer. Load your communications software as
you normally do, and set the modem to Auto Answer. Also
set your software's file-save function to save incoming
messages and/or files.

2. If you've attached your phone so it can be used for
conventional calls, disable Auto Answer when you are not
expecting incoming data calls. Otherwise, your modem
may answer the phone before you do, greeting a voice
caller with a high-pitched, irritating answer tone.


The commands outlined below describe how you can instruct
the modem to disconnect the call and hang up the line.

Escape Code Operations (+++)

Once the modem is online to another system, the only command
it recognizes is an escape code of three plus symbols that
forces the modem into Online-Command mode. Issue the
escape command in the following sequence.

* Wait one second after sending the last item of data.
* Type three plus symbols (+++).
* Wait one second before typing any data.

Do not type the AT prefix or a Carriage Return. The guard
time of one second before and after prevents the modem from
misinterpreting the presence of the +++ symbols in the
transmitted data stream.

If necessary, the character used in the escape code or the
duration of the guard time can be changed by resetting
Register S2 or S12. See the "Quick Installation Guide" for
more information.

Modem Response to +++
When the modem receives +++, by default it enters Online-
Command mode and returns the OK result code. It maintains
the connection and is ready to act on commands. You may
then choose one of the following options.

* Issue commands to the modem and then return it online.
* Hang up the modem.

Alternatively, if you want the modem automatically to hang
up on receiving the +++ escape code, set Register S14 to 1
and write the command to your NVRAM templates.

ATS14=1 &W &W1

The modem disconnects and sends the NO CARRIER result code
to the screen.

Returning Online (On)

After forcing the modem into Online-Command mode with the
escape code sequence, you can issue commands and then toggle
the modem back online with the O command, as in the
following example.


O0 Return online (normal).

O1 Return online and retrain. If errors occur during a
non-ARQ connection, try this option. The modem returns
online and requests that both modems resynchronize.

Hanging Up (Hn)

At its default setting, the escape code forces the modem
into Online-Command mode but leaves the line open. To hang
up the modem, issue the following command once the modem
sends the OK result code.


H0 Hang up (go on hook).

H1 Go off hook.

Break Handling (&Yn)

This command lets you send a Break to abort data transfer
without disconnecting from the phone line interface.

&Y0 Destructive, no Break transmitted: the modem clears
the data from its transmit buffer (all data is lost)
but does not transmit the Break to the remote modem.

&Y1 Destructive, expedited: the modem clears the buffer
and immediately sends a Break to the remote modem.

&Y2 Nondestructive, expedited: the modem retains data in
the transmit buffer, but immediately sends a Break to
the remote modem.

&Y3 Nondestructive, unexpedited (send Break in sequence):
the modem transmits any buffer data received before the
Break, sends the Break, and then sends any subsequent
input from the computer.

NOTE: If the call is under MNP5 data compression,
destructive Breaks cause both modems to reset their data
compression tables. When transmission resumes, the modems
build new tables, and the result is lower than normal


The following commands apply to international calls.

ITU-T/Bell Answer Sequence (Bn)

To answer international calls, use the default B0 setting.

B0 Default. This setting is required for V.32 or higher
modems to answer V.32 or higher calls. It also selects
the ITU-T V.25 answer sequence, used outside of North

B1 This setting selects the Bell 2225 Hz answer tone used
in the U.S. and Canada and may be used when the remote
modem operates at only 2400 bps or lower. However, if
the modem is set to B1, it won't be recognized by V.32
or higher modems and can't answer calls at 9600 and

Guard Tone (&Gn)

The United Kingdom and some Commonwealth countries use phone
switching systems that require answering modems to send an
1800 Hz guard tone after they send an answer tone. Some
other European phone networks require a 550 Hz guard tone.
Guard tones are not used in the United States or Canada.

&G0 No guard tone, U.S./Canada. Default.

&G1 550 Hz guard tone follows answer tone. Requires B0

&G2 1800 Hz guard tone follows answer tone, United Kingdom
and some Commonwealth countries. Requires B0 setting.

Pulse Dial Make/Break Ratio (&Pn)

This command sets the ratio of the off-hook/on-hook
(make/break) interval for pulse dialing. The default sets
the modem for use in North America. The ratio must be
changed if the modem is used to dial out in the United
Kingdom and some Commonwealth countries.

&P0 Make/break ratio, U.S./Canada: 39%/61%. Default.

&P1 Make/break ratio, United Kingdom, some Commonwealth
countries: 33%/67%.

ITU-T V.21-300 bps

Select this option to call or answer overseas modems at 300
bps. In V.21 mode, the modem answers Bell 103/V.21 calls,
but only originates V.21 calls. This option is enabled in
Register S27 with the following command.


ITU-T V.23-1200/75 bps

Some United Kingdom and European systems require a 1200-bps
speed with a 75-bps back channel. This option is enabled in
Register S34 with the following command.



When you change a setting, the modem retains it until you do
one of the following.

* Change the setting again.
* Issue the ATZ command to reset the modem.
* Turn the modem off and power it on again.

The parameters described in this section are organized in
the order of their likely use. That is, those you are most
likely to use appear at the beginning of the section, and
those you are least likely to use appear toward the end.


The modem defaults to pulse (rotary) dialing. To have the
modem use tone dialing, which includes the asterisk (*) and
pound sign (#), use the T command.

ATDT 4445555

To have the modem always use tone dialing, use the T and &W

AT T &W &W1


The modem's speaker enables you to monitor the dial-connect
process. There are several ways to make use of this
feature. After the Sportster modem dials a number, it waits
up to 60 seconds for a high-pitched answer tone from the
other modem, immediately followed by data signals, called a
"carrier." These signals must occur before a data link is

At the default X4 setting, the modem sends your screen the
NO CARRIER message after 60 seconds. If you listen to the
speaker and realize you have received a voice answer, you
can respond immediately, instead of waiting for the modem to
time out, by pressing any key on the keyboard. This cancels
the call.

You can also hear if dialing is proceeding too quickly for
the system. Terminate the call (press any key) and retype
the Dial command, but insert a comma (,) or a couple of
slashes (/), to have the modem pause during the dialing

Volume Control (Ln)

The following options allow you to adjust the speaker volume
if you have an internal modem. You can adjust an external
modem's volume via its volume switch.

L0 Low.

L1 Low.

L2 Medium. Default.

L3 High.

Speaker Control (Mn)

This command disables the speaker entirely or sets the
speaker to monitor different segments of the dial-connect

M0 Disables the speaker entirely so that you don't hear
the modem go off hook, dial, etc.

M1 The speaker is on until Carrier Detect. Default. You
can monitor call progress until the Sportster detects
the remote modem's carrier signals, or until the 60-
second timeout and result code display. At Carrier
Detect, the modem disconnects the speaker and data-
transmission sounds are suppressed.

M2 The speaker is on continuously, including during data

M3 The speaker doesn't go on until after the last digit is
dialed, then goes off at Carrier Detect.


Local echo is the display of what you type at the keyboard
and online echo display of data the Sportster transmits to
another modem. The En command controls the display of your
typed commands, when the Sportster is in Command mode. The
Fn command controls the display of data when your modem is
online to another system.

Command Mode Local Echo (En)

The power-on/reset default for command mode local echo is

set with DIP switch 4. The Sportster modem is shipped with
DIP switch 4 OFF, enabling local echo of your typed

Use the En command to control the local echo for a current
session, independent of the switch setting. This command
may not be stored in NVRAM.

E0 Command mode echo OFF. The modem does not display
keyboard commands.

E1 Command mode echo ON.

NOTE: If double characters appear on the screen, both the
modem's and software's local echo are on.

Online Local Echo (Fn)

This command causes the modem to display a copy of the data
it is transmitting to another system. Many systems,
however, return a copy of received data, which is called a
remote echo. If the modem's online echo is ON and there is
also remote echoing, double characters appear on the screen.

In some microcomputer documentation, the term "duplex" is
applied to online local echoing, although the term is not
technically accurate.

F0 Online echo ON. Sometimes called "half duplex." As
the modem transmits data to a remote system, it also
sends a copy of the data to the screen.

F1 Online echo OFF. Sometimes called "full duplex."


The S-Registers are used to set various timing parameters
and to redefine selected ASCII characters and other
configuration options. Refer to the "Quick Installation
Guide" for a summary of S-Register functions and setting

Users typically require the default values. To change a
setting, use the ATSr=n command, where r is the register and
n is a decimal value from 0-255 (unless otherwise

The example below sets the modem's test timer (S-Register
18) to 10 seconds.


The modem does not perform a value-range check. Some values
you select may not work with some equipment, and you'll have
to readjust the settings.

Use ATSr? to display the contents of a register, as follows.



Four commands control the result codes that the modem
returns to the screen.

Vn Numeric/verbal response mode

Qn Display/suppress all result codes

Xn Result code options

&An Display/suppress additional result code options

Response Modes (Vn)

Result codes are sent to the screen in words (Verbal mode)
or numbers (Numeric mode).

The power-on/reset default for response modes is set with
DIP switch 2. The Sportster modem is shipped with DIP
switch 2 OFF, enabling Verbal mode.

Use the Vn command to select verbal or numeric result codes
for a current session, independent of the DIP switch
setting. This command may not be stored in NVRAM.

V0 Numeric mode. Numeric result codes are followed by a
Carriage Return but no Line Feed, as in the following
example, where a 3 is returned (for NO CARRIER).


V1 Verbal mode. Verbal responses are preceded and
followed by a Carriage Return and a Line Feed, as shown


Quiet Mode (Qn)

Enable/suppress the display of result codes.

The power-on/reset default for response modes is set with
DIP switch 3. The Sportster modem is shipped with DIP
switch 2 ON, to display result codes.

Use the Qn command to control the display for a current
session, independent of the DIP switch setting. This
command may not be stored in NVRAM.

Q0 Result codes are displayed.

Q1 Result codes are suppressed (made quiet).

Q2 Result codes are suppressed only in Answer mode.

Result Code Options (Xn)

You have five options, X0 through X4, for selecting the
result-code set best suited to your applications, as shown
in the tables below.

X0 Basic set, returns the first five codes (0-4) in the
following table.

X1 Extended set, codes 0-5, 10, 13 and 18, that adds rate-
specific CONNECT messages to the Basic set. This set
also includes all &An result codes.

X2-4 The default is X4. These options include the X1 set,
call-progress codes 6 or 7, and 8, and the functions
listed in the following table.

NOTE: By default, the modem is also set to &A3, which
selects additional results that report the protocols used in
the connection.

Result Code Options

Result Codes X0 X1 X2 X3 X4
0/OK o o o o o
1/CONNECT o o o o o
2/RING o o o o o
3/NO CARRIER o o o o o
4/ERROR o o o o o
5/CONNECT 1200 o o o o
7/BUSY o o
10/CONNECT 2400 o o o o
13/CONNECT 9600 o o o o
18/CONNECT 4800 o o o o
20/CONNECT 7200* o o o o
21/CONNECT 12000* o o o o
25/CONNECT 14400* o o o o
43/CONNECT 16800+ o o o o
85/CONNECT 19200+ o o o o
91/CONNECT 21600+ o o o o
99/CONNECT 24000+ o o o o
103/CONNECT 26400+ o o o o
107/CONNECT 28800+ o o o o
Adaptive Dialing o o o
Wait for 2nd Dial Tone (W) o o
Wait for Answer (@) o o
Fast Dial o o

* V.32 bis and V.FC modems only
+ V.FC modems only

NOTE: More CONNECT messages indicate an error control
connection, the call modulation, or the error control and
data compression used. See Additional Result Code Options
(&An), after this section.

Result Code Definitions

Result Code Meaning

0/OK Command has been executed.
1/CONNECT Connection established with another
modem; if set to X0, connection may be
300-28.8K bps; if X1 or higher,
connection is at 300 bps.

2/RING Incoming ring detected.

3/NO CARRIER Carrier detect has failed or carrier
has been dropped due to disconnect.

4/ERROR Command is invalid.

5/CONNECT 1200 Connection established with another
modem at 1200 bps.

6/NO DIAL TONE Dial tone not detected during the
normal 2 seconds, set in Register S6.

7/BUSY Busy signal detect; modem hangs up.

8/NO ANSWER After waiting 5 seconds for an answer,
modem hangs up; returned instead of
NO CARRIER when the @ option is used.

10/CONNECT 2400 Connection at reported rate. Same
for results of 4800 (18), 9600 (13),
7200 (20), 12K (21), 14.4K (25), 16.8K
(43), 19.2K (85), 21.6K (91), 24K (99),
26.4K (103), 28.8K (107).
NOTE: Connections over 9600 bps apply
to V.32 bis and V.FC modems only.
Connections over 14.4K bps apply to V.FC
modems only.

Adaptive (Hunt) The modem attempts to use tone
Dialing dialing and, if that doesn't work,
reverts to rotary (pulse) dialing.

Wait for Another The modem continues dialing as soon as
Dial Tone (W) it detects another dial tone.

Wait for an The modem continues dialing when it
Answer (@) detects 5 seconds of silence on the

Fast Dial The modem dials immediately on dial-
tone detect, instead of waiting the
normal 2 seconds set in Register S6.

Additional Result Code Options (&An)

Use this command to enable/disable one of the following sets
of error control, modulation, or protocol result codes.
If you encounter software problems, it may be because your
software expects to find different result codes from those
the modem is sending. (The modem defaults to &A3.) Review
your software documentation or try &A2, &A1, or &A0. You
may need to call your software's technical support to find
out which &An setting they support.

&A0 ARQ (error control) codes are disabled. This setting
does not affect an error control connection; the modem
returns standard CONNECT messages if result codes are

&A1 ARQ codes are enabled. CONNECT/ARQ is displayed if the
modem is set to X0 and the connection is 1200 bps and
above. The remaining results indicate connection rate
and require X1 or above. If your software cannot
handle the ARQ codes, select &A0.

&A2 V.32 modulation codes are enabled. These results
require a setting of X1 or higher. If your software
cannot handle the added modulation information, select
&A1 or &A0.

&A3 Protocol codes are enabled. Default. Error control
protocols reported are LAPM or MNP. When the call is
not under one of those protocols (and ARQ is not
included in the result code), the modem reports NONE,
for no protocol.

If the modems are using data compression, the type of
compression-V42BIS or MNP5-is added to the result code.

If your software cannot handle the added protocol
information, select &A2, &A1, or &A0.

Although these codes will return numeric identifiers if
DIP switch 2 is ON or you've set the modem to V0, they
are the same numeric identifiers used for &A2 result
codes. If you want &A3 protocol indicators, use Verbal
mode (V1), and not Numeric mode (V0).


By default, the Sportster first attempts a connection using
V.42 (LAPM) error control and, if that doesn't succeed, it
attempts an MNP connection. If that doesn't succeed, the
modem tries to connect without error control.

Error control is possible at rates of 1200 bps and above.

The following options are available.

NOTE: ARQ is U.S. Robotics' term for error control
protocols that feature error detection and automatic
retransmission of corrupted blocks of data.

&M0 Normal mode, no error control. Because of the nature
of phone-line channels, this is never recommended for
calls above 2400 bps unless you're using an error-
correcting file-transfer protocol.

&M1 Reserved.

&M2 Reserved.

&M3 Reserved.

&M4 Normal/ARQ mode. Default. If the remote modem doesn't
recognize the Sportster's error control signals--V.42
or MNP--the modem operates in Normal mode, as though it
were set to &M0.

&M5 ARQ mode. If the remote modem doesn't recognize the
error control request--V.42 or MNP--the Sportster hangs

Always set the Sportster for error control, &M4 (default) or
&M5, for calls at speeds over 2400 bps. Most users
communicating with V.42- or MNP-compatible modems will want
error control at 2400 and 1200 bps, as well.

If you're dialing out and have trouble connecting, it may be
because the remote modem doesn't have either MNP capability,
and it misinterprets your modem's MNP error control request.
If you know the remote modem doesn't support MNP, disable
MNP handshaking by setting Register S27 to 16 (ATS27=16).
The Sportster still connects, but without MNP error control.

To reset the modem for normal operations after the
call, issue the ATZ (reset) command, or set Register
S27 to zero.

Auto Answer with Error Control

When set to &M4 or &M5 and a call comes in, the modem goes
off hook and responds to received error control signals. If
the Sportster doesn't receive those signals and is set to
Normal/ARQ mode (&M4), it answers the call in Normal mode
(&M0). If it doesn't receive the signals and is set to ARQ
mode (&M5), it hangs up.


When data compression is enabled, the transmitting modem
detects redundant units of data and recodes them into
shorter units of fewer bits. The receiving modem
decompresses the redundant data units before passing them to
the receiving computer.

Compression does not occur unless the modems can establish
an error control connection.

If the Sportster makes a V.42 connection, it negotiates V.42
bis compression. If V.42 bis is not feasible, the
connection remains under error control, but without data

If the Sportster makes an MNP connection, it negotiates for
MNP Level 5 (MNP5) data compression. If the remote modem
does not have MNP5 capability, the connection remains
under MNP error control, but without compression.

&K0 Data compression disabled.

&K1 Auto enable/disable. Default. The modem enables
compression if the serial port rate is fixed (&B1) and
disables compression if the serial port rate follows
the connection rate (&B0). (Compression offers no
throughput advantage when serial port and connection
rates are equal, and may even degrade throughput.)

&K2 Data compression enabled. Use this setting to keep the
modem from disabling compression.

&K3 Selective data compression. The modem negotiates only
for V.42 bis compression, and disables MNP Level 5
(MNP5) compression. See the following note.

NOTE: MNP5 compression is not useful when transferring
already compressed files, such as the .ZIP files downloaded
from Bulletin Boards and 8-bit binary files that appear
already compressed to the modem. MNP5 tends to add data to
these files, and throughput over the phone link degrades.

V.42 bis compression detects when data is already compressed
and turns off until it detects that compression will be
advantageous. The special &K3 setting allows the best
throughput for already compressed and 8-bit binary files.


The &Bn and &Nn commands control data rates at the serial
port and phone line interfaces.

The Sportster defaults to a fixed rate at the serial port
interface (&B1) to keep the serial port rate higher than the
connection rate. You'll get greater throughput regardless
of the connection rate. Your software, however, must
support this feature and you must set your software to use a
fixed rate.

For the phone line, however, we recommend variable
connection rates (&N0). This lets the modem switch its
connection rate to match the rate of a remote modem, no
matter what that rate is. If the connection rate is fixed,
for example, at 9600 bps (&N6), the modem only connects with
modems operating at that rate. Of course, if your
application requires connections with modems at only one
rate, you may wish to set the modem to a fixed connection

Software Requirements
Both variable and fixed serial port rates require
communications software support. Most communications
programs support variable or fixed rates. Check your
software manual. Set your software BEFORE making calls.

Serial Port Rate (&Bn)

Initially, the modem's serial port rate depends on your
software setting. The modem uses the rate at which it
receives the AT command to determine the serial port rate;
after that it depends on its &B setting.

&B0 Variable serial port rates. The modem switches its
serial port rate to follow the connection rate
established with a remote modem. If your software has
Auto Baud Detect, turn it on. The software will switch
its serial port rate to match the connection rate.

&B1 Fixed serial port rate. Default. The modem detects
its serial port rate from your last AT command and
maintains it, whatever the connection rate.

Set your software to 115.2K, 57.6K, 38.4K, or 19.2K bps,
then set the modem to &B1 for the best throughput. Some
programs require that you turn off Auto Baud Detect to
fix the serial port rate. Others use the term Serial
Port Lock (yes or no).

The serial port rate MUST EQUAL OR EXCEED the
connection rate. Also, this setting requires
flow control, preferably hardware (&H1), to avoid
buffer overflow.

&B2 Fixed for ARQ calls/Variable for non-ARQ calls, Answer
mode only. When the modem goes off hook and answers in
ARQ mode, it shifts its serial port rate to the one
written to NVRAM, for example, 38.4K bps. In non-ARQ
mode, it acts as if set to &B0 when answering, and
switches its serial port rate to match the call's
connection rate.

This option is designed for installations such as
Bulletin Boards that receive calls from a wide variety
of modems, ranging from the very slow to those with the
Sportster 's advanced design.

Connection Rate (&Nn)

Use the &Nn command to select variable or fixed rates at the
phone-line interface. Variable rates let the modem connect
with a variety of remote modems, while fixed rates limit
calls to one connection rate.

&N0 Variable rates. Default. The Sportster negotiates
with the remote modem for the highest possible
connection rate, depending on the capabilities of the
remote modem. This is the recommended setting.

&N Fixed rate. The Sportster only connects if the remote
1-8 modem is operating at the same rate. If not, the
Sportster hangs up.

The fixed rate options are as follows.

&N1 300 bps &N5 7200 bps (V.32 bis/V.FC only)
&N2 1200 bps &N6 9600 bps
&N3 2400 bps &N7 12K bps (V.32 bis/V.FC only)
&N4 4800 bps &N8 14.4K bps (V.32 bis/V.FC only)

By fixing the connection rate, you can filter out calls at
other than a specific rate, for security or other reasons.


The modem uses either hardware or software flow control to
manage the amount of data stored in the buffers, thus
preventing buffer overflow.

The Sportster defaults to hardware flow control. This type
of flow control is performed between the modem and computer
with serial signaling.

Software flow control uses the standard ASCII Transmit OFF
(XOFF) character, Ctrl-S, and the Transmit ON (XON)
character, Ctrl-Q.

ASCII definitions are as follows.

XON Ctrl-Q ASCII 17 Decimal, 11 Hex
XOFF Ctrl-S ASCII 19 Decimal, 13 Hex

NOTE: Both your software and computer must support the flow
control you select. All 100% IBM PC-compatible computers
support hardware flow control, as do Apple computers
equipped with a Hardware Handshaking cable. However,
hardware flow control requires software support. Refer to
your software documentation to see what your software

When you have determined the type of flow control your
system supports, be sure to set your software appropriately
BEFORE transferring files.

Warning on Software Flow Control

In ordinary operations, the only characters the modem
recognizes during a call are the three plus symbols (+++) of
the escape code that return it to Command mode. But when
software flow control is enabled, the modem or computer also
looks for Ctrl-S or Ctrl-Q characters. IF THESE CHARACTERS
XON/XOFF characters and acts on them.

For example, XON/XOFF characters occur in binary files, and
are used by Xmodem-type protocols. They may also come from
the remote system. An XON from the remote system, after
your modem has sent an XOFF, can result in buffer overflow.

Software flow control may prove satisfactory if you're only
transferring text files; however, you may lose data if
XON/XOFF characters occur in the data stream from other

To select software flow control, write the &F2 configuration
template to Y1.

AT &F2 &W

Software Flow Control Precautions
If you can't use hardware flow control and are doing Xmodem-
type protocol or binary file transfers, select a protocol
that performs error correction, and turn off the modem's
error control (AT&M0).

Transmit Data Flow Control (&Hn)

This type of flow control regulates data your computer
transmits to the modem for transmission over the phone link.
The modem monitors its Transmit Data buffer as data comes
in. If the buffer nears 90% capacity, the modem signals
the computer to stop transmitting. When it has sent enough
data over the link to empty half the buffer, it signals the
computer to resume transmitting.

When it is Required
Transmit Data flow control should be enabled in the
following situations.

* You're using error control (any allowable rate above
300 bps), with or without data compression. If data is
resent due to errors, a continuous stream of data from
the computer could overflow the modem's buffer.

* The serial port rate is higher than the connection rate.
For example, the serial port rate is 38.4K bps and the
connection rate is 14.4K bps.

NOTE: Set your software to either hardware or software flow
control. Some programs also require that you turn off the
type you are not using.

&H0 Transmit Data flow control disabled.

&H1 Hardware flow control. Default. Your computer and
software must support Clear to Send (CTS). The modem
drops the Clear to Send (CTS) signal to the computer
when its buffer nears 90% capacity, and starts sending
CTS again when the buffer is about half full.

&H2 Software flow control. Your software must support
XON/XOFF signaling. The modem sends an XOFF to the
terminal when its buffer nears 90% capacity, and sends
an XON when the buffer is about half full. Default in
the &F2-Software Flow Control template.

&H3 Use both hardware and software flow control. Select
this option if you're not sure what your computer

NOTE: If possible, use hardware flow control. See "Warning
on Software Flow Control," earlier in this guide for

Received Data Flow Control

Two commands--&Rn (hardware) and &In (software)--control the
flow of received data passed by the modem to your computer.
Because computers handle incoming data more quickly than the
modem receives it over the phone line, most applications
won't need this.

Hardware Control (&Rn)
When your computer drops its Request to Send (RTS) signal,
the modem stops passing along received data. The computer
sends RTS again when it is ready to receive more data.

Your computer and software must support RTS. You cannot use
this type of flow control, however, if your software
requires a constant RTS signal.

NOTE: Use only for ARQ (error control) calls, because the
V.42 and MNP protocols control the data flow across the
phone link. During non-ARQ calls, however, there is no way
to signal the remote modem to stop sending data. If your
modem stops passing data to your computer and the remote
modem keeps sending, the Received Data buffer will overflow.

&R0 Reserved.

&R1 The modem ignores Request to Send (RTS). This setting
is required if your software does not support RTS.

&R2 Hardware flow control of received data enabled.
Default. The modem passes received data to your
computer only on receipt of the RTS signal.

Software Control (&In)
When you send the modem a Ctrl-S (XOFF) command from the
keyboard, the modem stops passing received data to your
computer. When you send a Ctrl-Q (XON) command, it resumes.

NOTE: Because of the risk of data loss, &I1-5 are
recommended only if your data does not have XON/XOFF control
characters. See "Warning on Software Flow Control" for

&I0 Disables XON/XOFF flow control of received data.
Recommended for non-ARQ calls.

&I1 The modem acts on your typed Ctrl-S/Ctrl-Q commands and
passes them to the remote computer. Not recommended
for non-ARQ calls. Use in ARQ mode only, but keep in
mind that XON/XOFF characters sent to the remote
computer may interfere with XON/XOFF signaling between
it and the remote modem. &I2 is preferred for ARQ

&I2 The modem acts on your XON/XOFF commands, but removes
them before sending data to the remote computer.
Default in the &F2--Software Flow Control template.
Recommended setting for ARQ mode, only. It ensures
that the remote computer does not confuse its modem's
XON/XOFF characters with yours.

If the call is not in ARQ mode, there is no flow
control on the phone link. If you send an XOFF to your
modem and it stops passing data, it has no way to tell
the remote computer and modem to stop sending for a
while, and your modem's buffer may overflow. See &I5
for another alternative.

&I3 Host Mode. Applies only to modems attached to HP
mainframes using the ENQ/ACK protocol. ARQ mode only.

&I4 Terminal Mode. Applies only to modems attached to HP
system terminals using the ENQ/ACK protocol. ARQ mode

&I5 Enables phone link flow control when the connection is
not under error control. Both modems must use &I5. In
ARQ mode, the modem operates as if set to &I2. It acts
on XON/XOFF commands, but does not pass them on to the
remote system.

In non-ARQ mode, the modem acts as if set to &I0. It
does not look for local XON/OFF commands, but does look
for any XON/XOFF characters coming in over the phone
link from the remote computer. The modem acts upon
them and drops them from the data stream.

Operators can signal the other modem to stop sending
and control phone link data flow to keep their modem's
buffer from overflowing, if both are set to &I5.


The parameters described below are directly affected by the
serial connection and DIP switch settings, and apply to
external modems only.

Carrier Detect (&Cn)

Like DIP switch 6, this command controls Carrier Detect (CD)
signaling from the modem to the computer.

The power-on/reset default for response modes is set with
DIP switch 6. The Sportster modem is shipped with DIP
switch 6 OFF, disabling override for normal operations.

Use the &Cn command to control Carrier Detect for a current
session, independent of the DIP switch setting. This
command may not be stored in NVRAM.

Check your communications software manual to find the
required setting.

&C0 CD override, CD always ON.

&C1 Normal CD operations. The modem sends a CD signal when
connecting with another modem and drops CD upon
disconnecting. Most communications software programs
require this setting.

Data Terminal Ready (&Dn)

Like DIP switch 1, this command controls the Data Terminal
Ready (DTR) signaling from the computer to the modem.

The power-on/reset default for DTR is set with DIP switch 1.
The Sportster modem is shipped with DIP switch 1 OFF,
disabling override for normal operations.

Use the &Dn command to DTR for a current session,
independent of the DIP switch setting. This command may not
be stored in NVRAM.

Check your communications software manual to find the
required setting.

&D0 DTR override, modem ignores DTR.

&D1 Reserved.

&D2 Normal DTR operations. The computer or terminal must
send a DTR signal or the modem won't accept commands.

Dropping DTR terminates a call. Most communications
software programs require this setting.

Data Set Ready (&Sn)

The modem sends your computer a Data Set Ready (DSR) signal.
(Data Set is industry jargon for modem.) Few, if any,
commercial communications programs require the modem to
control DSR (&S1). Leave the modem set for DSR override
(&S0), unless you know that your installation requires a
different setting.

&S0 DSR is always ON (override). Default.

&S1 In Originate mode, the modem sends DSR after dialing,
when it detects the remote modem's answer tone. In
Answer mode, it sends DSR after sending an answer tone.


Checking the Help screens is the first step to recovery.
These screens give you the information you'll need to
identify a problem. Once a problem is identified, it can
easily be solved.


The Inquiry command has eight options. The most commonly
used options display the following information.

ATI4 Current settings

ATI5 NVRAM settings

ATI6 Link diagnostics

I0 The modem returns a product code. If you have a
problem and call U.S. Robotics' Technical Support
Department, you may be asked for this product code.

I1 The modem performs a checksum of its read-only memory
(ROM) and returns the result to the screen. This
function is used only in factory testing. The modem
should always read the same number.

I2 The modem performs a test of its random-access memory
(RAM) and returns either the OK (0) or ERROR (4) result
code, followed by OK when the test is completed. You
may want to use this command as a checkpoint if the
modem appears to be malfunctioning.

I3 The modem returns a product identification string.

I4 The modem displays its current configuration.

I5 The modem displays the stored phone numbers and two
templates (Y0 and Y1) stored in nonvolatile random
access memory (NVRAM). Activate the second screen by
pressing any key.

I6 During a connection, the modem monitors and stores
information about link operations. When the call is
ended, you can request a diagnostic summary.

For calls under data compression, the number of
characters sent may be less than the number of octets
sent, due to buffering operations.

Most terms used in the display are self explanatory
except for the following:

Octets: Compressed data units. If the number of
octets is greater than the number of
characters sent, the modems probably used MNP5
compression on an already compressed file, and
the result was expanded data.

Blers: Errors in data and protocol blocks. If there
were many block errors, your receiver may have
experienced problems on the line.

Blocks Resent: These represent blocks the remote modem
resent due to the previous category, Blers.

Link Timeouts: Protocol detection problems;
communications were severed momentarily and
the modems probably recovered. This does
not indicate the retry timeout.

Link Naks: Negative acknowledgments (one or more

Data Compression: Indicates the type of data
compression negotiated for the call (V42BIS or
MNP5) or NONE. A V42BIS response includes the
size of the dictionary and the maximum string
length used, for example, 2048/32.

Fallback: Enabled/Disabled: indicates whether or not
the modems negotiated online fallback during
the connection sequence.

Protocol: Indicates the error control protocol
negotiated (LAPM, MNP, NONE).

Speed: The last rates at which the receiver/
transmitter were operating before

Disconnect Reason: Possible reasons the modem hung up
are as follows:

* DTR dropped--The DTE dropped the Data
Terminal Ready signal, terminating the

* Escape code--The operator sent the modem
the +++ escape code.

* Loss of carrier--The modem detected loss of
the remote modem's carrier and waited the
duration specified in Register S10 (default
is 0.7 seconds).

* Inactivity timeout--The modem detected no
activity on the line for the duration
specified in Register S19 (default is 0,
timer disabled).

* MNP incompatibility--The modem is set to
&M5 and the remote modem does not have MNP
compatibility, or there was an MNP
negotiation procedure error.

* Retransmit limit--The modems reached the
maximum of 12 attempts to transfer a data
frame without error.

* LD received--The remote modem sent an MNP
error control Link Disconnect request.

* DISC--The remote modem sent a V.42
Disconnect frame.

* Loop loss disconnect--The modem detected a
loss of current on the loop connecting
it with the telephone company central
office. This usually occurs because the
remote modem has hung up: the central
office drops current momentarily when
there is a disconnect at the other end of a
call. Unless Register S38 is set higher
than 0, the modem immediately hangs up at
loop loss.

* Unable to retrain--After several attempts,
disturbances on the phone line prevented
the modems from retraining
(resynchronizing), and they could no longer
transmit or receive data.

* Invalid speed--The modem is set to &N1 or
higher, for a fixed link rate, and the
remote modem is not operating at the same

* XID timeout--The modems failed to negotiate
the V.42 Detection (XID Exchange) phase.

* SABME (Set Asynchronous Balance Mode
Extended) timeout--The modems failed this
part of V.42 link negotiation.

* Break timeout--Incompatible processing of a
Break signal occurred.

* Invalid codeword--The modem received an
invalid V.42 bis (compression) frame.

* A rootless tree--The modem received an
invalid V.42 bis (compression) frame.

* Illegal command code--The modem received an
invalid V.42 bis (compression) frame.

* Extra stepup--The modem received an invalid
V.42 bis (compression) frame.

I7 The modem returns a product configuration. If you have
a problem and call U.S. Robotics' Technical Support
staff, you may be asked to read this screen.


This command allows you to view the contents of a particular
S-Register, as in the following example that requests the
contents of Register S0 ("On what ring will the modem



At this command, the modem returns the phone number stored
in NVRAM at position n, as in the following example that
includes a sample modem response.



At this command the modem displays the number stored in the
last-dialed number buffer.



Sportster modems provide four Help screens: summaries of
the basic AT command set, extended ampersand (&) command
set, Dial command options, and S-Register functions.

Stop/Restart Display
The following command stops the display. Hold down the
Control key and type S.


To restart the display, use the same command or press key>.

Cancel Display
Either of the following commands cancels the display.


Basic Command Set ($)

At AT$, the Sportster displays a screen that shows a partial
summary of the command set. A second screen, activated by
pressing any key, shows the remaining commands.

Ampersand Command Set (&$)

At AT&$, the Sportster displays a screen that shows a
partial summary of the extended ampersand command set. A
second screen, activated by pressing any key, shows the
remaining command set.

Dialing (D$)

At ATD$, the Sportster displays the Dial command summary.

S-Register Functions (S$)

At ATS$, the Sportster displays a screen that shows a
partial summary of the S-Register functions. A second
screen, activated by pressing any key, shows the remaining


Modem testing is available with the &Tn command and Register
16 (Dial test). All loopback testing conforms to ITU-T
Recommendation V.54.

NOTE: Only one test can be performed at a given time. If
you send a test command while the modem is in Test mode,
you'll receive an ERROR message.


The tests supported through the &Tn command include Analog
Loopback, Digital Loopback, and Remote Digital Loopback.
You can key in your own data during testing, or use the
modem's internal test pattern and error detector.

Always disable error control before testing. If the modem
is detecting errors and retransmitting the affected data,
your test results will be invalid.

Ending a Test--&T0, S18

Issue the &T0 command to terminate a test. Alternatively,
set Register S18 to a specified number of seconds, for
example, S18=10. When the 10 seconds are up, the modem
automatically ends the test and returns to Command mode. If
the test was Analog Loopback, the &T0 command hangs the
modem up. If the test was Digital or Remote Digital
Loopback, issue an ATH command to hang up the modem, or an
ATZ command to hang up the modem and reset it to its

NOTE: If you use the S18 test timer, but in the process of
testing you issue an ATZ command, S18 resets to zero and the
timer is disabled. Also, you cannot store a value for S18
in nonvolatile memory; its power-on and reset default is
always zero.

Analog Loopback-&T1, &T8

This test checks the operation of the modem's transmitter
and receiver.

This AL option requires that you type data you can later
verify at your screen.

1. The modem should be on hook in Command mode. If you
wish, set Register S18 as a test timer. For example,
insert S18=10 in the following command string before

AT &M0 S18=10 &T1

The modem disables error control, sets the timer, enters
Analog Loopback (AL) mode, and sends a CONNECT message.

2. Type recognizable data so that you can verify it when
it is looped back to the screen.

3. End the test. If you set S18, the modem automatically
stops the test at the timeout, exits AL mode and
responds OK.

If you didn't set Register S18, wait one second and type
+++ to end the test and return the modem to Command
mode. When the modem responds OK, type AT&T0 to
terminate AL mode and hang up the modem. (Typing ATH
has the same effect. Typing ATZ also has the same
effect, but also resets the modem and restores your &M

The modem responds OK. If the modem sends an ERROR
message, you have issued an invalid command.

4. If there were no errors, reset the modem to &M4, for
error control, unless you've issued the ATZ reset

NOTE: If the modem is in Online-Command mode--that is,
still connected to a remote modem--and you send it an
&T1 or &T8 command, it drops the call, enters AL mode,
sends a CONNECT result and waits for loopback

This AL option causes the modem to send an internal test
pattern to its transmitter and loop it back to the receiver.
An internal error detector counts any errors and, when the
test is ended, sends the number of errors or 000 (no errors)
to the screen.

Since you don't type anything during this test, and the
modem does not send anything to the screen, this option
verifies only the modem. If there are no errors but your
problem continues, it may be at the computer interface.

1. The modem should be on hook in Command mode. If you
wish, set Register S18 as a test timer. For example,
insert S18=10 in the following command string before

AT &M0 S18=10 &T8

The modem disables error control, sets the timer, and
enters AL mode. The modem sends its internal test
pattern to the transmitter, and loops the pattern back
to the receiver. You will not see any data on your

2. End the test. If you set S18, the modem automatically
stops the test at the timeout. If you didn't set
Register S18, type AT&T0 to end the test. Or use ATH
or the command that resets the modem, ATZ. Both of the
latter end the test and hang up the modem.

When the modem hangs up, it returns a three-digit code,
followed by OK. A code of 000 indicates no errors were
found. A code of 255 indicates 255 or more errors. An
ERROR message indicates that you issued an invalid

3. If there were no errors, reset the modem to &M4 for
error control unless you issued the ATZ command.


This option is reserved.

Digital Loopback-&T3

If your modem has passed the Analog Loopback (AL) test, this
test can help you locate a problem with a remote modem or
the telephone channel.

1. Set the modem to &M0 to disable error control.
Establish a connection with the remote modem.

2. Bring the modem back to Online-Command mode with the
+++ escape code. Then send it the AT&T3 command. The
modem enters Digital Loopback (DL) mode.

3. The remote user should type a short message. It will
be looped back by your modem's transmitter for
verification on the remote screen. You will not see the
message or any other data.

4. When the remote user has completed the test, issue the
AT&T0 command to end the test. If you wish, return the
modem online (ATO) to resume Data mode. Or type either
ATH or the command that resets the modem, ATZ. The
latter two commands end the test and hang up the modem.
The modem responds OK. If the modem sends an ERROR
message, you have issued an invalid command.

&T4, &T5

The &T4 option grants a remote modem's request for a Remote
Digital Loopback test.

The &T5 option cancels &T4 and your modem will not recognize
a request for a Remote Digital Loopback test from a remote
modem. This is the default so that your modem isn't subject
to another user calling and tying up your modem without your

Remote Digital Loopback-&T6, &T7

This test, like the Local Digital Loopback test, verifies
the condition of both modems and the phone link.

The request for and granting of Remote Digital Loopback
testing requires that both modems use ITU-T V.54 standard
signaling. The test MUST be performed at 2400 or 1200 bps.
If the remote modem does not have the capability or is not
set to respond, you will get an ERROR result code.

This RDL option requires that you send keyboard data to the
modem and verify it when it is returned over the phone lines
and to your screen.

1. Set your software to 2400 or 1200 bps. Set the modem to
&M0. If you wish, set the S18 timer.

Establish a connection with the remote modem. If you
haven't already done so, arrange with the remote user to
cooperate with your testing. The remote user should set
his or her modem to acknowledge the RDL request, for
example, AT&T4.

2. Bring the modem back to Online-Command mode with the
+++ escape code. Send it the AT&T6 command. The modem
enters RDL mode.

3. Type a short message. It will be looped back to your
modem by the remote modem and to your screen for
verification. (The remote user will not see your data.)

4. End the test. If you set Register S18 the modem
automatically ends the test when the test timeout is
reached. If you didn't set S18, type AT&T0 to end the
test. If you wish, return the modem online (ATO) to
resume Data mode. Or send either ATH or the command
that resets the modem, ATZ. The latter two commands end
the test and hang up the modem. The modem responds OK.
If you issue an invalid command, the modem sends an
ERROR message.

Data errors indicate a problem with the remote modem or
the phone link. If you have not performed analog loop-
back testing with your modem, the problem may also lie
with your modem.

5. Reset the modem to &M4 unless you used the reset
command, ATZ.

This test option causes the modem to send an internal test
pattern through the Remote Digital Loopback. An internal
error detector counts any errors and, when the test is
ended, sends the number of errors or 000 (no errors) to the

You don't need to type anything during this test. The modem
sends only its final error count to your screen.

1. Set your software to 2400 or 1200 bps. Set the modem
to &M0. If you wish, set the S18 timer.

Establish a connection with the remote modem. If you
haven't already done so, arrange with the remote user to
cooperate with your testing. The remote user should set
his or her modem to acknowledge the RDL request, for
example, AT&T4.

2. Bring the modem back to Online-Command mode with the

+++ escape code. Then send it the AT&T7 command. The
modem enters RDL mode. The modem sends its internal
test pattern to the remote modem, which loops it back to
your modem. You will not see the data on your screen.

3. End the test. If you set S18, the modem automatically
stops the test when the timer times out. If you didn't
set Register S18, type AT&T0 to end the test. After you
view the test results (next paragraph), return the modem
online if you wish (ATO) and resume Data mode. Or send
either ATH or the command that resets the modem, ATZ.
The latter two commands end the test and hang up the

When you terminate the test, the modem returns a three-
digit code, followed by OK. A code of 000 indicates no
errors were found. A code of 255 indicates 255 or more
errors. If you issue an invalid command, the modem
sends an ERROR message.

If you've performed an Analog Loopback and know your
modem is working properly, errors indicate a problem
with either the phone connection or the remote modem.

4. Reset the modem to &M4 unless you've sent it the ATZ
reset command.


The Dial test is used for factory-testing the frequencies of
tone dialing values. When S-Register 16 is set to 2 and a
single tone is dialed (for example, ATD7 ), the modem
continues to transmit that tone until you press Enter again.



Fax Modem Guidelines

Fax operations require facsimile-compatible software that
can send or receive Group III faxes. Follow the
instructions in your fax software manual.

The modem's normal operating mode is Data mode. If your fax
software is typical, it automatically switches the modem to
Fax mode when you run the program, and resets the modem to
Data mode when you exit the program.

If you have a problem, however, and think the modem may be
in the wrong mode, you can use one of the following AT
commands to manually switch the modem.

Most users will never need to use these commands.

AT+FCLASS=0 (Switch to Data mode)
AT+FCLASS=1 (Switch to Class 1 Fax mode)
AT+FCLASS=2.0 (Switch to Class 2.0 Fax mode)

If you are not sure whether the modem is in Data or Fax
mode, type the following command.


The modem returns a 0 to indicate Data mode, a 1 to indicate
Class 1 Fax mode or a 2.0 to indicate Class 2.0 Fax mode.

NOTE: Whenever the fax modem is reset using the ATZ
command, toggling the DTR signal, or turning the power off
and on, the modem will be set to Data mode.

Fax Mode Flow Control Setting

Many facsimile software products use software flow control
when the modem is in Fax mode. To allow compatibility with
software products that use software flow control by default,
U.S. Robotics fax modems switch to software flow control
when entering Fax mode.

For the best information on modem settings, see your Fax
software manual.

FCC Notice

FCC part 68, rules regarding fax operation, has been amended
as follows:

Telephone facsimile machines--identification of the
sender of the message: It shall be unlawful for any
person within the United States to use a computer or
other electronic device to send any message via a
telephone facsimile machine unless such a message clearly
contains, in a margin at the top or bottom of each
transmitted page or on the first page of the
transmission, the date and time it is sent and an
identification of the business, other entity, or
individual sending the message and the telephone number
of the sending machine or of such business, other entity,
or individual. Telephone facsimile machines manufactured
on and after December 20, 1992 must clearly mark such
identifying information on each transmitted page.

A Note to Programmers

If you want to know more about the supported fax commands,
refer to the standard for the Service Class 1 fax protocol.

ANSI/EIA/TIA-578-1990 (EIA-578)
Asynchronous Facsimile DCE Control Standard
November, 1990 Approved: October 22, 1990

You can obtain a copy of this standard by contacting Global
Engineering Documents, at 1-800-854-7179.

For more information on supported Class 2.0 fax commands,
refer to the standard for the Service Class 2.0 fax protocol.

ANSI/EIA/TIA-592-1993 (EIA-592)
Asynchronous Facsimile DCE Control Standard
May, 1993


When you install the Sportster, you have the option of
plugging your phone into the second modular jack of the
modem so it's available for voice calls. You can also use
the phone to set up communications with another user whose
modem uses the AT command set, such as a U.S. Robotics or
U.S. Robotics-compatible modem.


First call the other user to establish the parity, word
length, and number of Stop bits the other person's modem
accepts. Then turn the call over to your modems, as


1. Without hanging up the phone, have your modem go off
hook in Originate mode. Type the following command.


NOTE: Be sure the modem is NOT set to X2 or X4, or it
will return the NO DIAL TONE result code and hang up.

2. The other party should have the remote modem go off
hook in Answer mode. The following command is used to
do this.


3. Now both of you can hang up your respective phones
while the two modems establish the data link. They will
maintain the link until one of you gives your modem a
command to disconnect.

Either party's device can be the originate or answer
modem; it doesn't matter who made the phone call. But
one modem must enter Originate mode and the other Answer
mode. You and the other party, therefore, must agree on
which command, ATD or ATA, you will each use.



The Sportster modem conforms to the following standards,
ensuring compatibility with a wide base of installed modems.
ITU-T is the new signifier of what was formerly the CCITT
international standards body.

V.Fast Class 28.8K/26.4K/24K/21.6K/19.2K/16.8K/14.4K/
12K/9600/7200/4800 bps
(V.FC only)

ITU-T V.32 bis 14.4K/12K/9600/7200/4800 bps
(V.32 bis/V.FC modems only)

ITU-T V.32 9600/4800 bps

ITU-T V.22 bis 2400 bps

Bell 212A 1200 bps (also ITU-T V.22)

ITU-T V.23 1200 bps with 75 bps back channel
(Some United Kingdom and European
phone systems)

Bell 103 300 bps (ITU-T V.21 optional)

ITU-T V.42 LAPM error control, 1200 bps and higher

ITU-T V.42 bis Data compression, 1200 bps and higher

MNP Levels 2, 3 and 4 error control, level 5
data compression, 1200 bps and higher

ITU-T V.54 Analog, digital, and remote digital
loopback testing

Fax Modems
TIA/EIA-578 Service Class 1 Asynchronous
Facsimile DCE Control Standard

ITU-T V.17 14.4K/12K bps

ITU-T V.29 9600/7200 bps

ITU-T V.27 ter 4800/2400 bps

ITU-T V.21 300 bps


The serial interface information below applies only to
external modems.


The serial interface is a standard developed by the
Electronic Industries Association (EIA). It defines the
signals and voltages used when data is exchanged
between a computer and a modem or serial printer.

The entire standard covers many more functions than are used
in most data communications applications. Data is
transmitted between the devices over a shielded serial cable
with a 25-pin male (DB-25P) connector to the modem and a 25-
pin, 9-pin, 8-pin, or custom-built connector to the

NOTE: FCC regulations require the use of shielded cable
when connecting a modem to a computer to ensure minimal
interference with radio and television.

Pin Assignments

Pin assignments are factory-set in the Sportster modem to
match the standard DB-25 assignments in the following table.
DB-9 connectors for IBM PC/AT-compatible computers should be
wired at the computer end of the cable as shown in the DB-9

Serial Interface Pin Definitions

Signal Source
DB-25 DB-9 Circuit Function Computer -- Modem

1 * AA Chassis Ground Both
2 3 BA Transmitted Data Computer
3 2 BB Received Data Modem
4 7 CA Request to Send Computer
5 8 CB Clear to Send Modem
6 6 CC Data Set Ready Modem
7 5 AB Signal Ground Both
8 1 CF Carrier Detect Modem
12 * SCF Speed Indicate Modem
20 4 CD Data Terminal Ready Computer
22 9 CE Ring Indicate Modem

If you're using a Macintosh computer, ask your dealer for
the correct modem cable; we recommend a Hardware Handshaking

Macintosh 8-Pin DIN

Signal Source
DB-25 MAC Function Computer -- Modem

20/5* 1 Output Handshake* Computer/Modem*
4 2** Input Handshake Computer
2 3** Transmit Data Negative*** Computer
7 4 Ground Both
3 5 Receive Data Negative Modem
-- 6 Transmit Data Positive**** --
-- 7 Not connected --
-- 8 Receive Data Positive --

* Adds CTS capability when in Hardware mode.
** Hardware handshaking lines.
*** To do this, you must ground pin 6.
**** To do this, you must ground pin 8.

NOTE: A three-wire interface consists of Receive, Transmit,
and Ground wires and does not support hardware flow control.
Systems requiring three-wire interfaces must use software
flow control. If your system doesn't support software flow
control, use no flow control but be sure to use an error-
correcting protocol.

Minimum Requirements

Some computer equipment supports only a few of the serial
signal functions set in the Sportster modem. The minimum
required for the modem to operate is as follows.

Minimum Required Pins

DB-25 DB-9 8-Pin
Pin Pin DIN Function

2 3 3 Transmitted Data
3 2 5 Received Data
7 5 4 Signal Ground
20 4 1 Data Terminal Ready*

* Required if DIP switch 1 is OFF for normal DTR operations,
override disabled.

Additional Flow Control Functions
If your computer and software support Clear to Send (CTS)
and you wish to use Transmit Data hardware flow control
(&H1), Pin 5 (DB-25) or Pin 8 (DB-9) is required.

If your computer and software support Request to Send (RTS)
and you wish to use Received Data hardware flow control
(&R2), Pin 4 (DB-25) or Pin 7 (DB-9) is required.

For 115.2K, 57.6K and 38.4K bps Serial Port Rates
Your software and computer must support the 115.2K, 57.6K or
38.4K bps rate. Make sure the serial cable is shielded.
Cables are normally six feet long, but longer lengths are
possible. If you encounter problems with signal degradation,
try a shorter cable.

If you decide to build your own cable, use a
low-capacitance cable. To further minimize the capacitance,
connect only those functions (pins) that your application


Data Format

Both your software and the remote system must use the same
10-bit data format. If you don't know the setup of the
remote computer's modem, phone ahead to find out what
combination of word length, parity, and Stop bit is

Set your communications software to the required scheme.
Some communications programs use a kind of shorthand for
formats, such as 7-E-1 or 8-N-1. The modem detects the
format from the AT prefix of the next command it receives
from your keyboard or from your software.

Allowable Data Formats

Word Parity Stop
Length (1 Bit) Bits

7 Even, Odd, 1
Mark, Space
7 None 2
8 None 1

Template Settings

You can create one or two customized configurations and
store one of them at a time in nonvolatile random-access
memory (NVRAM) as your power-on/reset default using the
&Wn command. As long as DIP switch 7 is OFF when you power-
on or reset the modem, your defaults are loaded into the
modem's random-access memory (RAM). To view your NVRAM
settings, use the ATI5 command.

The Sportster modem is preconfigured in the factory for the
&F1--Hardware Flow Control template settings in NVRAM as Y0,
and the &F2--Software Flow Control template settings in
NVRAM as Y1.

Tables on the next pages list the settings of the permanent
configuration templates &F1 (default), &F2, and &F0, as well
parameters you can modify and store in the NVRAM
configuration templates.

&F1--Hardware Flow Control Template
Factory Default

Feature &F1 Settings

ITU-T/Bell Answer Sequence B0 ITU-T sequence
Online Echo F1 Online Echo OFF
Speaker Control M1 Speaker ON until
Pulse/Tone Dialing P Pulse Dialing
Result Code Options X4 All Result codes
ARQ Result Codes &A3 All protocol codes
Serial port Rate &B1 Fixed serial port
Guard Tone &G0 No guard tone
Transmit Data Flow Control &H1 Hardware flow
Modem Testing &T5 Deny remote digital
Received Data Hardware Flow Control &R2 Enabled
Received Data Software Flow Control &I0 Disabled
Data Compression &K1 Auto enable/disable
Error Control &M4 Auto select
Connection Rate &N0 Variable connection
Make/Break Ratio &P0 U.S./Canada ratio
Volume Control (internal) L2 Medium volume
Data Set Ready (DSR) &S0 DSR always on
Break Handling &Y1 Break clears
buffer; break
then goes to
remote modem

The following parameters are changed via your communications

Stored Phone Numbers &Zn=s
Word Length 8 bits*
Parity None*
Serial port Rate 19.2K bps*

* Initial Settings; match software settings of subsequent &W

The &F2 and &F0 templates largely resemble the &F1 template.
The tables below list only those settings that differ from
the &F1 template.

&F2--Software Flow Control Template

Feature &F2 Settings

Transmit Data Flow Control &H2 Transmit data
flow control
Receive Data Flow Control &R0 Received data
flow control
&I2 Received data
flow control

&F0--Low Performance Template

Feature &F0 Settings

Result Code Options X1 Basic subset
ARQ Result Codes &A1 ARQ codes enabled
Serial port Rate &B0 Variable serial
port rate
Transmit Data Flow Control &H0 Disabled
Receive Data Flow Control &R1 Disabled

The following parameters are changed via your communications

Word Length 7 bits*
Parity Even*
Serial port Rate 9600 bps*

* Initial Settings; match software settings of subsequent &W

NVRAM S-Register Options

NVRAM S-Register Options Template Settings

S0* Number of rings to answer on 1
S2 Escape code character 43
S3 Carriage Return character 13
S4 Line Feed character 10
S5 Backspace character 8
S6 Dial wait-time, sec. 2
S7 Carrier wait-time, sec. 60
S8 Dial pause, sec. 2
S9 Carrier Detect time, 1/10th sec. 6
S10 Carrier loss wait-time, 1/10th sec. 7
S11 Tone duration, spacing, msec. 70
S12 Escape code guard time, 1/50th sec. 50
S13 Bit-mapped functions 0
S14 Bit-mapped functions 0
S15 Bit-mapped functions 0
S19 Inactivity/hang up timer 0
S21 Break length, 1/100th msec. 10
S22 XON character 17
S23 XOFF character 19
S25 DTR recognition time, 1/100th sec. 5
S27 Bit-mapped functions 0
S28 V.21/V.23 fallback delay, 1/10th msec. 8
S34 Bit-mapped functions 6
S38 Disconnect wait time, sec. 0

NOTE: Bit-mapped registers have up to eight functions. See
instructions under S13 in Appendix A of the "Quick
Installation Guide."

* The valid range of rings that can be stored in NVRAM for
S0 is 1-255. S0=0 cannot be stored in NVRAM. Regardless of
the NVRAM setting, DIP switch 5 must be OFF for the modem to
be in Auto Answer mode at power-on/reset.



Modem is a term based on the concept of MOdulation and
DEModulation. A modem modulates (converts) digital data
(computer information) to analog data (fluctuations in tones
carried over a copper telephone wire). The information is
carried over a telephone network until it reaches its
destination, where another modem demodulates the analog
signals and converts them back to digital data so the
computer there can use the information.

This ability to use the telephone network for quick,
inexpensive data exchange is a powerful tool used by
businesses and individuals worldwide to expand
business and personal networks.


Modems come in all shapes and sizes and their ability to
communicate is based on the protocols they use, or rules
they follow to perform operations in identical ways. They
may be preset or reset physically (DIP switches) and
logically (communications software) to best communicate with
the modem they are transferring information to and receiving
information from.

Much of this is done automatically by the modems when they
initially contact each other. The calling modem contacts
the answering modem and introduces itself. The modems
communicate via a series of signals to identify the
appropriate protocol and speed for efficient data transfer.
The answering modem either accepts the call or rejects the
call. This transaction is called a "handshake."

Successful handshaking results in what is called "carrier."
When modems establish carrier, your modem sends a Carrier
Detect signal to your computer, indicating that the modems
are ready to transfer data. If they fail to connect, your
modem sends your computer a No Carrier message.


Poor line quality may cause a decrease in efficient data
transmission. In order to ensure the data sent and received
is reliable, error control was introduced by modem
manufacturers. The modems check each data block received,
and if something went wrong between locations, the receiving
device instructs the sending device to resend the affected

Modems send information at different rates, measured in bits
per second (bps). Today, the figures can be staggering. In
the most optimal situation, the Sportster can exchange data
as fast as 115,200 bps.

In most cases, though, the speed relies heavily on the
ability to adapt to line conditions at high speed. This
adaptability is the most important feature of the Sportster.


Modems send data via asynchronous communication. The
smallest data unit sent is made up of a defined word length
(7 or 8 bits each), a Start bit (a 0 that indicates where
the data unit begins), and one or two Stop bits.

Parity bits were the typical method of controlling errors
before cyclic redundancy check (CRC) error correction,
described below under :Error Control." A parity bit is
either a 1 (odd parity) or a 0 (even parity), depending upon
whether the data segment has an odd or even number of binary
digits. Some systems allow mark parity (parity is always
1--odd) or space parity (parity is always 0--even). Parity
bits are used less often now that CRC is common.

The setting 8-N-1 (word length=8, parity=None, stop bits=1)
has become the most common data format in data
communications. Both computers involved in a data transfer
must use the same parity, word length, and number of Stop
bits or connection isn't possible and garbage characters
will display. The software must first be set the same on
the computers at both ends of the data transfer before the
modems can operate effectively. A simple phone call
to determine the settings at the other end can clear this up
quickly and easily.

The requirement to specify parity setting, even if it is
None (*-N-1), assures that users with older systems can
still communicate with newer modems.


Another important aspect of modem communications is flow
control, which manages the amount of data stored in buffers.
Buffers are used to store information temporarily before it
is passed on to a computer or modem. Flow control is used
to prevent buffer overflow. The system uses either hardware
or software (control characters) flow control. U.S.
Robotics recommends the use of hardware flow control,
because actual data may be mistaken for the control
characters used in software flow control and the data may be


Error control protects the integrity of data transferred
over phone channels and is available for calls at 1200 bps
and above. It can be disabled, although high-speed calls
(above 2400 bps) should always be under error control. The
operations defined in an error control protocol include the

* Establishment of compatibility

* Data formatting into blocks

* Error detection through Cyclic Redundancy Checking (CRC)
CRC is based on algorithms that calculate a value for an
entire block of data. The CRC value attached to each
block sent must match the receiving modem's calculation.
If not, the remote modem sends a negative acknowledgment
to the sending modem.

* Positive acknowledgment of error-free blocks and
negative acknowledgment of corrupted data blocks

* Retransmission of corrupted data blocks

Always set the Sportster for error control, &M4 (default) or
&M5, for calls at speeds over 2400 bps.

The Sportster is set at the factory to &M4, causing it to
try for an error control connection and, if that isn't
possible, to proceed with the call in Normal mode. The
modem first tries for a V.42 connection, then an MNP
connection. The information below is based on the
Sportster's setting of &M4.

ITU-T V.42 Handshaking

The exchange of signals between two devices in order to
establish a communications link is called handshaking.
ITU-T V.42 includes a two-stage handshaking process.

* A Detection phase that is based on an exchange of
predefined characters.

* LAPM (Link Access Procedures for Modems) Negotiation.
In this phase, the modems identify their capabilities
concerning maximum data-block size and the number of
outstanding data blocks allowed before an acknowledgment
is required.

MNP Handshaking

This protocol is supported by the ITU-T V.42 Recommendation.
It was originally developed by Microcom, Inc., and is now in
the public domain.

MNP handshaking begins with an MNP Link Request sent by the
calling modem. If the remote modem doesn't recognize the
request, error control isn't possible.

Data Compression

If the modems successfully establish a V.42 connection, they
also negotiate for V.42 bis data compression. If they
successfully establish an MNP connection, they negotiate for
MNP5 data compression.

Modems using V.42 bis compression negotiate the following

* Dictionary size--that is, the amount of memory available
for compression table entries. (Entries are codes
devised for redundant data. The data is packed into
shorter data units, called code words, and unpacked by
the receiving modem.)

Possible sizes are as follows. U.S. Robotics modems use
11-bit, or 2048-entry dictionaries, but drop down if the
remote modem uses a 512- or 1024-entry dictionary.

Bits Entries
9 512
10 1024
11 2048

* Maximum string length of each entry.

As the dictionary fills, the modem deletes the oldest unused
strings. V.42 bis compression is more efficient than MNP5
compression, in part because it dynamically deletes unusable
strings. In addition, it works better with files that are
already compressed. These include .ZIP files downloaded
from many Bulletin Boards and 8-bit binary files, which
appear to the modem to be compressed.

MNP5 compression should not be used with such files because
it adds data to them, which lessens throughput. (The
additional data is stripped when the file is decompressed by
the remote modem.) When transferring such files, it's best
to set the modem to &K3. This allows V.42 bis compression
to work dynamically with the compressed data, but disables

Flow Control

Flow control of data from the computer is required under
error control for two reasons.

1. The transmitting modem buffers a copy of each frame it
transmits to the remote end until it is acknowledged by
the receiving modem.

2. If errors are encountered, the transmitting modem must
resend the corrupted data. This retransmission
activity, combined with the steady stream of data from
the computer, can overflow the buffer.

Online Fallback/Fall Forward

Under error control, if a disturbance on the phone line
causes an error to a data block, the receiving modem replies
with a negative acknowledgment. In response, the
transmitting modem retrieves a copy of the original data
block from its Transmit buffer, and every block it sent
after that block, and retransmits them. This keeps
the data error-free and in sequence.

However, there is a retransmit limit: the modems hang up if
line disturbances are so severe that one of the modems has
retransmitted the same block of data twelve times without a
positive acknowledgment.

Because high-rate calls are more vulnerable than
transmissions at 2400 bps and below, V.32 bis/V.FC modems
risk reaching the retransmit limit and hanging up. To
prevent this, one of the modems requests that they fall back
if necessary. When line conditions improve, the modems fall
forward to the next higher rate, up to the link rate of the

Online fallback/fall forward is defined in V.FC and ITU-T
recommendation V.32 bis for modems. The Sportster 9600,
however, is a V.32 modem. V.32 modems fallback to 4800 bps
and stay at that rate.


The following guidelines should help you to make the most of
your modem's advanced performance features. In many
instances, experimentation and experience will indicate what
works best for your applications.

Throughput is the volume of user information transferred per
second, without Start and Stop bits and other overhead
information. You'll obtain optimal throughput under the
following conditions.

1. Your communications software supports a fixed serial
port rate higher than the connection rate (for example,
setting your software to lock into the 38.4K bps rate,
and retaining the default &B1 setting).

2. The call is under data compression.

3. You're transmitting text files. Throughput is higher
for text files than other types of files, such as .EXE
or .COM binary files.

4. File transfer may be slowed down by a file-transfer
protocol. Many non-text files require a file-transfer
protocol, but throughput results vary. Certain public
domain file-transfer protocols, for example, have the
following effects.

Kermit Newer versions of Kermit support packets up
to 9K and a sliding window design to
eliminate turnaround delay. With earlier
versions, however, throughput may be severely
reduced due to short block lengths (possibly
under 128 bytes) and acknowledgment
turnaround time.

Xmodem Throughput may be reduced if your version
uses short block lengths, for example 128
bytes. Some versions use blocks of 1K byte,
which is much better, although overhead
(error control protocol information) still
affects overall throughput.

Ymodem This protocol is similar to Xmodem with 1K
byte block lengths, and allows multiple files
to be sent in one transfer.

The above protocols further reduce throughput during error-
control (ARQ) connections. The accuracy of the data is
checked twice, by the file-transfer protocol and the modem.
To avoid redundancy, disable modem error control by setting
the modem to &M0.

The most current version of Zmodem can yield the most
efficiency. Leave the modem at its error control default
(&M4) and data compression default, &K1. Zmodem performs
the same kind of compression as V.42 bis; it turns off its
compression if files are already compressed.

An alternative protocol is Ymodem-G, with the modem left at
its error control default, &M4. Ymodem-G assumes the modems
are handling error control. Overhead is minimal, with
throughput almost equal to that obtained with no file-
transfer protocol.

However, keep in mind that Ymodem-G is only useful if the
modems are using error control. In addition, follow this
recommendation only if your machine and software support
hardware flow control.

NOTE: Both modems must use the same protocol for data
transfer to take place.

WARNING: If you are using an X-, Y- or Zmodem-type
protocol, do NOT use the modem's software flow control.

Achievable Throughput Statistics

The table below indicates the maximum throughput, in
characters per second (cps), that can be expected under the
following conditions:

* Serial port rate set at 57.6K bps; modem set to &B1
Your software and computer must support 57.6K bps in
order to use that rate.)

* Connection (link) rate of 14.4K bps (assuming no
protective fallback to a lower speed is necessary)

* V.42 bis compression negotiated for the call, and the
default size 11-bit, 2048-entry dictionary

* Straight data (that is, not already compressed, and no
file-transfer protocol)

* Transmission from a fast (for example, 386) computer

Throughput (cps) if set to 14.4K bps

File Type MNP5 V.42 bis

Assembler or Compiler listing 2880 3840
Text file 2325-2625 3400-5760
Binary file: .EXE 2175-2400 2030-2600
Binary file: .COM 2100-2250 2050-2300
.ZIP files (common on BBS's)* 1500-1650 1700
Random binary 8-bit* 1460-1575 1700

* These files are already compressed or appear to the modem
to be compressed. Additional MNP5 compression causes
throughput lower than what can be expected using MNP without
compression. We recommend setting the modem to &K3 when
transferring these files, to allow V.42 bis but disable

The following table indicates the maximum throughput, in
characters per second (cps), that can normally be expected
in the same conditions as the previous table, but with a
serial port rate of 38.4K bps.

Throughput (cps) if set to 14.4K bps

File Type MNP5 V.42 bis

Assembler or Compiler listing 2880 3840
Text file 2325-2625 3400-3840
Binary file: .EXE 2175-2400 2030-2600
Binary file: .COM 2100-2250 2050-2300
.ZIP files (common on BBS's)* 1500-1650 1700
Random binary 8-bit* 1460-1575 1700

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