AOH :: USRMAN.TXT
Complete manual for a US Robotics Dual Standard modem
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COURIER HIGH SPEED MODEMS
APPENDIX A. LINK NEGOTIATION (HANDSHAKING)
AND ERROR CONTROL
This appendix includes detailed
information on how USRobotics HST and
V.32 bis modems negotiate with remote
modems for the rate and other
characteristics of each connection. You
may find it helpful if you are having
difficulty connecting with another
modem.
In addition, you'll find information on
error control and, especially useful,
some statistics and guidelines on using
the modem for the best throughput.
The following text relies on familiarity
with two terms used in this manual, ARQ
and DTE. ARQ (automatic repeat request)
designates a connection under error
control. DTE (data terminating
equipment) means the computer or
terminal to which the modem is attached.
LINK NEGOTIATION (HANDSHAKING)
During high-speed link negotiation,
timing and procedures depend on whether
the modem uses HST or V.32 bis
modulation, as follows.
HST Mode
DTE rate: 38.4K/19.2K/9600 bps (38.4K
or 19.2K required for 14.4K calls)
Modem settings: B1, &B1, &H1/&H2/&H3,
&M4/&M5, &N0
Link Negotiation and Error Control A-1
COURIER HIGH SPEED MODEMS
1. The modems begin handshaking by
training (synchronizing) at 2400 bps
and exchanging information on their
error control, data compression, and
speed capabilities.
2. Once the modems enable error control,
handshaking proceeds as follows. If
the remote modem is operating at 2400
bps or lower, the Courier stays at
2400 bps or falls back to match the
remote modem's slower rate.
If the remote modem is HST-compatible
and operating at a higher speed, both
modems shift up and train at 9600
bps. From there, if possible, they
shift up again to 12K bps and again
to 14.4K bps. Or they fall back to
7200 bps and again to 4800 bps, if
the remote modem is operating at one
of those lower speeds.
Initially, the high-speed channel is
allocated to the answering modem, the
450-bps channel to the calling modem.
This allocation reverses if the
calling modem has more data to
transmit than the answering modem.
Specialized High-Speed Connect
It's possible for two modems in HST mode
to connect directly at 9600, 12K or
14.4K bps, without 2400-bps handshaking.
However, this is only recommended for
faster connections in specialized
installations where the computer and
software manage error control. The
reason is that there can be no error
control because HST modems negotiate
A-2 Link Negotiation and Error Control
COURIER HIGH SPEED MODEMS
error control during 2400 bps
handshaking.
Both modems must be set as follows.
High speed handshaking requires a fixed
link rate: the modem only connects if
the remote modem is operating at the
same link rateê9600 (&N6), 12K (&N7), or
14.4K bps (&N8).
DTE rate: 38.4K/19.2K/9600 bps (38.4K
or 19.2K required for 14.4K calls)
Modem settings: B1, &B1, &H1/&H2/&H3,
&M0, &N6/&N7/&N8
HST Mode, Error Control Disabled
If error control is disabledêthat is,
the Courier HST is set to &M0 or the
remote modem isn't set for error control
and the Courier HST reverts to &M0êthe
Courier operates in one of the following
ways.
1. If set to &N0, it only connects at
2400 bps or lower. This ensures that
there will not be data transfer at
high speeds unless the call is
protected by error control.
Courier HST modems negotiate error
control during 2400 bps handshaking.
If they cannot connect under error
control, they stay at 2400 bps. Or,
if the remote modem is operating at a
lower rate, the Courier HST switches
to the lower rate.
2. If set to &N6, &N7 or &N8, the
Courier will handshake at the higher
speed, 9600, 12K or 14.4K bps, as
Link Negotiation and Error Control A-3
COURIER HIGH SPEED MODEMS
shown in the previous configuration
example, Specialized High-Speed
Connect. However, that configuration
example should only be used in the
special situation described, where
the system takes care of error
control.
NOTE: Without error control, there are
no high speed line reversals. The high
speed channel is always allocated to the
answering modem. Also, there is no
online fallback to protect the
connection on impaired lines.
V.32 bis Mode
The handshaking described immediately
following this paragraph adheres
precisely to the CCITT recommendation.
In addition, USRobotics V.32 bis modems,
when connecting with each other, use an
enhanced proprietary handshaking
procedure which allows them to connect
faster and to retrain faster during
calls. They must, however, establish a
V.42 error control connection. This
proprietary handshaking is described
after the next section, under USRobotics
V.32 bis to V.32 bis.
V.32 bis
NOTE: High speed calls are highly
vulnerable to errors unless the data is
protected by error control. The opera-
tions described below take place even if
one of the modems is not set for error
control, thereby prohibiting error
control for the call.
A-4 Link Negotiation and Error Control
COURIER HIGH SPEED MODEMS
DTE rate: 38.4K/19.2K bps
Modem settings: B0, &B1, &H1/&H2/&H3,
&M4/&M5, &N0
WARNING: Answering V.32 bis modems
shift their DTE rate up to 19.2K bps
(for 14.4K bps connections) if the
calling V.32 bis modem dials at 14.4K
or 12K bps. The answering V.32 bis
modem then sends data to its DTE at
19.2K bps. If your DTE is limited to a
rate of 9600 bps, disable high-speed
modulation by setting Register S34 to a
value of 3 (ATS34=3). The calling
modem will then shift down to 9600 bps
for a V.32, not V.32 bis, connection.
1. The answering modem first sends out a
2100 Hz answer tone identifying it as
a V.32 or V.32 bis modem. If the
calling modem recognizes the tone,
the modems connect at the highest
possible speed, usually 14.4K bps.
(If the calling modem is a V.32
modem, its maximum speed is 9600 bps,
and the modems may connect at that
rate. But see paragraph 3.)
2. If the calling modem doesn't
recognize the answer tone, the
answering modem then sends a 2250 Hz
answer tone used by 2400, 1200 or 300
bps modems. If the calling modem is
operating at one of those rates, the
modems connect at the calling modem's
rate.
3. If the modems don't connect as in
paragraph 1 or 2, the answering V.32
bis modem then sends extra V.32
answer tones. If the calling modem
Link Negotiation and Error Control A-5
COURIER HIGH SPEED MODEMS
is a V.32 modem, the answering V.32
bis modem shifts its speed down to
9600 bps and the modems connect at
that speed. This extended V.32
handshaking ensures connections with
V.32 modems if they did not connect
as in paragraph 1.
It may even be necessary to extend
the length of these tones if the
modem is to answer older, "dumb" V.32
modems. Register S28 is used to
modify the duration of these extra
V.32 tones. See S28 in Appendix B.
USRobotics V.32 bis to V.32 bis
1. The modems first negotiate a V.42
error control connection. Speed
negotiation is part of the V.42
detection/LAPM sequence. If they
fail to make a V.42 connection, these
modems follow the procedures
described under V.32 bis, above.
2. The Receiver of each modem dictates
its modem's highest speed, with
negotiation beginning at 7200 bps and
proceeding upward to the 14.4K bps
maximum. This means that your
modem's receiver may be operating at
a different speed from your modem's
transmitter, which operates at the
same rate as the remote modem's
receiver. In other words, the rate
at your modem's Originate frequency
may be different from the rate at
your modem's Answer frequency.
Because of this asymmetrical design,
one frequency may suffer line hits or
other impairments, and fall back to a
A-6 Link Negotiation and Error Control
COURIER HIGH SPEED MODEMS
slower speed, while the other does
not. The result is more efficient
line operation. If the impairments
are severe, the modems use normal
retraining.
Dual Standard Handshaking
Dual Standard modems always connect with
each other, either in HST mode or in
V.32 bis mode. However, we recommend
that Dual Standard modems be set to B0
and to &N0, so that they can connect
with V.32 bis, HST and lower-speed
modems, in both Originate and Answer
modes.
A Dual Standard modem set to B1 (HST)
does not send out any V.32 bis or V.32
answer tones, and therefore cannot
answer calls in those modes. When it is
calling, however, and set to B1, it
switches to V.32 bis mode if it detects
the V.32 bis/V.32 answer tone. It
attempts to connect at 14.4K bps (V.32
bis) or drops to 9600 bps (V.32). The
mode shift is for that call only.
Similarly, a Dual Standard modem set to
B0 will switch to HST mode for that call
only if the other modem is operating in
HST mode.
ERROR CONTROL AND THROUGHPUT
Overview
Error control is available for calls at
1200 bps and above. It can be disabled,
although high speed calls (above 2400
Link Negotiation and Error Control A-7
COURIER HIGH SPEED MODEMS
bps) should always be under error
control. The operations defined in an
error control protocol include the
following:
ù Establishment of compatibility
ù Data frame formatting
ù Error detection through Cyclic
Redundancy Checking (CRC)
ù Retransmission of corrupt data
frames
The Courier 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 following information
is based on the Courier's setting of
&M4.
A-8 Link Negotiation and Error Control
COURIER HIGH SPEED MODEMS
CCITT V.42 Handshaking
This international standard includes a
two-stage handshaking process:
ù A Detection phase that is based on
an exchange of predefined
characters.
ù 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 CCITT
V.42 Recommendation. It was originally
developed by Microcom, Inc. and is now
in the public domain.
MNP is based on special protocol frames.
If the remote modem doesn't recognize an
MNP Link Request, error control isn't
possible. (In HST asymmetrical mode,
USRobotics modems use a proprietary
scheme similar to MNP.)
Data Compression
If the modems successfully establish a
V.42 connection, they also negotiate for
V.42 bis data compression. If the they
successfully establish an MNP
connection, they negotiate for MNP5 data
compression. The type of compression
for a call, if any, is reported in the
ATI6 display.
Link Negotiation and Error Control A-9
COURIER HIGH SPEED MODEMS
Modems using V.42 bis compression
negotiate the following options and
report them in the ATI6 display.
ù 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.
USRobotics modems use 11-bit, or
2048-entry dictionaries, but drop
down if the
A-10 Link Negotiation and Error Control
COURIER HIGH SPEED MODEMS
remote modem uses a 512- or 1024-
entry dictionary. The size of the
dictionary for a call is reported
in the ATI6 display.
Bits Entries
9 512
10 1024
11 2048
ù 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 .ARC files downloaded from many
Bulletin Boards and 8-bit binary files,
which seem 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 MNP5.
Flow Control
Flow control of data from the computer
is required under error control for two
reasons:
Link Negotiation and Error Control A-11
COURIER HIGH SPEED MODEMS
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,
retransmission activity can cause a
steady stream of data from the
computer to overflow the buffer.
Throughput Guidelines
The following guidelines should help to
make the most of the modem's advanced
performance features. In many
instances, experimentation and
experience will indicate what works best
for your applications.
1. Optimal throughput is attained under
the following conditions:
ù The communications software allows
fixing the DTE rate higher than the
link rate, e.g., setting the soft-
ware to 38.4K or 19.2K bps and
setting the modem to &B1.
If the software automatically
switches bit rates to follow the
link rate, the modem's DTE rate
must be also set to follow the link
rate for each call, &B0, and
throughput will be limited.
Installations with specialized
software may want to enable a fixed
DTE rate for ARQ calls and a
variable DTE rate for non-ARQ
calls. See the &B2 command in
Chapter 4.
A-12 Link Negotiation and Error Control
COURIER HIGH SPEED MODEMS
ù The call is under data compression.
ù The data is comprised of text files
rather than binary files such as
.EXE or .COM files. See the table
at the end of this appendix.
2. MNP5 compression is disabled for
files that are already compressed and
8-bit binary files, that appear to
the modem to be already compressed.
MNP5 is disabled by setting the modem
to &K3.
3. The file transfer is not slowed down
by a file-transfer protocol. Many
non-text files require a file
transfer protocol, but the results
vary. For example, certain public
domain file transfer protocols have
the following effects:
Kermit Throughput is severely
reduced due to Kermit's short
block lengths (under 128
bytes) and acknowledgment
turn-around time.
Xmodem Throughput may be reduced if
your version uses short block
lengths (128 bytes). Some
versions user larger blocks
(1K blocks). Throughput is
also reduced by overhead
(error control protocol
information).
Ymodem There is an improvement over
Xmodem, due to larger block
lengths (1K bytes), but
throughput is still reduced
by the protocol's error
control overhead.
Link Negotiation and Error Control A-13
COURIER HIGH SPEED MODEMS
The above protocols further reduce
throughput when an error control
connection is established. The
accuracy of the data is checked
twice, by the file transfer protocol
and the modem. To avoid redundancy,
use the above protocols only for non-
ARQ connections, and only at speeds
of 2400 bps and below.
For the best throughput performance,
we recommend Ymodem-G and ZMODEM as
better choices, Ymodem-G being the
most efficient. These protocols
assume the modems are handling error
control: overhead is minimal, with
results almost equal to those when
there is no file transfer protocol.
Achievable Throughput
The table below indicates the maximum
throughput, in characters per second
(cps), that can be expected under the
following optimal conditions.
ù DTE rate set at 38.4K bps;
modem set to &B1
ù Connection (link) rate of 14.4K bps
ù V.42 bis compression negotiated for
the call, and the default size 11-
bit, 2048-entry dictionary
ù Straight data (e.g., not already
compressed, no file-transfer
protocol)
ù Transmission from a fast (e.g.,
286) computer
Throughput
(cps)
File Type MNP5 V.42 bis
A-14 Link Negotiation and Error Control
COURIER HIGH SPEED MODEMS
Assembler or Compiler listing 28
80 3840
Text file 2325-2625 3400-3840
Binary file: .EXE 2175-2400 2030-2600
Binary file: .COM 2100-2250 2050-2300
.ARC files (common on BBS's)* 1500-
1650 1700
Random binary 8-bit* 1460-1575 1
700
* These files are already compressed
or appear to the modem to be
compressed. Additional MNP5 compres-
sion 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 MNP5.
Throughput, MNP5 and V.42 bis
Link Negotiation and Error Control A-15
COURIER HIGH SPEED MODEMS
APPENDIX B. SUMMARIES AND TABLES
CONTENTS
The RS-232 Interface, with Pin
Definitions
Front Panel Indicators
DIP Switch Summary
Default Settings
S-Register Summary
ASCII Chart
Summaries and Tables B-1
COURIER HIGH SPEED MODEMS
THE RS-232 INTERFACE
DESCRIPTION
The RS-232 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 or terminal
and a modem or serial printer. Data is
transmitted between the devices via a
cable with 25-pin, 9-pin, 8-pin or
custom-built connectors.
PIN ASSIGNMENTS
The entire standard covers many more
functions than are used in most data
communications applications. Pin
assignments are factory set in the
Courier to match the standard DB-25
assignments in the following table. DB-
9 connectors for AT-compatible computers
should be wired at the computer end of
the cable as shown in the DB-9 column.
If you're using an Apple computer, ask
your dealer for the correct modem cable
for your Apple computer model.
Signal
Flow
DB-25 DB-9 Circuit Function D
TE ê DCE*
1 ê AA Chassis
Ground both directions
2 3 BA Transmitted Data to DCE
3 2 BB Received Data to DTE
4 7 CA Request to Send to DCE
5 8 CB Clear to Send to DTE
6 6 CC Data Set Ready to DTE
B-2 Summaries and Tables
COURIER HIGH SPEED MODEMS
7 5 AB Signal Ground both
directions
8 1 CF Carrier Detect to DTE
12 ê SCF Speed Indicate to DTE
15 ê DB Synchronous TX** Timing t
o DTE
17 ê DD Synchronous RX** Timing t
o DTE
20 4 CD Data Terminal Ready to DCE
22 9 CE Ring Indicate to DTE
24 ê DA Synchronous TX** Timing t
o DCE
* DTE indicates the terminal or
computer; DCE indicates the modem.
** Indicates Transmitter (TX) or
Receiver (RX)
RS-232 Interface Pin Definitions
Summaries and Tables B-3
COURIER HIGH SPEED MODEMS
Minimum Requirements
Some computer/terminal equipment
supports only a few of the RS-232 signal
functions set in the Courier. The
minimum required for the modem to
operate are as follows:
Asynchronous Calls
DB-25 DB-9
Pin Pin Function
2 3 Transmitted
Data
3 2 Received Data
7 5 Signal Ground
20 4 Data Terminal Ready*
* Required only if you have the Data
Terminal Ready Override switch OFF (DIP
switch 1 UP).
Synchronous Calls
You will need all of the above functions
as well as pin 15 for Transmitter timing
signals, and pin 17 for Receiver timing
signals. You may need pin 24, which is
assigned the external timing source,
rather than the internal (modem) source
assigned to pin 15. See Chapter 7 for
more detailed information.
Additional Flow Control Functions
If your computer and software support
Clear to Send and you wish to use
Transmit Data hardware flow control
(&H1), Pin 5 (DB-25) or Pin 8 (DB-9) is
required.
B-4 Summaries and Tables
COURIER HIGH SPEED MODEMS
If your computer and software support
Request to Send and you wish to use
Received Data hardware flow control
(&R2), Pin 4 (DB-25) or Pin 7 (DB-9) is
required.
FOR 38.4K DTE RATE
Your terminal or computer must support
the 38.4K rate. Make sure the RS-232
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 requires.
Summaries and Tables B-5
COURIER HIGH SPEED MODEMS
FRONT PANEL INDICATORS
SymbolMeaning Status
HS High Speed All calls above 2400 bps: ON
during call progress, after
completion of dialing; OFF
during HST-mode link
negotiations at 2400 bps,
then ON during connection.
Remains ON after disconnect
until next call is originated
or answered.
AA Auto Answer/ Answer mode only: ON when
your modem is
Answer in Auto Answer mode,
and when answering a call; in
HST mode, goes OFF if the
channel is reversed and your
answering modem transmits at
450 or 300 bps. Also goes
OFF when the modem originates
a call.
CDCarrier Detect ON if DIP switch 6 is UP
(factory setting) and the
Courier receives a valid data
signal (carrier) from a
remote modem, indicating that
data transmission is
possible. Also ON when the
CD override is on, DIP switch
6 DOWN.
OH Off Hook ON when the Courier takes
control of the phone line to
establish a data link.
RDReceived Data Flashes when the modem sends
result codes or passes
received data bits to the
computer or terminal.
B-6 Summaries and Tables
COURIER HIGH SPEED MODEMS
SD Send Data Flashes when the computer or
terminal sends a data bit to
the Courier.
TRData Terminal ON if DIP switch 1 is UP
(factory setting) and
Ready the modem receives a DTR
signal from the computer or
terminal. Also ON when the
DTR override is on, DIP
switch 1 DOWN.
MR Modem Ready/ ON when the Courier is
powered on.
Test Mode Flashes when the modems
retrain, including online
fallback, or while the modem
is in Test mode.
Summaries and Tables B-7
COURIER HIGH SPEED MODEMS
SymbolMeaning Status
RS Request to ON if your terminal or
software supports RTS
Send and sends the RTS signal.
OFF if the Courier is set to
&R2 (Received Data hardware
flow control) and the
computer or terminal lowers
RTS.
CSClear to Send ON until the modem lowers CTS
when Transmit Data hardware
flow control is enabled (&H1,
&H3). Always ON during
synchronous connections.
ARQError Control Automatic Repeat Request. ON
when the Courier is set to
&M4 or &M5 and successfully
connects with another modem
under error control. Flashes
when the Courier retransmits
data to the remote modem.
SYN Synchronous ON when the modem is set to
&M1 and
Mode enters synchronous mode.
B-8 Summaries and Tables
COURIER HIGH SPEED MODEMS
DIP SWITCH SUMMARY
PURPOSE
The DIP switches, located at the rear of
the modem, are for adapting the modem to
your equipment and personal require-
ments. The Settings Supplement that
comes with the modem indicates the
recommended switch settings for many
communications software packages. You
may also want to experiment and review
your software documentation as
necessary.
Some users are able to move a single
switch with a finger tip. If this
doesn't work for you, use a toothpick or
other small instrument.
OPERATIONS
The DIP switch settings are power-on
defaults, read by the Courier when it is
turned on. If changed when the modem is
on, switches 2-5, 7 and 9 require the
ATZ (software reset) command to initiate
the new settings. If you've set switch
8 UP to disable command recognition, and
want to return the modem to Smart mode
so that it responds to commands, you'll
have to power off the modem, reset
switch 8 DOWN, and power on the modem
again. The remaining (hardware)
switches are automatically operative
when set UP or DOWN.
Factory
SwitchSetting Function
Summaries and Tables B-9
COURIER HIGH SPEED MODEMS
1 OFF Data Terminal Ready Operations
OFF Normal DTR operations:
computer must provide DTR
signal for modem to accept
commands; dropping DTR
terminates a call
ON DTR always ON (Override)
2 OFF Verbal/Numeric Result Codes
OFF Verbal (word) results
ON Numeric results
B-10 Summaries and Tables
COURIER HIGH SPEED MODEMS
Factory
SwitchSetting Function
3 ON Result Code Display
OFF Results suppressed
ON Results enabled
4 OFF Command Mode Local Echo
OFF Keyboard commands
displayed
ON Echo suppressed
5 ON Auto Answer
OFF Modem answers on first
ring
ON Auto answer disabled
6 OFF Carrier Detect Operations
OFF Courier sends CD signal
when it connects with
another modem, drops CD on
disconnect
ON CD always ON (Override)
7 OFF Auxiliary, DIP Switch 3 ON
OFF Result codes in Originate
and Answer mode
ON Result codes in Answer
mode disabled
8 ON AT Command Set Recognition
OFF Command recognition
disabled (Dumb Mode)
ON Recognition enabled (Smart
mode)
9 OFF Escape Code (+++) Response
OFF Modem hangs up, returns to
Command mode, sends NO
CARRIER result
ON Modem maintains
connection, returns to
Summaries and Tables B-11
COURIER HIGH SPEED MODEMS
Command mode, sends OK
result
10 OFF Power-on and ATZ Reset
Software Defaults
OFF Load from nonvolatile
memory (NVRAM)
IB Load factory settings from
read only memory (ROM)
continued
B-12 Summaries and Tables
COURIER HIGH SPEED MODEMS
Factory
SwitchSetting Function
QUAD OFF RS-232 Transmit/Receive Pin
Assignments
SWITCH OFF Normal assignments; see
Pin Assignments in
Appendix B-1
ON Reversed Transmit/Receive
pins
The need to change this switch
setting is rare. Carefully
review your computer or
terminal documentation before
setting this switch DOWN.
Summaries and Tables B-13
COURIER HIGH SPEED MODEMS
DEFAULT SETTINGS
USER-PROGRAMMABLE DEFAULTS
You can create your own default
configuration and store it in
nonvolatile random access memory (NVRAM)
using the &W command described in
Chapter 5. As long as DIP switch 10 is
UP when you power on the modem, your
defaults are loaded into the modem's
random access memory (RAM). To view
your NVRAM settings at any time, use the
ATI5 command.
Tables on the next two pages list the
options you can store in NVRAM,
including S-Register settings. If DIP
switch 10 is DOWN at power-on, the
factory settings listed in the table are
loaded instead. The first time the
modem is turned on, the NVRAM settings
are the same as the factory settings.
The following command example
substitutes several user-defined
defaults for factory settings. The
modem also stores the rate, word length
and parity it detects from the AT
command prefix.
AT X4 &B1 &M5 &H1 M3 &W <Enter>
B-14 Summaries and Tables
COURIER HIGH SPEED MODEMS
NVRAM Options Factory Setting
Handshake option B0/B1 V.32 bis mode/HST
mode
Normal/error control modes &M4 Normal/ARQ
Data compression &K1 Auto enable/disable
Transmit data flow control &H0 Disabled
Rec'd. data hardware flow control &R1 Ignore
RTS
Rec'd. data software flow control &I0 Disabl
ed
DTE rate select &B0 Detect from AT
command; variable
Link rate select &N0 Variable
Result code subset X1 Extended
Error-control response codes &A1 Enabled
Tone/Pulse dialing P Pulse dial
Online local echo F1 Disabled
Speaker control M1 ON during dial
through connect
Remote Digital Loopback (RDL) &T5 Deny RDL
Normal/Leased line &L0 Normal phone line
Data Set Ready override&S0 Enabled
Synchronous clock source&X0 Modem
transmitter
Break handling &Y1 Clear buffer, send
immediately
Stored telephone number&Z0-3=0 Blank
Pulse dial make/break ratio &P0 U.S./Canada
Guard tone &G0 U.S./Canada
Rack Controller Unit (RCU) Access %R0 RCU
access disabled
Word length* 7
Parity* 1 Even
DTE rate* 19.2K
* Detected by the modem from the AT
prefix of the &W command that writes
Summaries and Tables B-15
COURIER HIGH SPEED MODEMS
your defaults to NVRAM. Set your
software to the desired word length,
parity, and DTE rate defaults before
sending the modem the AT . . . &W
string.
B-16 Summaries and Tables
COURIER HIGH SPEED MODEMS
Factory
NVRAM S-Register Options Setting
S2 Escape code character 43
S3 Carriage Return character13
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
S10Carrier loss wait-time, 1/10th
sec. 7
S11Touch-Tone duration, spacing,
msec. 70
S12Escape code guard time, 1/50th
sec. 50
S13 Bit-mapped functions 0
S15 Bit-mapped functions 0
S19 Inactivity/hang up timer 0
S21Break length, 1/100th msec. 1
0
S22 XON character 1
7
S23 XOFF character 1
9
S24Pulsed DSR duration, 2/100th sec.
150
S26RTS/CTS delay time, 1/100th sec.
0
S27 Bit-mapped functions 0
S28V.32 handshake time, 1/10th sec.
8
S32 Talk/Data Switch Options 1
S34 Bit-mapped functions 0
S38 Disconnect wait time, sec. 0
* Bit-mapped registers have up to eight
functions. See Appendix B-5 in the
manual or the briefer summary in the
Quick Reference Card.
Summaries and Tables B-17
COURIER HIGH SPEED MODEMS
S-REGISTER SUMMARY
USAGE
The default values are those users
typically require. Change the settings
with the ATSr=n command, where r is the
register and n is a decimal value from
0-255:
ATS13=8 <Enter>
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.
To display the contents of a register,
use ATSr? as in this example:
ATS20? <Enter>
Register Default Function
S0 See DIP Sets the number of rings
on which to
Switch 5 answer when in Auto Answer
Mode. S0=0 disables Auto
Answer, the same as DIP
switch 5 DOWN (factory
setting). S0=1 enables
Auto Answer and the modem
answers on the first ring.
S1 0 Counts and stores the
number of rings from an
incoming call.
S2 43 Stores the ASCII decimal
code for the escape code
character. Default
B-18 Summaries and Tables
COURIER HIGH SPEED MODEMS
character is +++. A value
of 128-255 disables the
escape code.
S3 13 Stores the ASCII decimal
code for the Carriage
Return character.
S4 10 Stores the ASCII decimal
code for the Line Feed
character.
S5 8 Stores the ASCII decimal
code for the Backspace
character. A value of
128-255 disables the
Backspace key's delete
function.
Register Default Function
S6 2 Sets the number of seconds
the modem waits before
dialing. If set to X2,
X4, or X6, the modem
ignores this register and
dials as soon as it
detects a dial tone (fast
dials).
S7 60 Sets the number of seconds
the modem waits for a
carrier. May be set for
much longer duration if,
for example, the modem is
originating an
international connection.
S8 2 Sets the duration, in
seconds, for the pause (,)
option in the Dial command
and the pause between
Summaries and Tables B-19
COURIER HIGH SPEED MODEMS
command re-executions (>
and A> commands).
S9 6 Sets the required
duration, in tenths of a
second, of the remote
modem's carrier signal
before recognition by the
Courier.
S10 14 Sets the duration, in
tenths of a second, that
the modem waits after loss
of carrier before hanging
up. This guard time
allows the modem to
distinguish between a line
hit, or other disturbance
that momentarily breaks
the connection, from a
true disconnect (hanging
up) by the remote modem.
While we do not recommend
connecting the modem to a
line with call waiting, if
you have call waiting you
may wish to adjust this
setting upward to prevent
the modem from
misinterpreting the signal
for a second call as a
disconnect by the remote
modem. A better
alternative is to contact
your phone company to find
out how to temporarily
disable call waiting.
S11 70 Sets the duration and
spacing, in milliseconds,
of dialed Touch-Tones.
B-20 Summaries and Tables
COURIER HIGH SPEED MODEMS
S12 50 Sets the duration, in
fiftieths of a second, of
the guard time for the
escape code (+++)
sequence.
Summaries and Tables B-21
COURIER HIGH SPEED MODEMS
Register Default Function
S13 0 Bit-mapped register.
Select the bit(s) you want
on and set S13 to the
total of the values in the
Value column. For
example, ATS13=20 enables
bit 2 (value = 4) and bit
4 (value = 16).
BitValue Result
0 1 Reset when DTR
drops
1 2 Reverse normal Auto
Answer operation:
on incoming RING,
enter Originate
Mode and look for
Answer tone
2 4 Disable 250 msec.
pause before result
code display
3 8 On DTR signal, Auto
Dial the number
stored in NVRAM at
position 0
4 16 At power on/reset,
Auto Dial number
stored in NVRAM at
position 0
5 32 Disable HST (used
for testing V.32
bis in Dual
Standard modems)
6 64 Disable MNP Level 3
(used for testing
Level 2)
7 128 Custom applications
S14 0 Reserved.
B-22 Summaries and Tables
COURIER HIGH SPEED MODEMS
Register Default Function
S15 0 Bit-mapped register. To
set the register, see the
instructions for S13.
BitValue Result
0 1 Disable the modem's
extra high-
frequency
equalization if it
causes problems on
shorter-link
callsêHST modems
only
1 2 Disable online
fallback
2 4 Disable 450 bps
back channel
3 8 Reset non-ARQ mode
Transmit buffer
from 1.5K bytes to
128*
4 16 Disable MNP Level
4; retransmitting
the larger Level 4
data blocks may be
a problem if you
expect a great
number of errors
during a call
5 32 Set backspace key
to delete
6 64 Some earlier 2400-
bps MNP modems, not
made by USRobotics
or Microcom, were
not fully
compatible with the
MNP protocol. If
you have difficulty
making a successful
2400-bps MNP
Summaries and Tables B-23
COURIER HIGH SPEED MODEMS
connection with a
remote MNP modem,
it may be because
of this incompati-
bility. Set S15 to
64 and try again to
make the
connection.
7 128 Custom applications
only
* The default 1.5K byte non-ARQ buffer
allows data transfer with X- and Ymodem-
type file transfer protocols without
using flow control.
The 128-byte option allows remote users
with slower modems to stop data you're
transmitting from scrolling off their
screens. When remote users send your
computer an XOFF (Ctrl-S) and you stop
transmitting, the data in transit from
your modem's buffer doesn't exceed the
size of their screen.
B-24 Summaries and Tables
COURIER HIGH SPEED MODEMS
Register Default Function
S16 0 Bit-mapped test register.
To set the register, see
the instructions for S13.
For information on
testing, see Appendix F.
BitValue Result
0 1 Analog Loopback
1 2 Dial test
2 4 Test pattern
3 8 Remote Digital
Loopback
4 16 Reserved
5 32 Reserved
6 64 Reserved
S17 0 Reserved.
S18 0 Test timer for software-
initiated loopback testing
(&Tn), disabled when S18
is set to 0. See Appendix
F. Used to set the
duration of testing, in
seconds, before the modem
automatically times out
and terminates the test.
S19 0 Sets the duration, in
minutes, for the
Inactivity Timer. The
timer activates when there
is no data activity on the
phone line and at the
timeout the modem hangs
up. S19=0 disables the
timer.
S20 0 Reserved.
Summaries and Tables B-25
COURIER HIGH SPEED MODEMS
S21 10 Sets, in 10-millisecond
units, the length of
Breaks sent from the modem
to the DTE. Applies to
ARQ mode only.
S22 17 Stores the ASCII decimal
code for the XON
character.
S23 19 Stores the ASCII decimal
code for the XOFF
character.
S24 150 Sets the duration, in 20-
millisecond units, between
pulsed DSR signals when
the modem is set to &S2 or
&S3. The default is 3
seconds.
B-26 Summaries and Tables
COURIER HIGH SPEED MODEMS
Register Default Function
S25 0 Reserved.
S26 1 Sets the duration, in 10-
millisecond units, of the
delay between RTS and the
modem's CTS response in
synchronous mode.
S27 0 Bit-mapped register. To
set the register, see the
instructions for S13.
BitValue Result
0 1 Enable CCITT V.21
modulation at 300
bps for overseas
calls. In V.21
mode, the modem an-
swers both Bell 103
and V.21 calls, but
only originates
V.21 calls.
1 2 Enable unencoded
(non-trellis-coded)
modulation in V.32
mode; this option
is part of the
CCITT V.32
recommendation, but
is rarely used.
2 4 Disable V.32
modulation; used
for testing HST
modulation in Dual
Standard modems.
3 8 Disable 2100 Hz
answer tone to
allow two V.42
modems to connect
more quickly.
4 16 See below.
Summaries and Tables B-27
COURIER HIGH SPEED MODEMS
5 32 See below.
6 64 Reserved.
7 128 Unusual software
incompatibility.
Some software may
not accept 7200,
12000 and 14400 bps
result codes. This
setting disables
the codes and
displays the 9600
code instead. The
call's actual rate
can be viewed on
the ATI6 screen.
continued on following page
B-28 Summaries and Tables
COURIER HIGH SPEED MODEMS
Register Default Function
Error control handshaking
options: select the total
values of bits 4 and 5.
Bit 4Bit 5 Result
0 0 Complete
handshaking
sequence: V.42
Detection, LAPM
error control, MNP.
16 0 Disable MNP.
0 32 Disable V.42
Detection and LAPM.
16 32 Disable Detection
phase, if you know
that the remote
modem does LAPM,
but not the
Detection phase.
S28 8 Sets the duration, in
tenths of a second, of the
extra 3000/600 Hz answer
tones sent during V.32
handshaking. Default = 8
(.8 seconds). This gives
V.32 modems additional
time to connect in V.32
mode before timing out.
If there is difficulty
answering older, manually
operated V.32 modems, for
example, modems that
require a button to be
pushed in order to dial,
try lengthening the
duration of the extra
tones.
Summaries and Tables B-29
COURIER HIGH SPEED MODEMS
Setting S28 to zero
eliminates the extra
tones, resulting in a
faster connect time if,
for example, the modem is
set to use V.21 modulation
(300 bps) or V.23
modulation (1200 bps).Sets
the duration, in 1/10ths
of a second, of the V.32
handshake.
B-30 Summaries and Tables
COURIER HIGH SPEED MODEMS
Register Default Function
S32 1 Sets the function for the
Voice/Data switch. This
is not a bit-mapped
register. Select the
value for the desired
function, for example,
ATS32=6.
Value Result
0 Disabled
1 Voice/data,
Originate mode
2 Voice/data, Answer
mode
3 Redial last number
4 Dial number stored
at
position 0
5 Auto Answer on/off
toggle
6 Reset the modem
7 Initiate Remote
Digital Loopback
S34 0 Bit-mapped register. See
instructions for S13.
BitValue Result
0 1 Disable V.32 bis.
Used for
troubleshooting;
USRobotics'
Technical Support
may require that
you disable V.32
bis for testing
purposes.
1 2 Disable the modem's
enhanced, propri-
etary V.32 bis
modulation. Used
Summaries and Tables B-31
COURIER HIGH SPEED MODEMS
for
troubleshooting.
2 4 Disable the faster
retrains that occur
during proprietary
V.32 bis
modulation. Used
for trou-
bleshooting.
3 8 Enable V.23.
Required for some
British
connections.
4 16 Change MR LED to
DSR
5 32 Enable MI/MIC; see
Appendix E-5.
6 64 Reserved
7 128 Reserved
B-32 Summaries and Tables
COURIER HIGH SPEED MODEMS
Register Default Function
S38 0 Sets the duration, in
seconds, before a forced
hang-up and clearing of
the Transmit buffer, when
DTR drops during an ARQ
call. This is provided to
allow time for a remote
modem to acknowledge
receipt of all transmitted
data. Default = 0: the
modem immediately hangs up
when DTR drops. If the
modem receives the ATH
command, it ignores S38
and immediately hangs up.
Summaries and Tables B-33
COURIER HIGH SPEED MODEMS
ASCII CHART
B-34 Summaries and Tables
COURIER HIGH SPEED MODEMS
APPENDIX C. ALPHABETICAL COMMAND SUMMARY
Additional command summaries are on the
bottom panel of the modem and in the
Quick-Reference Card.
REQUIREMENTS
1. Type commands in either upper
or lower case, not a combination.
2. All commands except A/, A> and
+++ are preceded by the AT prefix
and are executed with the
Enter/Carriage Return key
(<Enter>).
3. Command length = 40 characters
maximum. The modem doesn't count
the AT prefix, Carriage Return
character, or spaces. It counts
but doesn't act on punctuation such
as hyphens and parentheses.
4. A missing numeric parameter is
assumed to be zero, as in the
command to hang up: ATH <Enter> is
the equivalent of ATH0 <Enter>.
BASIC COMMAND SET
& See the Extended Command Summary that
follows this Basic Set.
% See the Percent Command Summary that
follows the Extended Command Summary.
A Force Answer mode when the modem hasn't
received an incoming call.
A/ Re-execute the last issued command one
time. A/ doesn't take the AT prefix or
a Carriage Return.
Command Summary C-1
COURIER HIGH SPEED MODEMS
A> Re-execute the last issued command
continuously until canceled by pressing
<any key>. Dial strings are re-executed
ten times, after which execution
terminates. A> doesn't take the AT
prefix or a Carriage Return.
Any key Terminate current dialing operation
resulting from an issued Dial command;
terminate Repeat mode (> or A>).
AT Attention: lets the modem know commands
are being issued to it. Must precede
all other commands except A/, A> and
+++.
Bn Handshake options.
B0 a) V.32 bis modulation (includes
V.32 answer tones). Courier V.32
bis: Default. Courier HST Dual
Standard: Required to answer V.32
bis calls. To call V.32 bis modems,
may be set to B0 or B1. HST
modulation remains enabled. Courier
HST: See next paragraph. HST
modulation remains enabled.
b) CCITT V.25 answer sequence.
Required for all Courier modems
answering overseas calls at 1200 bps
and above.
B1 a) HST modulation (no V.32 bis
answer tones). Courier HST:
Default. Courier HST Dual Standard:
Default. Also calls, but does not
answer, V.32 bis modems. Courier
V.32 bis: Calls, but does not
answer, V.32 bis modems.
b) Bell answer tone, United States
and Canada.
C-2 Command Summary
COURIER HIGH SPEED MODEMS
Cn Transmitter enabled/disabled.
C0 Transmitter disabled; receive-only
condition.
C1 Transmitter enabled (Default).
D Dial the number that follows and enter
Originate mode. Optional parameters:
P Pulse dial (Default).
T Touch-Tone dial.
, (Comma) Pause for 2 seconds.
; Return to Command mode after
dialing.
" Dial the letters that follow.
! Transfer call (flash switch-hook).
W Wait for second dial tone (with X3
or higher).
@ Wait for an answer (with X3 or
higher).
R Reverse frequencies.
DL Dial the last-dialed number.
DSn Dial the phone number stored in NVRAM at
position n (n = 0-3).
En Command mode local echo (display) of
keyboard commands ON/OFF. DIP switch 4
is factory set to Command mode echo ON.
E0 Local echo OFF.
E1 Local echo ON.
Command Summary C-3
COURIER HIGH SPEED MODEMS
Fn Online local echo of transmitted data
ON/OFF. Sometimes referred to as the
Duplex setting.
F0 Local echo ON. Sometimes called
Half Duplex. Modem sends a copy to
your screen of data it sends to the
remote system.
F1 Local echo OFF (Default). Sometimes
called Full Duplex. Receiving
system may send a remote echo of
data it receives.
Hn On/off hook control.
H0 Hang up (go on hook).
H1 Go off hook.
In Inquiry.
I0 Display product code.
I1 Display results of ROM checksum.
I2 Display results of RAM test.
I3 Display call duration or real time
(see Kn).
I4 Display current modem settings.
I5 Display nonvolatile random access
memory (NVRAM) settings.
I6 Display link diagnostics.
I7 Display product configuration.
Kn Modem clock operation: Call-duration or
Real-time mode.
C-4 Command Summary
COURIER HIGH SPEED MODEMS
K0 Return call duration at ATI3
(Default).
K1 Return actual time at ATI3. Clock
is set using ATI3=HH:MM:SS K1.
Command Summary C-5
COURIER HIGH SPEED MODEMS
Mn Monitor (speaker) control.
M0 Speaker always OFF.
M1 Speaker ON until carrier is
established (Default).
M2 Speaker always ON.
M3 Speaker ON after last digit dialed
and until carrier is established.
O Return online after command execution.
O0 Return online (normal).
O1 Return online and retrain. Use if
there were errors in a non-ARQ data
transfer.
O2 Return online, initiate a 2400 bps
speed shift, and drop down to 1200
bps. Applies only to calls at 2400
bps, and may be used if the remote
modem is a V.22 bis modem and ATO1
didn't work. Used mainly for
testing purposes.
P Pulse dial (Default).
Qn Quiet mode: result codes
displayed/suppressed. DIP switch 3 is
factory set for result code display.
Q0 Result codes displayed.
Q1 Result codes suppressed (quiet).
Q2 Result codes suppressed in Answer
mode.
C-6 Command Summary
COURIER HIGH SPEED MODEMS
Sr=n Set S-Register value: r is any S-
Register; n must be a decimal number
between 0 and 255.
Sr.b = n Alternative command for setting bit-
mapped registers: r is the bit-mapped
register; .b is the bit; n is 0 (off) or
1 (on).
Sr? Query contents of register r.
T Tone dial.
Vn Return result codes in words or numbers
(Verbal/Numeric mode). DIP switch 2 is
factory set for verbal result codes.
V0 Numeric mode.
V1 Verbal mode.
Xn Result code set options. Use the
following table (Default = X1, Extended
set, codes 0-5, 10, 13, 18).
Command Summary C-7
COURIER HIGH SPEED MODEMS
Setting
Result Codes X0 X1 X2 X3 X4
X5 X6 X7
0/OK + + + + + + + +
1/CONNECT + + + + + + + +
2/RING + + + + + + + +
3/NO CARRIER + + + + + + + +
4/ERROR + + + + + + + +
5/CONNECT 1200 + + + + + + +
6/NO DIAL TONE + + + +
7/BUSY + + + + +
8/NO ANSWER + + + + +
9/RESERVED
10/CONNECT 2400 + + + + + + +
11/RINGING + + +
12/VOICE + +
13/CONNECT 9600 + + + + + + +
18/CONNECT 4800 + + + + + + +
20/CONNECT 7200 + + + + + + +
21/CONNECT 12000 + + + + + + +
25/CONNECT 14400 + + + + + + +
Functions
Adaptive Dialing + + + + +
+
Wait for 2nd Dial Tone (W) +
+ + + +
Wait for Answer (@) + + + +
+
Fast Dial + + + +
NOTE: Use &A0 or &A1 to disable/enable
the following ARQ result codes. The
default is &A1, ARQ codes (messages 14
to 19) enabled.
14/CONNECT /ARQ (only when modem is
set to X0)
15/CONNECT 1200/ARQ
16/CONNECT 2400/ARQ
17/CONNECT 9600/ARQ
C-8 Command Summary
COURIER HIGH SPEED MODEMS
19/CONNECT 4800/ARQ
Use &A2 to add HST or V.32 modulation
indicators, as well as ARQ and non-ARQ
status, to the result codes.
Use &A3 to add error control protocol
indicators (LAPM, HST, MNP, SYNC, or
NONE) and data compression type (V42BIS
or MNP5) to the result codes.
Z Software reset to NVRAM settings if DIP
switch 10 is UP, to factory settings if
DIP switch 10 is DOWN. Also initiates
new settings of DIP switches 2-5, 7 and
9.
+++ Escape code, preceded and followed by a
guard time of at least one second of no
data transmission. The modem responds
to +++ by returning to Command mode and
doing the following:
DIP switch 9 UP (OFF, Factory setting):
Hangs up and sends NO CARRIER result
code
DIP switch 9 DOWN (ON): Retains phone
line connection and sends OK result code
> Repeat the command continuously until
canceled by pressing <any key>. If used
in a Dial string, automated redialing
terminates after ten attempts.
/ (Slash) Pause 125 milliseconds.
$ Help Basic command summary request.
&$ Help Extended command summary request.
D$ Help Dial command summary request.
S$ Help S-Register summary request.
Command Summary C-9
COURIER HIGH SPEED MODEMS
<Ctrl>-S Stop/restart display of Help
screens.
<Ctrl>-C Cancel display of Help screens.
or
<Ctrl>-K
AMPERSAND COMMAND SET
&An Enable/disable additional result code
subsets. See the X command in the
previous section.
&A0 ARQ result codes disabled.
&A1 ARQ result codes enabled.
Default.
&A2 Additional HST or V32 modulation
indicator.
&A3 Additional error control indicator
(LAPM, HST, MNP, SYNC, or NONE) and
data compression type (V42BIS or
MNP5).
C-10 Command Summary
COURIER HIGH SPEED MODEMS
&Bn Data Rate, terminal-to-modem (DTE/DCE).
&B0 DTE/DCE rate switches to follow
connection rate (Default).
&B1 DTE/DCE rate remains fixed at the
DTE setting. Allowable rates are
38.4K, 19.2K, 9600, 4800, 2400,
1200, 300 bps.
&B2 Shift to the user-defined fixed,
higher DTE rate for ARQ calls,
follow the connection rate for non-
ARQ calls. Answer mode only.
&Cn Carrier Detect (CD) signal, modem-to-
DTE. DIP switch 6 is factory set so
that the modem controls CD and the
override is disabled.
&C0 CD override (CD always ON).
&C1 Modem sends CD signal when it
connects with another modem, drops
CD on disconnect.
&Dn Data Terminal Ready (DTR) signal, DTE-
to-modem. DIP switch 1 is factory set
for normal DTR operations and the
override is disabled.
&D0 DTR override (DTR always ON).
&D1 Reserved.
&D2 Terminal must send DTR for modem to
accept commands. Dropping DTR
terminates a call.
&F Load factory (ROM) settings into random
access memory (RAM).
Command Summary C-11
COURIER HIGH SPEED MODEMS
&Gn Guard tone as part of answer sequence,
for 2400/1200 bps calls from overseas.
&G0 No guard tone, U.S., Canada
(Default).
&G1 550 Hz guard tone, some European
countries.
&G2 1800 Hz guard tone, U.K., some
Commonwealth countries. Requires B0
setting.
C-12 Command Summary
COURIER HIGH SPEED MODEMS
&Hn Transmit Data flow control.
&H0 Flow control disabled (Default).
&H1 Hardware (Clear to Send) flow
control.
&H2 Software (XON/XOFF) flow control.
&H3 Hardware and software flow control.
&In Received Data software flow control.
&I0 Flow control disabled (Default).
&I1 XON/XOFF to local modem and remote
computer.
&I2 XON/XOFF to local modem only.
&I3 Host mode, Hewlett Packard protocol.
&I4 Terminal mode, Hewlett Packard
protocol.
&I5 Same as &I2 in ARQ mode. In non-ARQ
mode, XON/XOFF to remote modem for
link flow control.
&Kn Data compression.
&K0 Disabled.
&K1 Auto enable/disable (Default).
Disabled if modem is set to &B0 and
DTE rate switches to match link
rate.
&K2 Enabled regardless of &Bn setting.
&K3 Selective data compressionêMNP Level
5 disabled.
Command Summary C-13
COURIER HIGH SPEED MODEMS
&Ln Normal/Leased phone line.
&L0 Normal phone line (Default).
&L1 Leased line; enables the modem to
reconnect if disconnected.
&Mn Error Control (ARQ) and Synchronous
Operation.
&M0 Normal asynchronous mode, error
control disabled.
&M1 Synchronous mode, error control
disabled.
&M2 Reserved.
&M3 Reserved.
&M4 Normal/ARQ asynchronous mode
(Default). Normal connection if ARQ
connection cannot be made.
&M5 ARQ asynchronous mode. Modem hangs
up if ARQ connection cannot be made.
&Nn Link Rate (DCE/DCE) variable or fixed.
With fixed link rate, modem hangs up if
called or calling modem is operating at
a different rate.
&N0 Variable link operations (Default).
Modem negotiates highest possible
link rate with remote modem.
&N1 300 bps.
&N2 1200 bps.
&N3 2400 bps.
&N4 4800 bps.
C-14 Command Summary
COURIER HIGH SPEED MODEMS
&N5 7200 bps.
&N6 9600 bps.
&N7 12K bps
&N8 14.4K bps
&Pn Pulse dialing make/break ratio.
&P0 U.S./Canada make/break ratio
(Default).
&P1 U.K./some Commonwealth countries
make/break ratio.
&Rn Received Data hardware (RTS) flow
control.
&R0 Delay before modem responds to DTE's
RTS signal with CTS signal. Delay
is set in Register S26.
&R1 Ignore RTS (Default).
&R2 Received data sent to DTE only when
RTS is high; used only if DTE
supports RTS signaling.
&Sn Data Set Ready (DSR) operations.
&S0 DSR override, always ON (Default).
&S1 Modem sends DTE a DSR signal when it
senses a modem tone on the phone
line.
&S2 On loss of carrier, modem sends DTE
a pulsed DSR signal with Clear to
Send (CTS) following Carrier Detect
(CD).
Command Summary C-15
COURIER HIGH SPEED MODEMS
&S3 This is the same as &S2, but without
CTS following CD.
&Tn Modem testing.
&T0 End test.
&T1 Initiate Analog Loopback (AL)
testing.
&T2 Reserved.
&T3 Initiate Local Digital Loopback
(LDL) testing.
&T4 Grant Remote Digital Loopback (RDL).
&T5 Prohibit RDL.
&T6 Initiate RDL testing.
&T7 Initiate RDL with self-test and
error correction.
&T8 Initiate AL with self-test and error
correction.
&W Write current settings to nonvolatile
random access memory (NVRAM).
&Xn Synchronous Timing Source. This
specifies whether the modem or DTE
generates the timing signals for the
Transmit clock during a synchronous
call.
&X0 Modem's Transmit clock is the source
(Default).
&X1 DTE is the source.
&X2 Modem's Receiver clock is the
source; valid only in V.32 bis mode
C-16 Command Summary
COURIER HIGH SPEED MODEMS
or for 2400/1200-bps connections in
HST mode.
&Yn Break handling. Destructive Breaks
clear the buffer; expedited Breaks are
sent immediately to the remote system.
Under data compression, destructive
Breaks cause both modems to reset their
compression tables.
&Y0 Destructive, don't send Break.
&Y1 Destructive, expedited (Default).
&Y2 Nondestructive, expedited.
&Y3 Nondestructive, unexpedited; modem
sends Break in sequence with data
received from DTE.
&Zn = s Write the following Dial string (s)
to NVRAM at position n
(n = 0-3).
Command Summary C-17
COURIER HIGH SPEED MODEMS
&Zn? Display the phone number stored in NVRAM
at position n
(n = 0-3).
PERCENT COMMAND SET
%Rn Rack Controller Unit (RCU) access. For
use with USRobotics Total Control Modem
Management Systems.
%R0 Normal operations, RCU access
disabled (Default).
%R1 RCU access enabled.
%T Touch-Tone Recognition mode enabled.
C-18 Command Summary
COURIER HIGH SPEED MODEMS
APPENDIX D. PROBLEMS AND SOLUTIONS
You may occasionally encounter one of
the problems listed here. They are
divided into two categories: before and
during the exchange of user information
over the data link.
Before Establishment of the Data Link
Your modem . . .
Doesn't answer the phone or go off hook to
dial a number
Review the Settings Supplement that came
with the modem or your communications
software manual to see what Data
Terminal Ready (DTR) operations your
software requires. Then check to see if
DIP switch 1 is set correctly. Also,
check to make sure your terminal or
computer is sending a DTR signal via the
RS-232 interface.
Doesn't respond OK when you type AT <Enter>
1. Make sure you're typing in either
upper case or lower case letters, not
a combination, and that you press the
Enter key.
2. If you're using a computer, make sure
it is in Terminal Mode. This is a
communications software function.
See Testing the Modem in Chapter 2.
3. Check to see that your terminal or
software is set to the correct bit
Problems and Solutions D-1
COURIER HIGH SPEED MODEMS
rate and word length (7 bits with or
without a parity bit, or 8 bits and
no parity). If you're using a
computer, make sure your software is
set to the correct communications
port.
4. Check that DIP switch 8 is DOWN, for
command set recognition. If the
switch is UP, power off the modem,
set the switch DOWN, and power on the
modem again. Try typing AT <Enter>
again.
5. Check that DIP switch 3 is DOWN, for
result code display, and that DIP
switch 2 is UP, for verbal result
codes. If not, change the switch(es)
and type ATZ <Enter>. Or type
whichever of these commands is
needed:
D-2 Problems and Solutions
COURIER HIGH SPEED MODEMS
ATQ0 <Enter> (to enable the message)
ATV1 <Enter> (to display a verbal
message)
6. Review the Settings Supplement that
came with the modem or your communi-
cations software manual to see what
Carrier Detect (CD) operations your
software requires. Then check to see
if DIP switch 6 is set correctly.
7. A rare condition is that your
terminal or computer reverses the
send/receive functions at the RS-232
interface. See Appendix B-1,
Appendix B-3, Quad switch, and your
equipment documentation.
Displays double characters
Both your modem's and software's local
echo are characters on. You can turn
your software's local echo off. Or turn
the modem's echo off by either resetting
DIP switch 4 and sending the modem the
ATZ command, or by sending the modem the
ATE0 command.
Your computer . . .
Reacts as though a data link has been
established, but no call has been received
DIP switch 6 is set DOWN at the factory
for Carrier Detect (CD) override, but
your system may require that the
override be turned OFF.
Review your terminal's manual, the
Settings Supplement that came with the
modem or your communications software
manual to see what CD operations are
Problems and Solutions D-3
COURIER HIGH SPEED MODEMS
required. Then check to see if DIP
switch 6 is set correctly.
When the modem is in Answer mode, acts if a
Carriage Return has been entered, but
nothing has been typed at the keyboard
Your software may be misreading signals
from the modem as it automatically sends
a Carriage Return and a Line Feed before
and after the RING and CONNECT messages.
Sending the Quiet Mode command, ATQ1
<Enter>, should solve the problem.
D-4 Problems and Solutions
COURIER HIGH SPEED MODEMS
Both modems . . .
Exchange carrier signals, but fail to
establish a communications link
1. Asynchronous operations: Check to
make sure the proper bit rate, word
length, parity and number of Stop
bits have been selected. Synchronous
operations: review the link
instructions in Chapter 7. If you've
set the modem to the correct
configuration, the problem may be
with the synchronous adapter or with
the system you're trying to call.
2. Check to see that your modem is at
the correct Bn setting to connect
with either an HST modem (B1 setting)
or V.32 modem (B0 setting). Type
ATI4 for a display of the Courier's
current settings and, if necessary,
send the modem the correct setting.
3. If your modem is attempting to answer
a V.32 call, you may need to lengthen
the extra V.32 answer tones. See S28
in Appendix B-5.
4. Make sure the modem at the other end
of the line is USR-HST compatible at
14.4K or 9600 bps, V.32-compatible at
9600 bps, V.22 bis-compatible at 2400
bps, Bell 212A-compatible at 1200
bps, or Bell 103-compatible at 300
bps. These are the common signaling
standards for full duplex dial-up
network transmission in the U.S.
5. If none of the above corrects the
problem, it's likely that the quality
of the phone connection is poor and
that the other modem is missing the
Problems and Solutions D-5
COURIER HIGH SPEED MODEMS
signals your modem is transmitting.
The variable quality of phone line
connections may be due to any number
of conditions in the phone service's
equipment or the current environment.
Try several calls, and if you still
can't get through, try calling
another modem. If the second modem
accepts your call, the problem may
lie with the modem you first tried to
call.
During Data Transfer
Your screen displays . . .
Only brackets
Check to make sure that both modems are
set to the same bit rate, word length,
parity and number of Stop bits. If the
settings
D-6 Problems and Solutions
COURIER HIGH SPEED MODEMS
are correct, the problem may be with the
phone line. Try the following measures:
1. Try placing the call again. The
phone company routes even local calls
differently each time you call.
2. Try calling a different modem to see
if the problem persists. The problem
may be with the modem you first tried
to call.
Random or garbage characters
Check to make sure that both modems are
set to the same bit rate, word length,
parity, and number of Stop bits.
If the modem is set to a fixed DTE rate
(&B1) and your software is fixed at
19.2K or 38.4K bps, the reason may be
one of the following:
1. Your computer may not support the
high rate. If this is the case, fix
your software rate at 9600 bps and
disable high-speed V.32 bis
modulation: ATS34=3 or ATS34 .0=1
.1=1.
2. If you use memory-resident programs
(TSRs), they may be interfering. Try
disabling them before you run your
communications software. The same is
true of disk-caching programs.
3. Check to see that your software and
the modem are set for the same kind
of flow control, either hardware or
software. Some communications
programs also require that you dis-
able the kind you are not using.
Problems and Solutions D-7
COURIER HIGH SPEED MODEMS
Double characters
Your modem's online local echo is on and
the remote modem is also echoing. The
only way to correct this is to bring the
modem back to Command mode (wait one
second without transmitting data, type
+++, wait another second). Then type
the command to turn off your online echo
(ATF1 <Enter>).
If DIP switch 9 is UP (factory setting),
the modem hangs up when it returns to
Command mode, and you'll have to call
again. If DIP switch 9 is DOWN, the
modem maintains its connection. You can
return it back online by typing ATO
<Enter>.
D-8 Problems and Solutions
COURIER HIGH SPEED MODEMS
IF YOU STILL HAVE PROBLEMS
The problems described above are by far
the most common ones that users
encounter. If the suggestions we've
given don't clear up your difficulties,
try the following:
1. Review the manual carefully to see if
you've missed something.
2. Call or visit your dealer. Chances
are your dealer will be able to give
you the assistance you need. This is
much more efficient and time-saving
than returning the modem to
USRobotics.
3. If your dealer can't clear up your
difficulties, call the USRobotics
Technical Support Department at
800/982-5151. Our Service
Representatives will be happy to give
you assistance over the phone Monday
through Friday from 8:30 a.m. to 5
p.m. (Central Time Zone).
4. If necessary, the Service
Representative you talk to may give
you a Return Materials Authorization
(RMA) number. Modems without an RMA
number will not be accepted.
5. If you do return the modem to us,
please use the following procedures.
a. Ship the unit, postage paid, in
its original container. If the
original container is not
available, pack the modem carefully
in a strong box of corrugated
Problems and Solutions D-9
COURIER HIGH SPEED MODEMS
cardboard with plenty of packing
material.
b. Be sure to include your RMA
number inside the package, along
with your name and address. Put
your return address and your RMA
number on the shipping label as
well.
c. Ship the well-packed modem to
the following address.
Technical Support Department
U.S. Robotics, Inc.
8100 North McCormick Boulevard
Skokie, Illinois 60076
d. Please note that USRobotics
will not accept packages sent COD,
so be sure to send the modem
postage paid.
e. USRobotics will repair your
modem and return it to you via
United Parcel Service.
D-10 Problems and Solutions
COURIER HIGH SPEED MODEMS
APPENDIX E. ADDITIONAL OPERATIONS
CONTENTS
Voice/Data
High Speed/Low Speed Protocol
Dedicated and Leased Line
Operations
Hewlett Packard 3000 Installations
MI/MIC Operations
Additional Operations E-1
COURIER HIGH SPEED MODEMS
VOICE/DATA
The voice/data switch is located on the
modem's front panel. While the switch's
primary function is to toggle back and
forth between voice and data
communications, this new feature also
allows you to perform other functions at
the touch of a switch. Set Register S32
for any one of the functions, and change
that function any time you wish.
NOTE: Use the voice/data switch when
the modem is in Command mode (offline).
If you press the switch while the modem
is online, the modem hangs up and
returns a NO CARRIER result code.
VOICE/DATA OPERATIONSêS32=1, S32=2 OR AT
COMMANDS
When you assemble the Courier, 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 switch between the phone and modem
during a call.
Users of Courier modems have always been
able to phone and make arrangements with
another user before turning control of
the call over to the modems. However,
it was difficult to switch from data to
voice. Now, if the remote modem has
handset exclusion, you can change from
voice to data and back again, with or
without issuing a command.
Handset exclusion means that if the
modem is using the phone line, your
E-2 Additional Operations
COURIER HIGH SPEED MODEMS
phone (handset) is automatically dis-
connected. However, if you keep the
handset off hook, once you hang up the
modem the handset takes over the phone
line and you can use voice
communications again. If the remote
user does not have handset exclusion,
you may not be able to switch back to
voice mode successfully once you have
switched to data mode.
The following instructions begin with
toggling voice/data communications with
the switch. These are followed by
instructions for doing the same thing
with AT commands. Keep in mind that you
can use the switch and, if the remote
user does not have a switch, he or she
can follow the instructions for using
the appropriate AT command.
Additional Operations E-3
COURIER HIGH SPEED MODEMS
Voice/Data SwitchêS32=1, S32=2
1. Phone the other user to establish the
bit rate, parity, word length and
number of Stop bits the other
person's modem accepts. (Both modems
should be offline, in Command mode.)
You and the other user must also
agree on which modem will go off hook
in Originate mode and which in Answer
mode. The Courier is factory set to
go off hook in Originate mode, S32=1.
The Answer modem should have S32 set
to 2.
NOTE: Either party's device can be
the originate or answer modem: it
doesn't matter who made the phone
call. But one modem must first enter
Originate mode and the other then
enter Answer mode.
2. Without hanging up the phone, press
the voice/data switch.
(If S32 is set to 2, Answer mode,
press the voice/data switch
immediately after the remote user
forces the remote modem off hook in
Originate mode.)
3. The other party should force the
remote modem off hook in Answer mode
by pressing the switch.
(If yours is the Answer modem
(S32=2), the other party should press
the voice/data switch immediately
before you do so.)
4. If the remote modem has handset
exclusion, the remote user should
E-4 Additional Operations
COURIER HIGH SPEED MODEMS
also keep the phone off hook in order
to switch back to voice later. If
the remote modem doesn't have handset
exclusion, you can try to switch back
to voice later. Or, you both can
hang up your phones as soon as the
modems go off hook.
Software CommandsêATD, ATA
If your voice/data switch is set for a
function other than voice/data
operations and you don't wish to change
it, use commands.
1. Call the other user to establish the
bit rate, parity, word length and
number of Stop bits the other
person's modem accepts. Determine
which modem will originate and which
will answer.
2. If you are to originate the
connection, type the following
command:
ATD <Enter>
NOTE: Be sure the modem is not set
to X2, X4, X6 or X7, or it will
return the NO DIAL TONE result code
and hang up.
3. The other party must then have the
remote modem go off hook in Answer
mode. The following command is used
to do this:
ATA <Enter>
4. If the remote modem also has handset
exclusion, leave both phones off hook
Additional Operations E-5
COURIER HIGH SPEED MODEMS
in case you wish to switch back again
to voice after your data transfer.
If the remote modem doesn't have
handset exclusion, switching back to
voice may not be successful. If you
don't want to switch back to voice
later, hang up both phones as soon as
the modems go off hook.
ALLOWABLE VOICE/DATA SWITCH FUNCTIONS
Use Register S32 to set the voice/data
switch for the function you desire. S32
is not bit-mapped. The value for each
option is absolute and exclusive. The
default is S32=1êthe switch forces the
modem off hook in Originate mode. You
may set the switch to any one of the
following functions:
S32 Related
Value Voice/Data
Switch Function Command
0 Disabled ê
1 Voice/Data+Originate Mode
(Default) ATD
(Chapt
er 7,
Appendix C)
2 Voice/Data+Answer Mode ATA
(Appen
dix C)
3 Redial Last Number ATDL
(Chapter 6)
4 Dial Number Stored at position
0ATDS0
(Chapt
er 6)
5 Auto Answer On/Off Toggle A
TS0=0 or 1
E-6 Additional Operations
COURIER HIGH SPEED MODEMS
(Chapt
er 6)
6 Reset Modem ATZ
(Chapter 5)
7 Initiate Remote Digital
Loopback AT&T6, S16=8
(Appen
dix F)
Additional Operations E-7
COURIER HIGH SPEED MODEMS
HIGH SPEED/LOW SPEED PROTOCOL
OVERVIEW
This appendix explains how an answering
Courier modem switches its link rate to
match the rate of a calling modem. It
may be of help also to those users who
want to try programming their computers
to switch bit rates to match the
Courier's connection rate. The material
here applies only when the modem is set
for variable rates at both the DTE
(computer) and link interfaces, &B0 and
&N0, respectively.
In both Originate and Answer modes, if
the link rate is set to &N0, the Courier
negotiates with the remote modem to
connect at the highest possible rate.
In addition, if the modem is set to
Extended or Advanced result codes (X1 or
higher) it signals the DTE with one of
the following result codes or the
optional result codes selected with the
&An command.
CONNECT (300 bps)
CONNECT 1200 (1200 bps)
CONNECT 2400 (2400 bps)
CONNECT 4800 (4800 bps)
CONNECT 9600 (9600 bps)
The modem sends the result code at its
previous rate. Then it switches to the
new connection rate.
If your computer doesn't switch rates
and you want to program it to do so, use
the example on the next page as a guide.
It demonstrates the occurrence of the
CONNECT codes in the connection
E-8 Additional Operations
COURIER HIGH SPEED MODEMS
sequence, so that recognition of the
codes can be used to switch the
computer. The example uses a sequence
of incoming calls, but the codes apply
to Originate mode connections as well.
The example assumes the following
settings:
Software: Initially 9600 or 19.2K,
or 38.4K bps, allowing the
following range of link rates:
9600/4800/2400/1200/300/110 bps
Modem: X1 or higher (rate-
specific CONNECT codes) &B0
(variable DTE rate) &N0
(variable link rate)
NOTE: The HST-mode link rate of 14.4K
bps is not included because this link
rate requires a fixed DTE rate of 19.2K
or 38.4K bps, that is, a modem setting
of &B1.
Example
Modem DTE/DCE
Action Response Rate
1. Power on.
9600
2. 300-bps call comes in. RING
9600
CONNECT
9600
3. Data link is established.
300
Data transfer takes place.
4. Data session is over. NO CARRIER
300
Call is ended; loss of
Additional Operations E-9
COURIER HIGH SPEED MODEMS
carrier.
5. 2400-bps call comes in. RING
300
CONNECT
2400 300
6. Data link is established.
2400
Data transfer takes place.
7. Data session is over. NO CARRIER
2400
Call is ended; loss of
carrier.
8. 9600-bps call comes in. RING
2400
CONNECT
9600 2400
9. Data link is established.
9600
Data transfer takes place.
10. Data session is
over. NO CARRIER 9600
Call is ended; loss of
carrier.
E-10 Additional Operations
COURIER HIGH SPEED MODEMS
Explanation
1. The modem is powered on and is
operating at 9600 bps. If the
software is then set to 19.2K bps and
an AT command sent, the DTE/DCE rate
would be 19.2K bps.
2. A 300-bps modem calls. The Courier
senses the incoming signal and sends
the messages RING and CONNECT to the
computer. These messages are sent at
9600 (or 19.2K) bps, the current
rate.
3. Since the Courier responds CONNECT,
rather than CONNECT 1200, 2400, or
9600, the computer switches to 300
bps. The modem automatically shifts
to 300 bps to accept the data from
the incoming call.
4. The 300-bps data session is
terminated; the modem sends the
computer the message NO CARRIER at
300 bps.
5. A 2400-bps call comes in. The modem
responds RING and CONNECT 2400.
These message are sent at the current
bit rate of 300 bps.
6. The computer, receiving the CONNECT
2400 message, adjusts accordingly to
the higher bit rate. The modem also
shifts to 2400 bps.
7. The 2400-bps data session is
terminated; the modem sends the
computer the message NO CARRIER at
2400 bps.
Additional Operations E-11
COURIER HIGH SPEED MODEMS
8. A 9600-bps call comes in. The modem
responds RING and CONNECT 9600.
These messages are sent to the
computer at the current bit rate of
2400 bps.
9. The computer, receiving the CONNECT
9600 message, adjusts accordingly to
the higher bit rate. The modem also
shifts to 9600 bps.
10. The 9600-bps data session is
terminated; the modem sends the
message NO CARRIER at 9600 bps.
Keep in mind that whether or not your
computer adjusts to these rate changes,
the Courier automatically shifts
connection rates if it is set to &N0.
E-12 Additional Operations
COURIER HIGH SPEED MODEMS
DEDICATED AND LEASED LINE OPERATIONS
The following operations apply in
installations where the modem's phone
line is not part of a public-access
switched telephone network. Instead,
the modem is connected to a special
user-installed telephone line or a line
that is leased from the telephone
company. These lines are often referred
to as dedicated (to a pair of modems) or
private lines.
In both types of installation there is a
continuous point-to-point connection
between two modems. No dialing of phone
numbers is required. The modems may be
in either Smart or Dumb mode (determined
by the position of DIP switch 8).
The User-Installed or Leased Telephone Line
User-installed lines are most commonly
2-wire lines, similar to the 2-wire
lines that connect residential phones to
the public switched network.
If you are leasing a line from the
telephone company, request a 2-wire
line, the type of line the modem is
designed to work with. If the telephone
company only makes a 4-wire line
available, you'll need a 4-wire to 2-
wire converter at each end of the
connection. If the phone company does
not install the converters, you will
have to supply them.
For optimal operations, we recommend
that the physical length of these lines
not exceed 5 miles.
Additional Operations E-13
COURIER HIGH SPEED MODEMS
Setting the Modem
If the Courier is set to &L1, as
described in what follows, and the
remote AT-compatible modem has a
comparable setting, they automatically
connect when they are powered on. They
also reconnect, without any operator
intervention, if a disturbance on the
line is severe enough to break the
connection.
Set the modem as follows:
1. Set your terminal or communications
software to the rate at which you
want the modems to communicate. For
example, use a terminal/software
setting of 19.2K bps and, if both
modems have the capability, they will
connect at 14.4K bps. The following
instructions assume that you are
familiar with
E-14 Additional Operations
COURIER HIGH SPEED MODEMS
the guidelines on using the &B and &H
commands (Chapter 3 or, in more
detail, Chapter 4) and the &W command
(Chapter 5).
2. Send the modem the following command:
AT &B1 &S2 &H1 &L1 &W <Enter>
&B1 fixes the modem's computer
interface rate at 19.2K bps. &S2
causes the modem to send a Clear to
Send (CTS) signal only after it sends
the Carrier Detect (CD) signal, that
is, only after it connects with the
remote modem. (See the note that
follows.) &H1 enables hardware (CTS)
flow control.
&L1 forces the modems off hook at
power on and enables them to re-
establish the connection should it be
broken. &W writes the settings to
nonvolatile memory (NVRAM) as power-
on defaults.
NOTE: We recommend using the &S2
setting, to delay CTS until after the
connection is made, as a precaution.
If the modems are in the process of
connecting or reconnecting, the
Courier interprets any keyboard data
entry, including an accidental key
stroke, as a key-press abort, and
hangs up. Delaying CTS until after
carrier detection prevents this from
happening, for example, if you are
typing data to the remote modem when
the modems momentarily disconnect and
begin to reconnect. However, you
have to set the modem for hardware
flow control, &H1.
Additional Operations E-15
COURIER HIGH SPEED MODEMS
If your software or machine does not
support Clear to Send (CTS), don't
inlcude &S2 and &H1 in the command
string suggested above. Follow the
Transmit Data flow control (&H)
guidelines in Chapter 4. But keep in
mind that if the modems fail to
connect or reconnect, the reason
could be a key-press abort.
3. Set the modem to load NVRAM settings
at power-on, DIP switch 10 UP. It
does not matter if the modem is in
Dumb or Smart mode (DIP switch 8).
4. Decide which modem is to be the
calling modem and which the answering
modem. Set the answering modem to
Auto Answer, DIP switch 5 UP, and the
calling modem to Auto Answer
suppressed, DIP switch 5 DOWN.
5. Power off and power on the modems.
This initiates the new DIP switch
settings and loads the power-on
defaults, including &L1. The modems
go off hook and establish the
connection.
NOTE: If the modems cannot restore the
connection and you could not set the
modem to &S2, the reason could be a key-
press abort. If the problem persists,
however, you may need to call your
telephone company to have them check
your line.
E-16 Additional Operations
COURIER HIGH SPEED MODEMS
HEWLETT PACKARD INSTALLATIONS
During error control connections, the
Courier recognizes the ASCII ENQ/ACK
characters exchanged between many
Hewlett Packard host computers and their
terminals. The HP host sends the
terminal an ENQ character at predefined
intervals, and sends no more data until
the terminal responds with an ACK
character.
Courier modems manage this ENQ/ACK
protocol so that communication is
speeded up, thereby enabling HP
terminals to achieve high speeds on
dial-up lines. Special flow control
settings, using the &I command, are
required for HP users. These settings
apply to ARQ and non-ARQ connections and
to Courier modems set to either B0 or
B1. Disregard other Courier flow
control commands.
Set the Courier to Host mode if it is
attached to the host computer, or to
Terminal mode if it is attached to a
terminal, as follows:
Host mode AT&I3 <Enter>
Terminal mode AT&I4 <Enter>
Additional Operations E-17
COURIER HIGH SPEED MODEMS
MI/MIC OPERATIONS
DESCRIPTION
Mode Indicate/Mode Indicate Common
(MI/MIC) closure is required by some
installations whose existing hardware
does the dialing. The modems do not
Auto Dial.
In these situations, the modem must be
forced off hook in Originate mode. This
is done by shorting (closing) two of the
pins (not Tip and Ring) in the phone
connector. The modem is then ready to
go online and accept data when it
connects with the number dialed by the
system equipment.
Courier modems are shipped with MI/MIC
disabled, that is, for normal use. To
set the modems for MI/MIC closure,
enable bit 5 of Register S34: ATS34=32
or ATS34 .5=1. We recommend that you
write that setting to NVRAM as a power-
on default.
Once you've set Register S34, have the
system force the modem off hook by
closing the MI/MIC leads in the phone
line connector. The modem's OH (Off
Hook) status light, or LED, goes on when
the modem goes off hook.
TROUBLESHOOTING
You may find that the modem does not
respond to MI/MIC closure, which you can
monitor by observing the LED. Or the
modem may fail to go back on hook when
the DTE drops the Data Terminal Ready
(DTR) signal. The probable reason for
E-18 Additional Operations
COURIER HIGH SPEED MODEMS
either of these conditions is that your
phone equipment reverses MI/MIC
polarity.
It's possible to solve this problem by
reversing the modem's MI/MIC wiring.
You'll have to dismantle the modem case
and reset two switches on the printed
circuit board, as follows.
1. Power off the modem and disconnect
all of its cables.
2. Turn the modem upside down. Remove
the two square vinyl feet near the
back of the case, on either side of
the bottom label's DIP switch
diagram. Be careful to put the vinyl
feet aside, upside down, where they
won't become stuck to another object.
3. Remove the two Phillips screws.
Raise the back end of the case bottom
until it is at about a 60ø angle;
lift it away from inside the front of
the modem. Put the case bottom
aside.
4. Locate the Voice/Data switch and
Volume Control at the front of the
modem. Lift up and remove the modem
(printed circuit board), carefully
easing the Voice/Data switch out of
its opening in the front panel.
5. Turn the modem rightside up and
locate jumper switches J6 and J8,
near the power-adaptor socket. Use
Figure E-1 as a guide.
Additional Operations E-19
COURIER HIGH SPEED MODEMS
Figure E-1êCourier Modem Board
6. The jumpers are black shunts that
cover two out of three upright metal
contacts. As shown in the figure,
the modem is shipped with the jumpers
over the two contacts on each switch
that are closest to the front panel.
The third contact on each switch is
exposed.
Lift off the jumpers from J6 and J8.
Reverse the positions shown in Figure
E-5.1. That is, on each switch,
cover the contact closest to the back
of the modem and the contact at the
center. Make sure the jumpers cover
two contacts on each switch, or
you'll disable the MI/MIC function.
7. Replace the modem in the case top:
ease the Voice/Data switch into the
opening in the front panel; set the
Volume Control on its semicircular
rack; make sure the back of the board
rests on the locator pins at the rear
(from which you removed the screws).
E-20 Additional Operations
COURIER HIGH SPEED MODEMS
8. Reconnect the modem's RS-232, power
and phone cables, in that order. Be
sure the phone cable is plugged into
the jack closest to the center of the
modemêthe jack represented by the
wall jack icon on the case bottom
label.
CAUTION: When you power on the modem
there will be potential hazardous
voltage, particularly near the phone
jacks. Do not touch the board when
the power is on.
9. Power on the modem. Try MI/MIC
closure again. Check to see that the
Off Hook (OH) status light goes on.
If you dialed a number, listen for an
answer tone from the remote modem.
Then drop the DTR signal. The modem
should go on hook and the OH status
light should go off.
10. If closure is not working properly,
review the steps in this appendix.
Be sure the jumper switches are in
the reverse position of those in
Figure E-5.1. If you still have
problems, there may be a problem with
the phone cable. Or there may be a
problem with your hardware.
11. When the equipment is working
correctly, replace the bottom of the
modem case. Ease the two nibs near
the front corners into their openings
in the front of the case top, and
snap the back of the case bottom into
place. Replace the two screws and
the two vinyl feet.
Additional Operations E-21
COURIER HIGH SPEED MODEMS
APPENDIX F. MODEM TESTING
Testing is available with the &T command
or Register S16. All loopback testing
conforms to CCITT Recommendation, V.54.
Earlier USRobotics high speed modems,
however, did not perform the &T test
repertoire.
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.
TESTING WITH &T
The tests supported through the &T
command include analog loopback, digital
loopback and remote digital loopback.
Users can key in their own data during
testing, or use the modem's internal
test pattern and error detector.
In all cases, disable error control
before testing. If the modem is
detecting errors and retransmitting the
affected data, your results will be
invalid.
During testing, the MR status light
flashes.
Ending a Testê&T0, S18
Issuing the &T0 command terminates 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
Modem Testing F-1
COURIER HIGH SPEED MODEMS
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 defaults.
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. You cannot store
a value for S18 in nonvolatile memory:
its power-on and reset default is always
zero.
F-2 Modem Testing
COURIER HIGH SPEED MODEMS
ANALOG LOOPBACKê&T1, &T8
This test checks the operation of the
modem's transmitter and receiver. Data
flow is shown in Figure F-1.
Figure F-1. Data Flow During Analog Loopback
There are two analog loopback options.
The first, &T1, involves your typing
data that you can verify at your screen.
The second option, &T8, is an internal
self-test that does not involve the
keyboard or screen. It isolates the
modem from the computer interface to
give you a more specific result.
NOTE: HST or Dual Standard modems must
be tested at 2400 bps or lower to avoid
asymmetrical modulation at higher
speeds.
&T1
1. If you are testing an HST or Dual
Standard modem, set your terminal or
software to 2400 bps.
2. The modem must be in Command mode.
If you wish, set Register S18 as a
test timer, as explained earlier.
Modem Testing F-3
COURIER HIGH SPEED MODEMS
3. Send the modem the following command.
AT &M0 &T1 <Enter>
The modem disables error control,
enters analog loopback (AL) mode, and
sends a CONNECT message. The MR
status light flashes.
4. Type recognizable data so that you
can verify it when it is looped back
to the screen.
5. End the test. If you set S18, the
modem automatically stops the test at
the timeout, exits AL mode and
responds OK.
F-4 Modem Testing
COURIER HIGH SPEED MODEMS
If you didn't set Register S18, wait
one second and type +++ to bring the
modem back to Command mode. If DIP
switch 9 is UP, the modem also hangs
up and ends the test.
If DIP switch 9 is DOWN, type AT&T0
to end the test. 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 the modem
sends an ERROR message, you have
issued an invalid command.
6. If there were no errors, reset the
modem to &M4, for error control,
unless you've issued the ATZ reset
command.
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 characters.
&T8
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
Modem Testing F-5
COURIER HIGH SPEED MODEMS
no errors but your problem continues, it
may be at the computer interface.
1. If you are testing an HST or Dual
Standard modem, set your terminal or
software to 2400 bps.
2. The modem must be in Command mode.
If you wish, set Register S18 as a
test timer, as explained earlier.
3. Send the modem the following command:
AT &M0 &T8 <Enter>
The modem disables error control and
enters AL mode. The MR status light
flashes. The modem sends its
internal test pattern to the trans-
mitter, and loops the pattern back to
the receiver. You will not see any
data on your screen.
4. 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.
The modem hangs up and 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
command.
5. If there were no errors, reset the
modem to &M4 for error control unless
you issued the ATZ command.
F-6 Modem Testing
COURIER HIGH SPEED MODEMS
&T2
This option is reserved.
DIGITAL LOOPBACKê&T3
If your modem has passed the AL test,
this test can help you locate a problem
with a remote modem or the telephone
channel. Figure F-2 shows the data flow
during DL testing.
Figure F-2. Data Flow During Digital Loopback
NOTE: This test requires the modem to
establish a connection and return to
online-command mode in response to the
+++ escape code. DIP switch 9 must be
set DOWN so that the modem does not hang
up on receipt of the escape code. After
you change the switch, issue ATZ to the
modem to initiate the new setting.
As with AL testing, HST and Dual
Standard modems should be tested at 2400
bps or lower,
1. Set the modem to &M0, to disable
error control. HST and Dual
Standard modems should be set to 2400
Modem Testing F-7
COURIER HIGH SPEED MODEMS
bps or lower to avoid asymmetrical
modulation at higher speeds.
Establish a connection with the
remote modem.
2. Bring the modem back to Command mode
with the +++ escape code. Then send
it the AT&T3 command. The modem
enters DL mode and the MR status
light flashes.
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. 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 the modem
sends an ERROR message, you have
issued an invalid command.
5. Reset DIP switch 9 UP if you normally
use the factory default. Reset the
modem to &M4 unless you used the
reset command, ATZ.
&T4, &T5
The &T4 option causes the modem to grant
a remote modem's request for a Remote
Digital Loopback test.
The &T5 option cancels &T4, and the
modem fails to recognize such a request.
This is the default so that your modem
F-8 Modem Testing
COURIER HIGH SPEED MODEMS
isn't subject to another user calling
and tying up your modem without your
permission.
REMOTE DIGITAL LOOPBACKê&T6, &T7
This test, like the local digital
loopback test, verifies the condition of
both modems and the phone link. Data
flow is shown in Figure F-3.
Figure F-3. Data Flow During Remote Digital
Loopback
The request for and granting of Remote
Digital Loopback testing requires that
both modems use CCITT V.22 standard
signaling. The test must be performed
at 2400 bps or lower. If the remote
modem does not have the capability or is
not set to respond, you will get an
ERROR result code.
As with Analog Loopback, there are two
Remote Digital Loopback options. If you
select &T6, you send keyboard data to
the modem and verify it when it is
returned over the phone lines and to
your screen. If you select &T7, the
modem sends its internal test pattern
Modem Testing F-9
COURIER HIGH SPEED MODEMS
and returns an error count to your
screen.
NOTE: Both test options require the
modem to establish a connection and
return to online-command mode in
response to the +++ escape code. DIP
switch 9 must be set DOWN so that the
modem does not hang up on receipt of the
escape code. If necessary, set the
switch DOWN and then issue the ATZ
command to the modem to initiate the new
switch setting.
&T6
1. Set the software to 2400 bps or
lower. 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 and,
if necessary, set the remote modem to
acknowledge the RDL request. For
example, older USRobotics high speed
modems need to be set to S16=8.
2. Bring the Modem back to Command mode
with the +++ escape code. Send it
the AT&T6 command. The modem enters
RDL mode and the MR status light
flashes.
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
F-10 Modem Testing
COURIER HIGH SPEED MODEMS
test when the test timeout is
reached. If you didn't set S18, type
AT&T0 to end the test. 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
loopback testing with your modem, the
problem may also lie with your modem.
5. Reset DIP switch 9 UP unless you
normally set that switch DOWN, and
issue ATZ to the modem to initiate
the new setting. Reset the modem to
&M4 unless you used the reset
command, ATZ.
&T7
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 screen.
You don't need to type anything during
this test. The modem sends only its
final error count to your screen.
1. Set the software to 2400 bps or
lower. Set the modem to &M0. If you
wish, set the S18 timer.
Establish a connection with the
remote modem. If you haven't already
Modem Testing F-11
COURIER HIGH SPEED MODEMS
done so, arrange with the remote user
to cooperate with your testing and,
if necessary, set the remote modem to
acknowledge the RDL request. For
example, older USRobotics high speed
modems need to be set to S16=8.
2. Bring the modem back to Command mode
with the +++ escape code. Then send
it the AT&T7 command. The modem
enters RDL mode and the MR status
light flashes.
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. 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.
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'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.
F-12 Modem Testing
COURIER HIGH SPEED MODEMS
4. Reset DIP switch 9 UP unless you
normally operate with it DOWN. Issue
an ATZ command to initiate the new
switch setting. Reset the modem to
&M4 unless you've sent it the ATZ
reset command.
TESTING WITH REGISTER S16
Register S16 is a bit mapped register
with the following bit functions:
Bit Value Function
0 1 Analog Loopback (AL)
1 2