5.1 Introduction
Your MT2834MR has intelligent features beyond those of the AT
command set (described in Chapter 3 of this manual). This chapter
covers these high performance features and commands which provide
error correction, data compression and speed conversion capabilities.
Error correction in your modem is via the ITU-T V.42 standard. Data
compression in the MT2834MR is either MNP Class 5 or ITU-T
V.42bis. The remainder of this chapter describes these features, and the
commands to operate them, as well as descriptions of related
commands.
Error correction is incorporated via the ITU-T V.42 standard. V.42
actually uses two error correction protocols, LAP-M and MNP Class 3
& 4. MNP Class 3 & 4 error correction emerged as the industry
standard among modem manufacturers over the past decade. It's now in
the public domain, and has been implemented in dozens of modem
brands that offer error correction with world wide installations in the
hundreds of thousands of units. LAP-M error correction is similar to
MNP Class 3 & 4. They both convert asynchronous data characters to a
synchronous data stream.
The MT2834MR provides two types of data compression: V.42bis and
MNP Class 5. V.42bis is newer and it requires concurrent error
correction using LAP-M. V.42bis is a very efficient data compression
technique that can provide up to a 4-to-1 compression, depending on
the type of files transmitted. MNP Class 5 data compression requires
concurrent error correction using MNP Class 3 & 4. It is an older and
more established standard that offers data compression in the 2-to-1
range (also dependent on the type of data).
The speed conversion feature allows the modem to operate at one speed
over the telephone lines and another speed at the RS232C serial port.
This allows the computer or terminal to communicate with the modem
at a fixed speed of up to 115,200 bps, while the modem operates at
various speeds up to 28,800 bps. This is vital if data compression is to
be effective (your terminal or computer must present data to the phone
line at a higher speed than which the modem is sending it over the
phone line).
This chapter also covers commands that control error correction, turn
data compression on and off and others that are related to high
performance operation along with the changes in the result codes.
5.2 How V.42 Detects and Corrects Errors
Some of the better known software-based error-correction protocols
include XMODEM and Kermit (for asynchronous file transfer
software), X.PC (Tymnet's own asynchronous software protocol), and
SDLC and HDLC, two popular synchronous protocols common in the
IBM mainframe environment. V.42 is functionally similar to SDLC and
HDLC, with some extras.
The main advantage of hardware-based V.42 error correction over these
software-based protocols is in "throughput". Throughput is the effect
that the use of the protocol has on the overall data rate. For example,
V.42 transmissions using a 2400 bps modem have an effective
throughput of about 2600 bps. The same modem using software-based
X.PC would have an effective throughput of less than 2400 bps.
Another way of stating it is that V.42 has an efficiency of about 108%,
while X.PC has an efficiency of about 91%.
Simply stated, one modem with V.42 sends coded data to another
modem with V.42, and the receiving modem is able to determine if
there were any errors. If there were, the receiving modem tells the
sending modem to resend the errant data until it's correct.
Technically speaking, when using V.42, the "sending" modem uses a
polynomial function to calculate a 16-bit number which is a function of
all the data sent in a particular "message" or "block", and then sends
those sixteen bits at the end of the block. (The "block" can include up to
256 characters.) The "receiving" V.42 modem, as it is receiving the
block, calculates its own version of the 16-bit number. Then it
compares its number with the 16-bit number sent with the block. If the
numbers are the same, the block is free from errors. If the numbers are
different, an error has occurred somewhere in the block. That's how
errors are detected.
Once an error is detected, the receiving modem's V.42 error correction
is activated.
For all practical purposes, the result of the V.42 error correction
protocol is error-free transmission. Using the 16-bit redundancy check,
it will detect every error which is 16 bits or smaller, with 100%
probability. As a result, the chances of an error occurring are actually so
small that you can, in practice, ignore them.
5.3 Data Compression
The MT2834MR has both V.42bis and MNP class 5 data compression.
ITU-T V.42bis is an international data compression standard which can
provide data compression of up to four to one in certain types of data.
MNP class 5 is a proprietary technique for data compression that
provides a data compression capability of two-to-one.
The MT2834MR must be in error correction mode before it can
compress data (LAP-M error correction for V.42bis data compression
or MNP error correction for MNP 5 data compression). By using the #L
command, you can select which error correction to use.
The type of file transfer protocol used to send and receive data will
have a big effect on the speed gain due to compression. In general, a
protocol which uses large data blocks transfers files quicker. For
example, YMODEM sends 1000 characters per block. It will also help
to have the serial port of the receiving modem set to the highest
possible speed (115,200 bps), if the sending modem is set to a lower
speed.
To achieve a data rate which is higher than the modem baud rate, use
the modem's speed conversion features by turning Baud Adjust off
($BA0) and operate the serial port at a higher speed than the modem
baud rate. For example, the serial port must be set to 4800, 9600,
19200, 38400, 57600, or 115,200 bps ($SB115200).
To use data compression, the modem must to be driven at full capacity.
In other words, the data needs to be present at enough volume (file
transfers or batch operations) and speed to get maximum compression
benefits. The modem speed conversion features must be used to utilize
the port at a higher speed than the modem connection speed. Data
compression works by locating repeated strings of characters and
repeating these strings using shorter codewords.
When operating the serial port at a higher speed than the modem baud
rate, some type of flow control should be used, otherwise data can be
lost. (See &E4 and &E5 commands.)
To enable data compression, type AT&E15 and hit ENTER; to disable
data compression, type AT&E14 and hit ENTER.
Note: For data compression to take place, both the answer and originate
modems must have data compression and error correction enabled.
5.4 MNP Classes
The MNP protocol is divided into several levels, or "Classes". The
classes you would encounter today in full duplex dial-up in 1200, 2400
and 9600 bps modems are Classes 2 through 5. When modems
equipped with MNP start communicating, they will negotiate operation
to the highest common MNP class between them and operate at that
level.
5.5 V.42 Mode Select Command (#L)
The V.42 Mode Select command (#L) selects which type of error
correction your MT2834MR will use for transmissions. The V.42
standard implements both MNP Class 3 & 4 and LAP-M error
correction protocols, and by executing one of the #L commands you are
instructing your MT2834MR how to operate with each protocol. For
example, the factory default setting (#L0) tells your MT2834MR to
negotiate the protocol with the remote modem, and to prefer MNP 3 &
4.
The following details the operation of the #Ln command:
1. #L0 Command (factory default setting)
The #L0 Command allows a pair of modems to negotiate
which V.42 mode (MNP or LAP-M) will be used.
Originate Mode
a. If both modems have LAP-M capability, the modems
will use LAP-M mode.
b. If one or both modems do not have LAP-M capability
and both have MNP, the modems will use the MNP.
Answer Mode
a. The answering modem will respond to either an MNP
Link Request or LAP-M ODP signal, depending
on which is issued by the originating
Modem.
2. #L1 Command
The #L1 Command enables MNP error correction and disables
LAP-M. This command is for Originate mode only. Answer mode still
accepts MNP or LAP-M.
3. #L2 Command
The #L2 Command enables LAP-M error correction and
disables MNP. This command is for Originate mode only. Answer
mode still accepts MNP or LAP-M.
4. #L3 Command
In the above commands, the modems use a two-phase process
to establish a V.42 connection ("Detection" to establish
whether the remote modem is also error correcting, and
"Protocol Establishment" to determine
parameters and establish the error correction connection). If
you know that the other modem is a V.42 error
correcting modem, and you wish to use LAP-M, the #L3
command to disable the Detection phase and go directly to
Protocol Establishment. Both modems must have #L3 in
effect.
5.6 Modes of Operation
You can configure your MT2834MR in one of three different V.42
modes of operation (each mode can be with or without compression).
These are the Normal, Reliable and Auto-Reliable modes. The modes
and data compression features are selected with commands covered in
Section 5.13.
Normal Mode (&E0)
In the Normal mode of operation, the MT2834MR's error correction
capabilities are disabled, and the modem functions as a normal (non-
error-correcting) modem.
Reliable Mode (&E2)
In Reliable mode, the MT2834MR uses its V.42 error correction
capabilities during all transmissions. When in Reliable mode, the
MT2834MR must be connected to another modem with a similar V.42
protocol activated (MNP or LAPM). If the modems cannot establish a
V.42 error correction connection, the modem will time out and hang up.
Auto-Reliable Mode (&E1)
In Auto-Reliable mode, the MT2834MR will, during the handshaking
procedures at the start of the on-line connection, automatically
determine whether or not the modem with which it is communicating is
using the error correction. If the MT2834MR determines that the other
modem is using V.42, it will switch itself into the Reliable (V.42) mode
of operation. If it is determined that the other modem is not using V.42,
the MT2834MR will remain in Normal mode.
The method the MT2834MR uses to determine if the V.42 modem
involves the use of a "Link Request". When the MT2834MR is in Auto-
Reliable mode and originates a call, it goes through normal
handshaking procedures just like any dial-up modem. After establishing
the on-line connection, the MT2834MR transmits a Link Request
message to the answering modem. If the answering modem replies with
an appropriate V.42 acknowledgment response, the MT2834MR
switches into Reliable mode. Otherwise, it will stay in Normal mode.
This V.42 handshaking procedure generally takes about five seconds.
When operating in V.42 Reliable mode, the MT2834MR uses its
memory, or buffer, to store data as it is received. During periods of
error-caused retranmissions or compression slowdowns, this buffer may
fill up. To prevent buffer overflow and subsequent loss of data, the
modem uses flow control to signal the computer attached to its RS232C
port that the modem buffer is close to being full. This causes the
computer to pause in its data transmission until the modem is able to
empty its buffer sufficiently to accept more data, at which time the
modem signals the computer that it may resume transmission.
5.7 Introduction to Flow Control
Flow control refers to the techniques used by computer devices to stop
and restart the flow of data from each other. Flow control is necessary
so that a device does not receive more data than it can handle. In the
case of the MT2834MR, there is a need for flow control in both
directions. Flow control for data passing from your computer to the
modem is called Modem-Initiated Flow Control and flow control for
data passing from the modem to your computer is called
Computer/Terminal-Initiated Pacing.
The MT2834MR supports both hardware and software Modem Initiated
Flow Control, and, on the Computer/Terminal-Initiated Pacing side,
supports hardware and software flow control, and a special version used
by Hewlett Packard compatible systems called ENQ/ACK Pacing. The
MT2834MR allows hardware and software pacing to be passed through
the modem to the other end of the link so that your computer or
terminal can control data start/stop activity through your modem. This
is called "Xon/Xoff Pass-Through".
To state it simply, "Flow Control" is something the modem does to the
computer, while "Pacing" is something the computer does to the
modem.
5.8 Modem-Initiated Flow Control
When operating in the V.42 Reliable mode, the MT2834MR uses its
memory, or buffer, to store data as it is received. During periods of
error-caused retransmissions or compression slowdowns, this buffer
may fill up. To prevent buffer overflow and subsequent loss of data, the
modem uses flow control to signal the computer attached to its RS232C
port that the modem buffer is close to being full. This causes the
computer to pause in its data transmission until the modem is able to
empty its buffer sufficiently to accept more data, at which time the
modem signals the computer that it may resume transmission.
The MT2834MR gives you two choices for methods of modem-
initiated flow control. (You also have a third choice, which is to not use
flow control at all.) One choice is "Xon/Xoff", which uses special
characters in the data transmissions. The other is "Hardware Flow
Control", which uses the CTS output lead on the RS232C interface
(Clear to Send - Pin 5). Most terminals and computers support one or
both of these methods.
Xon/Xoff Flow Control (&E5)
Xon/Xoff is the most commonly-used method of flow control.
Under this method, control characters known as "Xon" and "Xoff" are
inserted by the modem into the data to start and stop the flow of data
from the computer or terminal to which the modem is attached. Xoff,
(CTRL-S), stops the flow of data, and Xon, (CTRL-Q), restarts it. With
regards to binary data, Xoff/Xon flow control is not recommended
because an Xoff character may be part of the data and would trigger an
Xoff of the modem or software package, which would halt data flow.
Hardware Flow Control (&E4)
With Hardware Flow Control, the modem uses its RS232C
interface to control the flow of data from the computer or terminal to
which it is attached. The CTS (Clear to Send) signal on Pin 5 of the
RS232C interface is brought low to stop the flow of data, and is brought
high to restart it.
When you select Hardware Flow Control as your Modem-
Initiated Flow Control method, you are also selecting it for Pacing. The
difference between the two, however, is that Modem-Initiated Flow
Control uses the Pin 5 CTS output signal, while Pacing uses the Pin 4
RTS input signal. (Refer to Section 5.9.)
Modem commands are used to select the method of flow control used
by the MT2834MR when its error correction capabilities are used.
These commands are covered in Section 5.13. If neither method is
selected, the modem will default to no flow control.
5.9 Terminal/Computer-Initiated Pacing (&E13)
As mentioned earlier, the MT2834MR can initiate flow control by
issuing Xon/Xoff commands or by toggling the CTS signal on the
RS232C interface. The modem can also be configured to react to
similar commands and signals from the computer or terminal to which it
is attached via the RS232C interface.
We refer to computer or terminal initiated flow control as "Pacing".
When the modem is set for Pacing On, the modem responds to the
terminal or computer pacing. When the modem is set for Pacing Off, it
will ignore pacing.
In order for the MT2834MR to be set for Pacing On, a modem-initiated
method of flow control must be previously selected. Once this is done,
the MT2834MR will respond to either Xon/Xoff commands, or to the
toggling of the RTS (Request to Send) signal on Pin 4 of the RS232C
interface, depending on what you selected earlier as your Modem-
Initiated Flow Control method.
If you use RTS pacing, be sure that the RTS DIP-Switch is set so that
RTS is not forced on (see Section 7.3).
5.10 Xon/Xoff Pass-Through (&E7)
So far, you have had three choices to make regarding pacing. You can
set the modem to respond to Xon/Xoff pacing, or to respond to RTS
pacing, or you can set the modem to ignore pacing completely.
Another choice you can make (which actually can apply to both pacing
and modem-initiated flow control, although it applies mainly to pacing)
is called "Xon/Xoff Pass-Through". This means that if your modem is
set to respond to Xon/Xoff commands, you can have the modem do one
of the following.
1. The modem responds to the Xon and Xoff pacing commands
while at the same time allowing these commands to pass
through the modem and on to the remote location. We
call this "Respond, Pass-Through".
2. The modem responds to Xon/Xoff pacing, but does not allow
the pacing signals to pass through the modem and on to
the remote location. We call this "Respond, No Pass-
Through".
When Xon and Xoff commands are allowed to pass through the
modem, the computer (or terminal) at the remote site receives these
commands, and depending on how it is configured, the computer (or
terminal) may respond to them also.
5.11 Normal Mode Modem Flow Control (&E10 and &E11)
When two MT2834MR's are connected in Normal mode (not using
error correction), Xon/Xoff can be used to control the flow of data
between the modems. Flow control can be turned on or off with the
Normal Mode Modem Flow Control commands. When the modems are
connected in Reliable mode, a different method of modem flow control
is used, and the commands for Normal Mode Modem Flow Control are
ignored.
When using Speed Conversion in Normal mode, you must activate the
modem's Normal Mode Modem Flow Control. (Speed Conversion is
explained in Section 5.15.)
5.12 Hewlett Packard ENQ/ACK Pacing (&E9)
If the MT2834MR is used with Hewlett Packard (or similar) equipment
that employs ENQ/ACK pacing, the modem can be configured to
respond to ENQ/ACK commands, making it compatible with HP
systems. Doing so does not effect any other flow control or pacing
already configured in the modem.
When configured for ENQ/ACK, the ENQ (CTRL-E) and ACK
(CTRL-F) signals from the HP equipment will be accepted and
responded to according to Hewlett Packard protocol.
5.13 Compression, Error Correction, Flow Control,
Pass Through and Pacing Commands
The MT2834MR has a variety of commands to control its error
correction and data compression options. These commands are listed
below. (Remember to precede each command with the AT characters.)
Normal/Auto-Reliable/Reliable Mode Commands:
&E0 = Normal Mode (prevents any error correction mode)
&E1 = Auto-Reliable Mode* (enables MNP or LAP-M mode)
&E2 = Reliable Mode (MNP or LAP-M mode only)
Modem-Initiated Flow Control Commands:
&E3 = Disables flow control (no flow control)
&E4 = Hardware flow control (CTS on/off and RTS on/off)*
&E5 = Xon/Xoff flow control
Xon/Xoff Pass-Through Commands:
&E6 = Modem responds to Xon/Xoff characters, but does
not allow Xon/Xoff characters to pass through to
remote site.*
&E7 = Modem responds to Xon/Xoff characters, and allows
them to pass through to remote site.
Enq/Ack Pacing Commands:
&E8 = Enq/Ack method of pacing off*
&E9 = Enq/Ack method of pacing on
Normal Mode Modem Flow Control Commands:
&E10 = Normal Mode Modem Flow Control off*
&E11 = Normal Mode Modem Flow Control (Xon/Xoff) on
Computer (or Terminal)-Initiated Flow Control(Pacing) Commands:
&E12 = Pacing off
&E13 = Pacing on (either RTS on/off or Xon/Xoff depending
on the setting of &E4 or &E5).*
*Factory default setting
**The factory default setting for data compression is enabled, but the
modem will not compress data (&E15) unless &E1 (auto-reliable mode)
or &E2 (reliable mode) is also selected.
Data Compression Commands:
&E14 = Data Compression disabled
&E15 = Data Compression enabled**
*Factory default setting
**The factory default setting for data compression is enabled, but the
modem will not compress data (&E15) unless &E1 (auto-reliable mode)
or &E2 (reliable mode) is also selected.
5.14 Error Correction Result Codes
When the MT2834MR is operating with error-correction enabled, five
of its responses are altered, to let you know that you have made a
connection in Reliable mode. These Result Codes for a V.42 MNP
connection are listed below:
Verbose Terse
CONNECT RELIABLE 1R
CONNECT 1200 RELIABLE 5R
CONNECT 2400 RELIABLE 9R
CONNECT 4800 RELIABLE 11R
CONNECT 9600 RELIABLE 12R
CONNECT 14400 RELIABLE 13R
CONNECT 19200 RELIABLE 19R
CONNECT 21600 RELIABLE 21R
CONNECT 24000 RELIABLE 24R
CONNECT 26400 RELIABLE 26R
CONNECT 28800 RELIABLE 28R
The result codes for a V.42 LAP-M connection are listed below:
Verbose Terse
CONNECT LAPM 1L
CONNECT 1200 LAPM 5L
CONNECT 2400 LAPM 9L
CONNECT 4800 LAPM 11L
CONNECT 9600 LAPM 12L
CONNECT 14400 LAPM 13L
CONNECT 19200 LAPM 19L
CONNECT 21600 LAPM 21L
CONNECT 24000 LAPM 24L
CONNECT 26400 LAPM 26L
CONNECT 28800 LAPM 28L
These responses replace the CONNECT (1), CONNECT 1200 (5),
CONNECT 2400 (9), CONNECT 4800 (11), CONNECT 9600 (12)
and CONNECT 14400 (13) responses that the modem uses when in
Normal mode.
When data compression is enabled, the word COMPRESSED (verbose)
or letter C (terse) are also added to these responses.
In addition to these responses, the V.42 (Error Correction) LED lights
when the modem is in error correction (reliable) mode. The V42 LED
flashes on and off when the modem has data compression enabled.
* MNP 5 data compression can only be activated when using V.42 error
correction.
5.15 Speed Conversion
This section addresses the speed conversion feature available in the
MT2834MR. Speed conversion is a necessary part of data compression
since data must be presented to the phone line faster than it can handle
data, if compression is to be effective.
Speed conversion allows the MT2834MR to communicate at one speed
over the phone line, and at another speed at the RS232C interface. The
speed (also referred to here as "bps," or "baud rate") can be fixed at the
RS232C interface independently of the baud rate of the on-line
transmissions.
In addition to data compression, another popular application for speed
conversion involves an auto-answer MT2834MR connected to a
computer that does not have autobauding capability. This means that
the computer must be set at a fixed baud rate, regardless of whether the
modem is communicating over the phone line at 300, 1200, 2400, 4800,
9600, 14,400, 19,200, 21,600, 24,000, 26,400, or 28,800 bps. In this
application, speed conversion allows the modem to match its speed to
that of an in-calling modem, while at the same time communicating
with the attached computer through its RS232C port at a fixed baud
rate, which can be preselected at 300, 1200, 2400, 4800, 9600, 19,200,
38,400, 57,600, or 115,200 bps.
The flow control and pacing methods used between the computer and
the modem during speed conversion are the same as those used with the
V.42 error correction. The two choices (Xon/Xoff or RTS/CTS) are
selected with the &E commands detailed earlier in this chapter. If you
are not using the modem's V.42 error correction, you must activate
modem flow control with a separate command (&E11), as explained
earlier in Section 5.11.
There are three commands which relate specifically to speed
conversion. They are Baud Adjust ($BA), Modem Baud Rate ($MB)
and Serial Port Baud Rate ($SB).
$BA Baud Adjust
In typical operations, the MT2834MR will do one of two things
regarding speed. It will automatically match the speed (bps rate or
"baud rate") of its RS232C interface and phone line transmissions to
that of the terminal or computer to which it is attached as soon as it
receives its first AT command. Or, when in auto-answer mode, it will
match its RS232C and transmission speeds to that of the originating
modem that called it. This is typical for virtually all of today's dial-up
modems, and is referred to by various names, such as Auto-Speed or
Baud Adjust. Here we call it Baud Adjust.
When using speed conversion, set the modem so that it does not adjust
its speed at the RS232C serial port, even if the modem does adjust its
line transmission speed. To turn Baud Adjust off, type AT$BA0 (where
0 is "zero").
Note: Do not be misled by the meaning of turning Baud Adjust "off",
even though the term "Baud Adjust" sounds like it should mean the
same thing as "Speed Conversion". It actually means the opposite:
Turning Baud Adjust off turns Speed Conversion on.
Turning Baud Adjust on turns Speed Conversion off.
To turn Baud Adjust on (and Speed Conversion off), enter AT$BA1
and hit ENTER. The modem will now match its RS232C speed to that
of the computer, and will adjust its speed to any changes in the
computer's speed in the originate mode, or to the speed of the
originating modem when it's in the answer mode. With baud adjust on,
the speed at which the modem communicates over the phone line is
always be the same as the speed at which it communicates via its
RS232C serial port.
$MB Modem Baud Rate
The $MB command presets the MT2834MR's transmission baud rate
for originate operations, (i.e., the speed of the modem's transmissions
over the telephone lines when originating a call). With speed
conversion, this transmission speed can be a different baud rate than the
serial port speed.
When the MT2834MR receives (answers) a call from another modem,
it automatically switches its phone line transmission baud rate to match
the calling modem. However, if the MT2834MR originates a call to
another modem that is unable to connect at the baud rate of the
MT2834MR, the MT2834MR will automatically drop to a lower baud
rate in an attempt to match the speed of that modem. For example, if the
MT2834MR is set for 28,800 bps and calls another modem that has a
top speed of 9600 bps, it will drop to 9600 bps.
To set the Modem Baud Rate, type AT$MBn, where n can be 75 (in
ITU-T V.23 mode) 300, 1200, 2400, 4800, 9600, 14,400, 19,200,
24,000, or 28,800 bps as listed below:
AT$MB75 = ITU-T V.23
AT$MB300 = 300 bps
AT$MB1200 = 1200 bps
AT$MB2400 = 2400 bps
AT$MB4800 = 4800 bps
AT$MB9600 = 9600 bps
AT$MB14400 = 14400 bps
AT$MB19200 = 19200 bps
AT$MB24000 = 24000 bps
AT$MB28800 = 28800 bps
The factory default setting is 28,800 bps.
If Baud Adjust is on ($BA1), speed conversion is off, as we discussed
earlier. This means that the $MB command is also ignored, since it is
part of speed conversion.
$SB Serial Port Baud Rate
The $SB command presets the speed of the MT2834MR's serial
(RS232C) port, in both the originate and answer modes. Speed
conversion allows you to set this serial port baud rate at a fixed speed of
up to 115,200 bps, regardless of the modem's transmission speed
setting.
For this command to work, the modem's Baud Adjust feature must first
be turned off with the $BA command.
In addition to the MT2834MR's serial port speed being set by this
command, the default speed at which the modem issues Command
mode responses (result codes) is also set.
The MT2834MR will accept AT commands at any speed, regardless of
the speed preset by the $SB command. If the modem receives such a
command at a speed that is different than the preset speed, the modem
will switch its serial port baud rate to match the new AT command
speed, although the baud rate value stored by the $SB command will
remain the same. This provides you with a convenient way to switch the
serial port speed, while still making it easy to go back to the original
speed automatically the next time the modem is powered up or reset
with an ATZ command.
To set the Serial Port Baud Rate, type AT$SBn, where n can be 300,
1200, 2400, 4800, 9600,19,200, 38,400, 57,600, or 115,200 bps as
listed below:
AT$SB300 = 300 bps
AT$SB1200 = 1200 bps
AT$SB2400 = 2400 bps
AT$SB4800 = 4800 bps
AT$SB9600 = 9600 bps
AT$SB19200 = 19200 bps
AT$SB38400 = 38400 bps
AT$SB57600 = 57,600 bps
AT$SB115200 = 115,200 bps
The factory default setting is 115,200 bps.
5.16 Related Commands
$A Auto-Reliable Buffering
In Auto-Reliable mode, the modem is given four seconds to establish a
Reliable connection. After the four seconds, the modem will drop to
Normal mode. Any data received during this period is normally
discarded. The $A command is used to cause the modem to buffer
(save) data that is received during the Auto-Reliable time-out period.
This data is then output by the modem after the CONNECT message.
Type AT$A0 to discard data received during the Auto Reliable time
period.
Type AT$A1 to buffer data received during the Auto Reliable time
period.
The factory default setting is $A0.
&BS Maximum Block Size
The maximum size of Reliable mode data blocks is controlled with the
&BS command. MNP Class 3 sends blocks of 1 to 64 characters. MNP
Classes 4 and 5 normally send blocks of 1 to 256 characters. Reducing
the block size for Classes 4 and 5 to 64 characters may give a smoother
flow of data, and better throughput performance on noisy phone lines.
Using smaller block sizes over good phone lines may cause a slight loss
in data throughout speed.
Type AT&BS0 for a maximum transmit block size of 64 characters.
Type AT&BS1 for a maximum transmit block size of 256 characters.
The factory default setting is &BS1.
$F Enable/Disable Auto-Reliable Fallback Character
In Auto-Reliable mode, the modem is given four seconds to establish a
Reliable connection. If a single CARRIAGE RETURN is received from
the remote modem during this four second period, the Auto-Reliable
modem will assume that the remote modem is not in Reliable mode and
will drop to a Normal connection. The CARRIAGE RETURN character
will then be output following the CONNECT message. The
CARRIAGE RETURN is the only character which will cause the
modem to drop to Normal mode. Any other data will either be buffered
or discarded.
The $F command is used to disable this fallback-to-Normal-due-to-
CARRIAGE-RETURN feature. The Auto-Reliable fallback character
($F) and auto reliable buffering ($A) commands can be used together,
to cause the modem to buffer all data received up until the CARRIAGE
RETURN and then drop to Normal mode. All data received will then be
output following the CONNECT message.
Type AT$F0 to cause the modem to not fall back to normal connect if a
CARRIAGE RETURN is received.
Type AT$F1 to cause the modem to fall back to normal connect if a
CARRIAGE RETURN is received.
The factory default setting is $F1.
#P Parity Selection
The #P command enables the setting of Callback modem parity for the
prompt message sent by the Callback modem. AT#P0 selects no parity.
AT#P1 selects odd parity. AT#P2 selects even parity.
The factory default setting is #P0.
$R Retransmit Count
If errors are received during a Reliable connection, the modem will re-
send the block of data which contained an error. If another error occurs,
the block will be re-sent again. The modem counts the number of times
that a data block is re-sent. If the same block of data is resent 24 times
and still has not been received properly, the modem will abort the
connection, as dictated by the AT$R0 command.
This retransmit counter can be disabled with the $R1 command. When
the retransmit counter is disabled, the modem will keep trying to send
data and will not abort, not matter how many times the same block is
resent.
Type AT$R0 to disconnect if the retransmit count is exceeded.
Type AT$R1 to not disconnect due to excessive retransmits.
The factory default setting is $R0.
$E V.42 Error Correction at 300 bps
At 300 bps, error correction is not normally used. $E1 lets the
MT2834MR to function in either Normal (&E0), Auto-Reliable (&E1)
or Reliable (&E2) mode. $E0, which is the factory default setting,
disables V.42 error correction altogether.
5.17 Summary
This chapter has covered the commands necessary for the MT2834MR
to operate as a V.42 device. Briefly, we'll summarize these sections
here. If something here doesn't seem clear, now may be a good time to
refer to the appropriate section.
V.42 error correction is built into the MT2834MR's hardware, and
detects virtually 100% of transmission errors, which are usually caused
by noisy phone lines. When errors are detected, the V.42 protocol
causes the modem to retransmit the errant data block.
V.42bis and MNP data compression, also built into the MT2834MR's
hardware, provides an effective throughput higher than the modem's bps
transmission speed. The amount of increase depends on the type of data
being transmitted.
The MNP protocol is divided into several "classes", which for our
purposes are numbered 2 through 5. The MT2834MR uses all of these
MNP classes, which yields a higher throughput and error free
transmissions. LAP-M provides another type of error correction.
The MT2834MR can be set for three different modes of operation,
along with activating data compression in Reliable mode. Normal mode
disables error correction, Reliable mode enables it, and Auto-Reliable
mode allows the modem to automatically turn V.42 on when it detects
its use in another modem.
Flow control methods are used by the MT2834MR to prevent data loss
from buffer overflow. The modem can both initiate it ("flow control")
and respond to it ("pacing"), using either Xon/Xoff commands or
RS232C signaling via CTS (from the modem) or RTS (from the
computer or terminal). Hewlett Packard ENQ/ACK pacing is also
supported. If needed, Xon/Xoff commands can be "passed through" the
modem to a remote computer or terminal.
The MT2834MR's speed conversion feature allows it to operate at one
speed over the telephone lines and another speed at the RS232C serial
port. This allows the computer or terminal to communicate with the
modem at a fixed speed of up to 115,200 bps, while the modem
operates at various speeds up to 28,800 bps. This ability is vital if data
compression is to be effective (your terminal or computer must present
data to the phone line at a higher speed than which the modem is
sending it over the phone line).
This concludes what is probably the most difficult chapter in this
manual, covering techniques that bewilder many modem users. If you
feel that you have mastered these concepts of Error Correction, Data
Compression, and Speed Conversion, congratulations!
6.1 Introduction
The MT2834MR has four diagnostic test features. The first is an
automatic self test done each time the modem is powered up. This test
checks the modem's processor timing and memory chips. The modem's
front panel LEDs (refer to Chapter 1) display the progress of the self-
test.
The CCITT V.54 Loopback Testing capability supports telephone
circuit and transmission problem isolation. If Pin 8 on the RS232
interface goes high, the MT2834MR goes into analog loopback mode.
The other tests are initiated with the MultiModemManager Software as
explained in the MultiModemManager Owner's Manual.
7.1 Introduction
There are 3 sets of DIP-Switches and 3 two-position jumpers on the
MT2834MR card. To remove the MT2834MR modem card from the
CC4800 rack, pull the ejector levers away from the rack (if necessary
loosen the retaining screw first), then carefully slide the modem card
out of the rack.
The DIP-Switches are used to enable or disable various user-selectable
options. Each DIP-Switch is set to a factory default setting that is useful
in most applications. Each set of DIP-Switches is labeled with a number
and can be set to either the UP (marked "OPEN") or Down position.
The individual switches can easily be set with your fingernail or a
pencil tip.
Note: Before changing any DIP-Switches on the MT2834MR, please
consult your MultiModemManager software manual. Many of these
options can be controlled by the software.
Each of the 3-pin (two-position) jumpers is used to select options. They
are also pre-set to factory default settings that should be effective for
your application. The default setting can be easily changed to an option
setting by removing the shorting plug and replacing in the option
position.
The following sections detail the function of each DIP-Switch and
jumper located on the MT2834MR PC board.
7.2 16-Position DIP-Switches
The MT2834MR PC board contains three pairs of DIP-Switch blocks.
Each pair of DIP-Switch blocks is numbered 1-12 and 13-16, and each
pair of DIP-Switch blocks is related to each of the three on-board
modems.
7.3 16-Position DIP-Switch Settings
Each individual switch, numbered 1-12 and 13-16, and can be set to
either the Up (marked "OPEN") or Down position. Each of these DIP-
Switches controls the following functions for its corresponding on-
board modem.
7.3.1 DIP-Switches #1 - #12
Switch #1
Forced DTR - "DTR"
(Asynchronous/Synchronous Mode/Leased Line/Dial-Up)
The MT2834MR must have a high DTR signal in order to operate. This
signal is provided to each modem by the terminal or computer to which
it is attached, through the RS232/V.24 interface on pin 20. If your
terminal is not providing DTR to the modem, you can force the DTR
signal DIP-Switch #1.
DTR function normally = Switch #1 UP
DTR forced ON = Switch #1 DOWN
(Factory Default Setting = UP)
Switch #2
Flow Control - &E4/&E5
(Asynchronous Mode/Leased Line/Dial-Up)
With Hardware Flow control, the modem uses its RS232C/V.24
interface to control the flow of data from the computer or terminal to
which it is attached. CTS signal on Pin 5 of the RS232C/V.24 is
brought low to stop the flow of data, and is brought high to restart it.
Place DIP-Switch #2 in the UP position to enable Hardware Flow
control (&E4). Xon/Xoff Flow control (&E5) is another method of flow
control in which Xon/Xoff characters in the data dictates the start and
stop of data flow from the computer or terminal. Place DIP-Switch #2
in the DOWN position to enable Xon/Xoff Flow control.
Hardware Flow Control (&E4) = Switch #2 UP
Xon/Xoff Flow control (&E5) = Switch #2 DOWN
(Factory Default Setting = UP)
Switch #2
SDLC/BSC Selection
(Synchronous Mode/Leased Line/Dial-Up)
Synchronous Data Link Control (SDLC) and Binary Synchronous
Control (BSC) are two error correction protocols used in the IBM
Mainframe environment. Place DIP-Switch #2 in the UP position to
select SDLC mode. Place DIP-Switch #2 in the DOWN position for
BSC mode.
SDLC Mode = Switch #2 UP
BSC Mode = Switch #2 DOWN
(Factory Default Setting = UP)
Switch #3
Enable/Suppress Responses - "Q"
(Asynchronous Mode/Dial-Up)
In some applications in Asynchronous mode, you may want to suppress
all responses from the modem. Place DIP-Switch #3 in the DOWN
position to enable result code responses (Q0). Place DIP-Switch #3 in
the UP position for answer mode without responses and echo off, (but
with originate still intelligent)(Q2).
Enable Responses: Originate/Answer (Q0) = Switch#3 DOWN
Suppress Responses: Answer (Q2) = Switch #3 UP
(Factory Default Setting = DOWN)
Switch #3
dB Transmission Levels
(Asynchronous/Synchronous Mode/Leased Line)
The MT2834MR can adjust to dB transmission levels required by some
phone carriers. With DIP-Switch #3 in the DOWN position, the
MT2834MR transmits at 0 db. With DIP-Switch #3 in the UP position,
transmission is at -10dB.
0dB Transmission = Switch #3 DOWN
-10dB Transmission = Switch #3 UP
(Factory Default Setting = UP)
Note: dB transmission levels on International models may be different
from those values shown above.
Note: Switch #3 has no effect in leased line mode in the MT2834MRK.
Switch #4
AS/400 Mode
(Synchronous Mode/Leased Line/Dial-Up)
The MT2834MR can function in an IBM AS/400 environment. Place
DIP-Switch #4 in the DOWN position to cause the MT2834MR to
operate via IBM command set.
Place DIP-Switch #4 in the UP position to disable AS/400 mode
Note: The MT2834MR must be in Command mode to allow AS/400
mode operation).
AS/400 Mode Enabled = Switch #4 DOWN
AS/400 Mode Disabled = Switch #4 UP
(Factory Default Setting = UP)
Switch #4
UNIX UUCP Spoofing
(Asynchronous Mode/Leased Line/Dial-Up)
The MT2834MR can be used with UNIX equipment which employs
ACK flow control to monitor data integrity. The MT2834MR can do
UUCP "spoofing", where the modem is able to generate ACKs at the
DTE interface. Data is then transmitted more time-efficiently, because
the delay of waiting for data to be received then for the ACK to be
returned at the remote end is eliminated. Place DIP-Switch #4 in the
DOWN position to enable UUCP spoofing.
UUCP Spoofing Enabled = Switch #4 DOWN
UUCP Spoofing Disabled = Switch #4 UP
(Factory Default Setting = UP)
Switch #5
Disable Auto-Answer - "Ans"
(Asynchronous Mode/Synchronous Mode/Dial-Up)
In some originate-only applications, you may wish to disable the
MT2834MR's automatic answering capabilities. This may be true if you
have a telephone set attached to a modem and wish to receive voice
calls that you yourself would answer instead of the modem.
Auto-Answer Enabled = Switch #5 UP
Auto-Answer Disabled = Switch #5 DOWN
(Factory Default Setting = UP)
Switch #5
Originate/Answer Mode
(Asynchronous/Synchronous Mode/Leased Line)
The MT2834MR can function in either Originate mode or Answer
mode. To enable Answer mode, place DIP-Switch #5 in the UP
position. To enable Originate mode, place DIP-Switch #5 in the
DOWN position.
Origination Enabled = Switch #5 DOWN
Answer Enabled = Switch #5 UP
(Factory Default Setting = UP)
Switch #6
Maximum Throughput Setting
(Asynchronous Mode/Leased Line/Dial-Up)
In some applications, you may want to dial into services with maximum
throughput on. Other applications require maximum throughput off
(e.g., service not supporting error correction, or the V.42 handshake
interferes with logon sequence). Switch #6 controls three important
parameters, which in effect enable or disable maximum throughput
(error correction, speed conversion and serial port speed).
Maximum Throughput Enabled = Switch #6 UP
Maximum Throughput Disabled = Switch #6 DOWN
(Factory Default Setting = UP)
Switch #6
Slave Clocking
(Synchronous Mode/Leased Line/Dial-Up)
In Synchronous mode, DIP-Switch #6 controls the timing at the receive
clock. The originating side, in effect, adjusts to the timing at the remote
("slave") side.
Slave Clocking Enabled = Switch #6 DOWN
Slave Clocking Disabled = Switch #6 UP
(Factory Default Setting = UP)
Switch #7
Request To Send Forced - "RTS"
(Asynchronous/Synchronous Mode/Leased Line/Dial-Up)
If your computer or terminal uses RTS-CTS protocol (normally used in
synchronous applications, but also if you are using hardware pacing for
V.42 error correction or speed conversion), you may want to switch
RTS to function independent of CTS (DIP-Switch #7 UP). For most
applications, especially asynchronous, Switch #7 should be set so that
RTS is forced on (DIP-Switch #7 DOWN).
RTS functions Normally = Switch #7 UP
RTS forced ON = Switch #7 DOWN
(Factory Default Setting = DOWN)
Switch #8
Enable/Disable Command Mode - "Com"
(Asynchronous/Synchronous Mode/Leased/Dial-Up)
In some applications you may want to disable Command mode so that
the modem will not recognize or react to AT or any other commands.
This may be true in strictly auto-answer applications where no call
origination will be required. DIP-Switch #8 enables or disables the
modem's ability to recognize Command mode characters. The factory
default setting is Command mode enabled.
Disable Command Mode = Switch #8 UP
Enable Command Mode = Switch #8 DOWN
(Factory Default Setting = DOWN)
Switch #9
No function.
Switch #10
Leased Line/Dial-Up Operation - "DDD"
(Asynchronous/Synchronous Mode/Leased Line/Dial-Up)
The MT2834MR can operate in both leased-line or dial-up modes. This
switch controls leased-line/dial-up operation. For dial-up operation,
place DIP-Switch #10 in the UP position. For leased-line operation,
place DIP-Switch #10 in the DOWN position.
Dial-Up Operation = Switch #10 UP
Leased Line Operation = Switch #10 DOWN
(Factory Default Setting = UP)
Switch #11
"AT" Responses/Multi-Tech Responses
(Asynchronous Mode/Leased Line/Dial-Up)
In Asynchronous mode (DIP-Switch #12 DOWN), the MT2834MR
responds with result codes according to the Multi-Tech command
response set or with the "AT" command response set (DIP-Switch #11
in the UP position). The &Q command performs the same function of
choosing AT or Multi-Tech responses and is explained further in
Chapter 5.
"AT" Responses (&Q1) = Switch #11 UP
Multi-Tech Responses (&Q0) = Switch #11 DOWN
(Factory Default Setting = DOWN)
For more information on Result Codes, refer to Chapter 3.
Switch #11
Internal/External Clocking
(Synchronous Mode/Leased Line/Dial-Up)
With the MT2834MR in Synchronous Mode, the transmit clock can be
supplied by the DTE on pin 24 of the RS232C/V.24 interface by DIP-
Switch #11 positioned UP. DIP-Switch #11 in the DOWN position
enables the DCE to control clocking.
External Clock (pin 24) = Switch #11 UP
Internal Clock (pins 15/17) = Switch #11 DOWN
(Factory Default Setting = DOWN)
Switch #12
Asynchronous/Synchronous Operation - "Sync"
(Asynchronous/Synchronous Mode/Leased Line/Dial-Up)
The MT2834MR can operate in both asynchronous mode and
synchronous mode. When in synchronous mode, start and stop bits are
eliminated. The modem's internal clock circuits on the RS232C/V.24
pins 15 and 17, are activated. The MT2834MR's Command Mode will
not be accessible in the synchronous mode. For synchronous operation,
you may want to set the RTS forcing and CTS forcing DIP-Switches so
that both of signals act normally (not forced on).
Synchronous Operation = Switch #12 UP
Asynchronous Operation = Switch #12 DOWN
(Factory Default Setting = DOWN)
7.3.2 DIP-Switches #13 - #16
Switches #13 and #14 - Speed Selection
DIP-Switches #13 and #14 are used for speed selection (mainly in call
origination leased line applications).
DIP-Switch
28800 bps Operation #13 #14
UP UP
19200 bps Operation #13 #14
DOWN UP
14400 bps Operation #13 #14
UP DOWN
9600 bps Operation #13 #14
DOWN DOWN
NOTE: The modem baud rate command, $MB, overrides the
setting of DIP-Switches #13 - #14.
Switch #15
Carrier Detect/DSR Source - "DSR"
(Asynchronous/Synchronous Mode/Dial-Up/Leased Line)
Some terminals react in unusual ways to the toggling of the Carrier
Detect (CD - RS232C/V.24 pin 6) signals. The most common symptom
is that the modem will not respond to commands, or will not echo
characters. In these cases, force these two signals On in order for the
terminal to communicate properly with the modem when the modem is
in Command mode by placing DIP-Switch #15 in the DOWN position.
With Switch #15 UP, the state of the CD and DSR signals depend on
the On-Line status.
CD and DSR normal = Switch #15 UP
CD and DSR forced On = Switch #15 DOWN
(Factory Default Setting = UP)
Switch #16
2-Wire/4-Wire Leased Line
(Asynchronous/Synchronous Mode/Leased Line)
2-Wire Leased Line = Switch #16 UP
4-Wire Leased Line = Switch #16 DOWN
(Factory Default Setting = DOWN)
7.4 Jumper Settings
The MT2834MR has three two-position jumpers (one for each modem)
for OOS and service. Each set of OOS jumpers defines pin 25 of the
RS232C/D interface as an input (OOS) or an output (Test Mode) for
one of the three modems. Each is set to a default of OOS (U.S.);
international models have a default setting of Test Mode.
There is also a factory-set selection for MI/MIC (modified dial-up
phone line interface that allows dialing by an external device such as an
801 Dialer, computer or PBX/CBX system dialer).
7.4.1 ATEST/AV54 Jumper (S105)
Jumper S105 sets pin 25 of Modem A as input (OOS) for the default
and output (Test Mode) as the option setting on domestic (US)
modems. On international modems, Jumper S105 sets pin 25 of Modem
A as input (OOS) for the option, and output (Test Mode) as the default
setting.
7.4.2 BTEST/BV54 Jumper (S205)
Jumper S205 sets pin 25 of Modem B as input (OOS) for the default
and output (Test Mode) as the option setting on domestic (US)
modems. On international modems, Jumper S205 sets pin 25 of Modem
B as input (OOS) for the option, and output (Test Mode) as the default
setting.
7.4.3 CTEST/CV54 Jumper (S305)
Jumper S305 sets pin 25 of Modem C as input (OOS) for the default
and output (Test Mode) as the option setting on domestic (US)
modems. On international modems, Jumper S305 sets pin 25 of Modem
C as input (OOS) for the option, and output (Test Mode) as the default
setting.
Appendix B
Dial Pulse and Tone-Dial Frequencies
DIAL PULSES
If the digit 2 is pulse dialed, followed by the digit
1. Each pulse consists of an A mSec. open and a B mSec. closed, where
A will be either 60 or 67 mSec and B will be either 40 or 33 mSec., for
a total of 100 mSec. per pulse, or a rate of 10 pulses per second. The
interdigital pause time is 800 mSec. The pulse ratios are controlled by
the &P command*.
TONE DIAL FREQUENCIES
The tone-dialing method combines two frequencies for each of the
twelve digits found on a Touch Tone dial pad. This method is referred
to as Dual-Tone Multi-Frequency (DTMF) dialing.
The four horizontal rows on a Touch-Tone keypad use the four low
frequencies (697, 770, 852, 941 Hz), while the three vertical columns
use the three high frequencies (1209, 1336, 1477 Hz). The generally
accepted tone frequency tolerance is +0.02%.
*Not applicable in BABT models
For example, the digit 4 would be dialed by combining two tone
frequencies. It would use the frequency 770 Hz from the second row,
and the frequency 1209 Hz from the first column. In another example,
the digit 9 would be dialed with the tone frequencies of 852 Hz and
1477 Hz.
The extended DTMF characters (A, B, C, D) are the high-end
frequencies (1633 Hz) defined on some telephone sets with a fourth
vertical column of buttons. This fourth column provides for extended
PBX control functions; the actual functions provided are dependent on
the PBX manaufacturer's implementation and feature set.
Appendix C
DIP-Switch Summary
DIP-Switch Condition Effect
Asynchronous Mode
#1 *UP DTR dependent on interface
Down DTR force On at all times
#2 *UP Hardware Flow Control
Down Xon/Xoff Flow Control
#3 UP Disable Command Mode Response
(dial up)
*Down Enable Command Mode Response
(dial up)
#3 UP -10 dB Transmission (leased line)
*Down 0 dB Transmission (leased line)
Note: dB transmission levels on International models may be different
from those values shown above.
Note: Switch #3 has no effect in leased line mode in the MT2834MRK.
#4 *UP UUCP Spoofing Disabled
Down UUCP Spoofing Enabled
#5 *UP Enable Automatic Answer (dial up)
Down Disable Automatic Answer (dial up)
#5 *UP Answer Mode (leased line)
Down Originate Mode (leased line)
#6 *UP Max throughput Enabled
Down Max throughput Disabled
#7 UP RTS dependent on Interface
*Down RTS forced On at all times
#8 UP Disable Command Mode
*Down Enable Command Mode
#9 UP No function
*Down
#10 *UP Dial-Up Operation
Down Leased Line Operation
#11 UP "AT" Responses
*Down Multi-Tech Responses
#12 UP Synchronous Mode
*Down Asynchronous Mode
See page C-3 for information on DIP-Switches #13 - #16
DIP-Switch Condition Effect
Synchronous Mode
#1 *UP DTR Dependent On interface
Down DTR forced On at all times
#2 *UP SDLC Mode On
Down BSC Mode On
#3 UP Disable Command Mode Response
(dial up)
*Down Enable Command Mode Response
(dial up)
#3 UP -10 dB Transmission (leased line)
*Down 0 dB Transmission (leased line)
Note: dB transmission levels on International models may be different
from those values shown above.
Note: Switch #3 has no effect in leased line mode in the MT2834MRK.
#4 *UP AS/400 Mode Disabled
Down AS/400 Enabled
#5 *UP Enable Automatic Answer (dial up)
Down Disable Automatic Answer (dial up)
#5 *UP Answer Mode (leased line)
Down Originate Mode (leased line)
#6 *UP Slave Clocking Disabled
Down Slave Clocking Enabled
#7 UP RTS Dependent on interface
*Down RTS Forced On at all times
#8 UP Disable Command Mode
*Down Enable Command Mode
#9 UP No function
*Down
#10 *UP Dial-Up Operation
Down Leased Line Operation
#11 UP External Clock
*Down Internal Clock
#12 UP Synchronous Mode
*Down Asynchronous Mode
Appendix D
Result Code Summary
DIGIT WORDS EFFECT
"Multi-Tech" Result Codes*
0 OK Command was executed without
error; ready for next command.
1 CONNECT Modem has detected carrier and gone on-line.
2 RING Modem has detected ring caused by
incoming call.
3 NO CARRIER No carrier signal has been detected within allowed
time.
4 ERROR Error in Command line (too many, or invalid
characters).
5 CONNECT 1200 Modem has detected carrier at 1200 bps and gone
on-line.
6 NO DIAL TONE No dial tone has been detected.
7 BUSY A busy signal has been detected.
8 NO ANSWER Remote system did not answer.
9 CONNECT 2400 Modem has detected carrier at 2400 bps and gone
on-line.
11 CONNECT 4800 Modem has detected carrier at 4800 bps and gone
on-line.
12 CONNECT 9600 Modem has detected carrier at 9600 bps and gone
on-line.
13 CONNECT 14400 Modem has detected carrier at 14400 bps and gone
on-line.
19 CONNECT 19200 Modem has detected carrier at 19200 bps and gone
on-line.
21 CONNECT 21600 Modem has detected carrier at 21600 bps and gone
on-line.
23 CONNECT 1275 Modem is connected in V.23 mode.
24 CONNECT 24000 Modem has detected carrier at 24000 bps and gone
on-line.
26 CONNECT 26400 Modem has detected carrier at 26400 bps and gone
on-line.
28 CONNECT 28800 Modem has detected carrier at 28800 bps and gone
on-line.
Note: If the MT2834MR is used in MNP Reliable mode, the following
Result Codes change:
1R CONNECT RELIABLE
5R CONNECT 1200 RELIABLE
9R CONNECT 2400 RELIABLE
11R CONNECT 4800 RELIABLE
12R CONNECT 9600 RELIABLE
13R CONNECT 14400 RELIABLE
19R CONNECT 19200 RELIABLE
21R CONNECT 21600 RELIABLE
24R CONNECT 24000 RELIABLE
26R CONNECT 26400 RELIABLE
28R CONNECT 28800 RELIABLE
*See Note 2 for "AT Command Set Result Codes".
Note: If the MT2834MR used in LAP-M Reliable mode, the following
Result Codes change:
1L Connect LAPM
5L Connect 1200 LAPM
9L Connect 2400 LAPM
10L Connect 4800 LAPM
12L Connect 9600 LAPM
13L Connect 14400 LAPM
19L CONNECT 19200 LAPM
21L CONNECT 21600 LAPM
24L CONNECT 24000 LAPM
26L CONNECT 26400 LAPM
28L CONNECT 28800 LAPM
Note 1: If the MT2834MR is used with data compression, the word
COMPRESSED or the letter C is added to the result codes.
Note 2: If Standard AT Command Set 2400 Result Codes are selected
with &Q command, the following Result Codes change:
9 (not used)
10 CONNECT 2400 Modem has detected carrier at 2400
bps and gone on-line.
Appendix E
S-Register Summary
REGISTER UNIT RANGE DEFAULT DESCRIPTION
S0 1 ring 0-255 1 Sets number of rings until
modem answers.
S1 1 ring 0-255 0 Counts rings which have
occurred.
S2 ASCII 0-127 43 Sets Escape Code character
(default is plus + sign).
S3 ASCII 0-127 13 Sets character recognized as
RETURN (default is CTRL-M).
S4 ASCII 0-127 10 Sets character recognized
as LINE FEED (default is CTRL-J).
S5 ASCII 0-32 8 Sets character recognized as
127 BACKSPACE (default is CTRL-H).
S6 1 sec. 2-255 2 Defines wait-time for dial tone.
4-7* 4*
S7 1 sec. 1-255 45 Defines how long modem
1-45* will wait for carrier before
aborting call.
S8 1 sec. 0-255 2 Sets pause time caused by a
4-7* 4* comma character in a dial
command.
S9 100mSec 1-255 6 Sets Carrier Detect response time.
S10 100mSec 1-255 7 Sets delay time between when
carrier is lost and when modem
disconnects.
S11 1 mSec 1-255 70 Sets time duration of and
80-255* 80* spacing between tones in
tone-dialing.
S13 ASCII 0-127 37 Defines Remote Configuration
Escape Character
S17 10mSec 0-2500 250mSec Defines length of break time seconds
(space) to PC.
S18 30 min. 10-255 30 Modem monitors leased line to
see if it's
operational and will try
to restore leased line connection.
S19 1 min 0-255 1 Dial-backup timer used for
timing dial-line back-up.
S24 50 mSec 0-255 20 Sets DSR/CTS/CD dropout
time. The default (20) equals
one second.
S25 100mSec 0-255 0 Sets DTR dropout time.
The default (0) default equals 50
mSec.
S30 min 0-255 0 Inactivity timer used to disconnect
modem.
S32 1 sec. 0-255 2 mSec S32 sets the time that the
modem waits for <CR> to be
entered during Escape Sequence
execution.
S34 ASCII 0-60 10 Sets the number of command
characters allowed for Escape
Sequence entry.
S36 1 sec 0-255 0 When DTR is low for S36
seconds, the modem sets OOS.
S37 1 sec 5-255 5 When DTR is high for S37
seconds, the modem clears OOS.
* Values for MT2834MRK units only.
Appendix F
Command Summary
COMMAND VALUES DESCRIPTION
AT Attention Code that precedes most command
strings except A/, A: and Escape Codes.
RETURN Pressing RETURN key executes most commands.
A Answer call, even if no ring present.
A/ Repeat last command. Do not precede this
command with AT. Do not hit ENTER to execute.
&A Answerback (proprietary feature)
A:** Continuous redial (10 redials in DOC units)
of last number until answered.
$An n = 0 or 1 ***$A0 discards data during auto-reliable time
period.
$A1 buffers data during auto-reliable time
period.
#An n = 0 thru 3 ***#A0 selects initial handshake at 28,800 to
24,000 to 21,600 to 19,200 to 16,800 to
14,400 to 12,000 to 9600 to 4800 to 2400 to
1200 to 300 bps.
#A1 selects initail handshake at 28,800 bps
only.
#A2 selects initail handshake at 28,800 to
24,000 to 21,600 to 19,200 to 14,400 to
9600 to 4800 bps only.
#A3 selects initial handshake at 2400 to
1200 to 300 bps only.
%ASn n = 0 or 1 ***%AS0 disables IBM AS/400 Support
%AS1 enables IBM AS/400 Support
Bn** n = 0 or 1 B0 selects ITU-T answer tone at 300 baud.
***B1 selects Bell answer tone at 300 baud.
&Bn n = 0 or 1 ***&B0 means normal transmit buffer size.
&B1 means reduced transmit buffer size.
&BSn n = 0 or 1 &BS0 means maximum transmit block size of
64 characters.
***&BS1 means maximum transmit block size of
256 characters.
$BAn n = 0 or 1 ***$BA0 means Baud Adjust is off, speed conversion is on.
$BA1 means Baud Adjust is on, speed conversion is off.
&Cn n = 0, 1, &C0 forces Carrier Detect on.
2, or 4 ***&C1 lets Carrier Detect act normally.
&C2 lets Carrier Detect drop S24 time on
disconnect.
&C4 resets modem when Carrier Detect drops.
*Cn n=0 thru 2 ****C0 turns off Caller ID detection
*C1 turns on Caller ID detection for the MMM
*C2 turns on Caller ID reporting on the
serial port by the MMM
Ds s = phone # Dial a telephone number "s," where s may
include up to 60 digits or T, P, R, comma
and ; characters.
DsDn s = phone # Store telephone number. To store, phone d = 0 thru 9
number "s" is entered and followed by N and then
Directory Number "d".
&Dn n = 0 thru 3 &D0 DTR is ignored
&D1 means modem returns to command mode.
***&D2 lets modem react to DTR normally.
&D3 causes modem to reset to modem
default parameters.
$Dn n = 0 or 1 ***$D0 disables DTR Dialing.
$D1 enables DTR Dialing.
En n = 0 or 1 E0 means do not echo Command Mode Character.
***E1 means do echo Command Mode Characters.
$En n = 0 or 1 ***$E0 disables 300 baud error correction.
$E1 enables 300 baud error correction.
&En n = 0 thru 15 &E0 means V.42 Normal Mode.
***&E1 means V.42 Auto-reliable Mode.
&E2 means V.42 Reliable Mode.
&E3 means no modem-initiated flow control.
***&E4 means CTS modem-initiated flow control.
&E5 means Xon/Xoff modem-initiated flow
control.
***&E6 means Xon/Xoff not passed through.
&E7 means Xon/Xoff passed through.
***&E8 means Enq/Ack pacing off.
&E9 means Enq/Ack pacing on.
***&E10 means Normal Mode flow control off.
&E11 means Normal Mode flow control on.
&E12 means Pacing off.
***&E13 means Pacing on.
&E14 means data compression disabled.
***&E15 means data compression enabled.
$EBn n = 0 or 1 ***$EB0 enables 10 bit mode.
$EB1 enables 11 bit mode.
%En n=0 thru 5 % E0 = Modem Won't Escape.
***% E1 = +++ Method (default setting).
% E2 = Break Method.
% E3 = Either +++ or Break Method.
***% E4 = Disables "OK" Response to +++
Escape Method.
% E5 = Enables "OK" Response to +++
Escape Method.
#Fn n = 0, 1, 8, #F0 means no fallback when on-line.
or 9 #F1 means fallback from 14400 to 4800 bps
when on-line.
***#F2 means fallback to 4800 bps from
14.4K/fall forward when line improves.
&F &F loads factory default values from ROM.
***&F8 loads factory defaults after &F.
&F9 loads RAM defaults after &F.
$Fn n = 0 or 1 $F0 means do not fall back to normal
connect if CR received.
***$F1 means fall back to normal connect if CR
received.
&Gn** n = 0, 1 or 2***&G0 turns off ITU-T guard tones.
&G1 turns on ITU-T 550 Hz guard tone.
&G2 turns on ITU-T 1800 Hz guard tone.
Hn n = 0 or 1 H0 means Hang Up (go on hook).
H1 means Go Off Hook.
$Hn n = 1 thru 3 $H1 brings up Help Screen #1.
$H2 brings up Help Screen #2.
$H3 brings up Help Screen #3.
In n = 0 or 1 I0 requests modem ID #.
I1 requests firmware revision #.
L Lists all stored telephone numbers in memory.
L5 L5 lists all current operating parameters.
L6 L6 lists all current S-Register values.
L7 L7 lists additional parameters.
L8 L8 lists on-line diagnostics
#Ln n = 0 thru 3 ***#L0 means modems negotiate V.42 Mode.
#L1 means MNP on and LAP-M off.
#L2 means LAP-M on and MNP off.
#L3 means no detection phase but go
directly to LAP-M.
&Ln n = 0,1,2A, &L0 selects Dial-up line operation
2D,4A,4D &L1 allows a single attempt at
leased line connection
&L2A selects 2 wire Answer mode operation
&L2D selects 2 wire Originate mode operation
&L4A selects 4 wire Answer mode operation
&L4D selects 4 wire Originate mode operation
&Mn n = 0 or 1 ***&M0 means Async when on-line.
&M1 means Sync when on-line.
$MIn** n = 0 or 1 ***$MI0 disables MI/MIC option (**)
$MI1 enables MI/MIC option (**)
$MBn n = speed $MB75 selects ITU-T V.23 mode.
$MB300 selects 300 bps on-line.
$MB1200 selects 1200 bps on-line.
$MB2400 selects 2400 bps on-line.
$MB4800 selects 4800 bps on-line.
$MB9600 selects 9600 bps on-line.
$MB14400 selects 14400 bps on-line.
$MB19200 selects 19200 bps on-line.
$MB24000 selects 24000 bps on-line.
***$MB28800 selects 28800 bps on-line.
Nd d = 0 thru 9 Dial stored telephone number "d".
Do not include the letter D with this command.
NdNe d = 0 thru 9 Number Linking. If first number dialed is
e = any other busy, another stored number may be number
number 0 automatically dialed. For example, stored
thru 9 number "d" is dialed, and if busy, stored
number "e" is dialed.
O Exit Command Mode and go into On-Line Mode.
P ***Modem will pulse-dial numbers following the P.
&Pn** n = 0 or 1 ***&P0 means 60-40 pulse ratio.
&P1 means 67-33 pulse ratio.
#Pn n=0 thru 2 ***#P0 means no parity.
#P1 means odd parity.
#P2 means even parity.
Qn n = 0 or 1 ***Q0 means Result Codes sent.
Q1 means Result Codes will be suppressed
(quiet).
Q2 means Dumb Answer Mode.
&Qn n = 0 or 1 ***&Q0 selects Multi-Tech command set.
&Q1 selects AT command set.
Rn n = 0 or 1 ***R0 means modem will not reverse modes.
R1 means modem will reverse modes.
&Rn n = 0, 1 or 2 &R0 lets Clear to Send act normally.
***&R1 forces Clear to Send on.
&R2 drops for 1 second on disconnect.
&RFn n = 0 or 1 &RF0 selects CTS follows RTS.
***&RF1 selects CTS to act independently.
$Rn n = 0 or 1 ***$R0 means disconnect after 12 retransmits.
$R1 means do not disconnect after 12
retransmits.
Sr=n r = 0 thru 11, Sets value of Register "r" to value of "n",
13, 17-19, 24, where "n" is entered in Decimal format.
25, 30, 32, 34
Sr? r = 0 thru 11, Reads value of Register "r" and displays
13, 17-19, 24, value in 3-digit Decimal format.
25, 30, 32, 34
$SBn n = speed $SB1200 selects 1200 bps at serial port.
$SB2400 selects 2400 bps at serial port.
$SB4800 selects 4800 bps at serial port.
$SB9600 selects 9600 bps at serial port.
$SB19200 selects 19,200 bps at serial port.
$SB38400 selects 38,400 bps at serial port
$SB57600 selects 57600 bps at serial port.
***$SB115200 selects 115200 bps at serial port.
&Sn n = 0, 1 or 2 &S0 forces Data Set Ready On.
***&S1 lets Data Set Ready act normally.
&S2 Data Set Ready drop is regulated by
S24 on disconnect.
&SFn n = 0 or 1 ***&SF0 selects DSR follows CD.
&SF1 selects DSR independent.
$SPn n = 0 or 1 ***$SP0 disables UUCP Spoofing
$SP1 enables UUCP Spoofing
T Modem will tone-dial numbers following the T.
&Tn n = 4 or 5 &T4 means Enable Response to Request for
Remote Digital Loopback.
***&T5 means Disable Response to Request for
Remote Digital Loopback.
#Tn n = 0 or 1 #T0 turns off Trellis Coded Modulation
***#T1 turns on Trellis Coded Modulation
Un n = 0, 1, 2, U0 places modem in Analog Loop Originate
or 3 Test Mode.
U1 places modem in Analog Loop Answer
Test Mode.
U2 places modem in Remote Digital Loopback
Test Mode.
U3 places modem in Local Digital Loopback
Test Mode.
Vn n = 0 or 1 V0 means Result Codes sent as digits
(terse response).
***V1 means Result Codes sent as words
(verbose response).
W Wait for new dial-tone.
&Wn n = 0 or 1 &W0 causes modem to store its current
parameters in non-volatile RAM, and
modem loads these for future sessions
instead of reading factory ROM defaults,
unless &F command used.
***&W1 causes modem to not store parameters.
Xn n=0 thru 4 X0 selects Basic Result Codes w/o CONNECT 1200,
CONNECT 2400)
X1 selects Extended Result Codes
(w/ CONNECT 1200, CONNECT 2400)
X2 selects Standard AT command set with
NO DIAL TONE
X3 selects Standard AT command set with
BUSY
***X4 selects Standard AT command set with
NO DIAL TONE and BUSY
&Xn n = o thru 2 ***&X0 Sync internal clocking.
&X1 Sync external clocking.
&X2 Sync slave clocking.
#Xn n = 0 or 1 #X0 causes one XOFF to be sent until buffer
reaches XON level
#X1 causes one XOFF to be sent for every
character received after modem reaches
buffer full level
Yn n = 0 or 1 ***Y0 disables sending or responding to long
space "break".
Y1 enables sending or responding to long
space "breaks".
Z All configuration parameters are reset to
default values.
, in Dial Causes pause during dialing.
command
; in Dial Causes return to Command Mode after
command dialing.
! in Dial Causes modem to Flash On-Hook.
command
@ in Dial Causes modem to wait for ringback, then 5
command seconds of silence before processing
next part of command.
+++AT<CR> Escape Code. Puts modem in Command Mode while
remaining On-Line. Type +++ followed by the letters
A and T & up to ten command characters, and hit ENTER.
BREAK AT<CR> Alternate Escape Sequence. Brings modem into
Command mode while remaining On-Line. Not preceded
by AT. Type BREAK signal, followed by the letters
A and T, up to 60 command characters, and hit
ENTER.
Appendix G
V.25bis Operation
Operation of your modem in ITU-T V.25bis mode provides you with an
alternate set of commands and responses to those described in the AT
Command Mode chapter of this manual. The V.25bis mode performs
dialing functions in the asynchronous or synchronous mode according
to the recommendations of the ITU-T (Consultative Committee of
International Telephony and Telegraphy). Synchronous mode, which is
the more common use of V.25bis, includes both Binary Synchronous
Communications (BSC) and Synchronous Data Link Control (SDLC).*
V.25bis is commonly used in IBM (and other) mainframe and mid-
range (S/3x and AS/400) environments. The V.25bis mode commands
are used to establish data connections over public switched telephone
networks.
We've already covered the AT command set with its dialing features
earlier in this manual. The V.25bis commands can be looked at as a
second command set used to perform synchronous dialing functions,
and, since the AT command set cannot perform synchronous dialing, it
is necessary for dial-up synchronous applications.
V.25bis mode AT commands do not include any modem configuration
commands. You can execute normal AT commands in V.25bis mode
for modem configuration.
Delayed and Forbidden Numbers
V.25bis provides the facility to delay failed call retry attempts by
putting numbers that failed to connect on a special Delayed Number
list. Subsequent dialing of these numbers are delayed (time specified by
a country regulation) and an appropriate message displayed. If the
number is retried more than the maximum allowed number of times
(number is also specified by country regulation), it is placed on the
Forbidden Numbers list, and no further retries are allowed. When the
Forbidden Numbers list is full, no dialing is allowed and a CFIFF
indication is given. The modem in AT command mode responds with
NO CARRIER. If country regulations require that the Forbidden
Numbers list be checked in AT mode, then NO CARRIER is the
response to a dial attempt in AT mode. Numbers are also be put on the
Forbidden Numbers list if the Delayed Numbers list is full and a new
number fails for the first time. In that case, the new number is added to
the Delayed Number list and the oldest existing number added to the
Forbidden Numbers list. Numbers are removed from the Forbidden
Numbers list after a certain time has past (also by country regulation).
Some country regulations have numbers remain on the Forbidden
Numbers list permanently. The Delayed Number and Forbidden
Numbers lists are eight numbers long (20 characters each).
Operation
Operation in V.25bis mode is similar to AT command mode except that
certain DIP Switch functions are important to its operation. V.25bis
does not include any speed detection for asynchronous mode, so when
you are giving commands, you must stay in your initial speed (i.e., if
you change your terminal speed while entering an AT command, you
get no responses). In synchronous mode, the modem supplies the clock,
so the synchronous terminal "knows" the speed.
You must be in V.25bis mode for the commands described here to
function. Most AT commands also function, except those associated
with dialing such as ATD, ATN, ATO, and ATU. To get into V.25bis
mode, type AT$V1. At this point your modem does no more speed or
parity detection (things associated with asynchronous operation). To get
out of V.25bis mode and back into AT command mode, type AT$VO.
The AT$V2 command allows you to run one V.25bis command from
AT command mode without leaving AT command mode.
There is no command to select between asynchronous and synchronous
V.25bis operation. The position of 4-Position DIP-Switch #4 selects
modes. For synchronous mode, thesynchronous switch must be on, the
command mode enabled and a jumper plug selects between BSC and
SDLC.
Another asynchronous mode issue is connecting at a different speed
than the speed at which the serial port is set. If your modem port speed
is different from the serial port speed, you must either:
1. Enable speed conversion and have flow control on, or
2. Enable connect responses (with the ATX1 command)
and change the serial baud rate after receiving a connect message.
DTR dialing is functional in V.25bis mode, except the number dialed is
from the V.25bis mm memory location 01. Also, if the $VD1 command
is entered when in Auto-Answer mode, the modem answers
immediately upon receiving the first ring.
There is no disconnect message (NO CARRIER) if a normal connection
is made.
Set-Up and Initialization
Before you operate your modem in the V.25bis mode, you need to
make sure it is set-up properly (various RS232 lines such as DSR and
CTS act as specified in the V.25bis standard). Set-up involves proper
DIP-Switch settings, and soft-switches (software controlled conditions).
V.25bis DIP-Switches
12-Position DIP-Switches
#1 - Unforced DTR
#2 - NA
#3 - NA
#4 - NA
#5 - Auto-Answer enabled
#6 - DSR/CD unforced
#7 - RTS unforced
#8 - Command Mode forced
#9 - NA
#10 - NA
#11 - NA
#12 - NA
4-Position DIP Switches
#1 - Unforced CTS
#2 - Dial-Up
#3 - Varies per modem model
#4 - Async/Sync mode set per requirements
Jumper Plugs
CTS/RTS - CTS independent of RTS
DSR - DSR independent of CD
MI/MIC - NA
SLDC/BSC - If in Synchronous mode, set per requirements.
V.25bis Mode AT Commands
The following commands either alter standard V.25bis behavior (so you
must be careful in their use) or they are not allowed, as indicated. All
other commands can be used in V.25bis operation.
A Not Allowed
A/ Not Allowed
A: Not Allowed
D Not Allowed
D...N Not Allowed
$D Alters Operation ($D1 in V25bis is direct
call mode)
E Alters Operation
&F Alters Operation (removes modem from
asynchronous V.25bis mode)
N Not Allowed
N...N Not Allowed
O Not Allowed
P Not Allowed
T Not Allowed
U Not Allowed
W Not Allowed
X Alters Operation (X0 no connect message)
(X1 connect message)
, Not Allowed
; Not Allowed
! Not Allowed
@ Not Allowed
+++AT<CR> Not Allowed
V.25bis Responses (Result Codes)
When in V.25bis mode (the AT$V1 command executed), your modem
provides you with several responses which helps you follow the
progress of V.25bis operations. These are similar to the Result Codes
associated with AT Command mode operation. The V.25bis responses
are in the form of three-character mnemonics as listed on the next page:
INC Incoming Call (same as RING indicator)
VAL A valid V.25bis command has been attempted
DLCt Call delayed for t minutes (number on Delayed list)
CFlrr Call failure indicator where rr equals:
et - Engaged tone (same as BUSY)
nt - Call Answered but No Answer Tone
ab - Call Not Answered
fc - Number on Forbidden List
ns - Number not stored in memory
ua - User Abort
nd - No Dialtone
ff - Forbidden List full
LSNmm;dd...dd Phone number in V.25bis memory
LSDmm;dd...dd Phone number on the Delay list
LSFmm;dd...dd Phone number on the forbidden list
CON ssss Connection at ssss speed (if X1 in effect)
V.25bis AT Commands
The AT commands associated with V.25bis mode are described as
follows. Note that one command enables and disables V.25bis mode
and the rest are only operable in the V.25bis mode.
Enable/Disable V.25bis Mode ($V) Command
The function of the $V command is to select the V.25bis mode in
asynchronous mode. (Synchronous mode is set up with switches. For
example, the modem could be in AT command mode, (AT$V1), and if
synchronous mode is enabled with AT Command mode enabled, then
V.25bis mode is selected). Prior to executing this command, make sure
that your modem is properly set up to perform the type of operation you
are performing. Refer to the initialization section of this appendix for
information about modem set-up. When in V.25bis mode, most normal
AT commands also function (except D,N,O and U). V.25bis operates
in asynchronous or synchronous modes (depending on the position of
4-Position DIP-Switch #4), and does not check for terminal speed (so
do not change speeds while in this mode) or parity. In synchronous
mode, speed is not important since the internal clocks provide
synchronization.
To place your modem in V.25bis mode from asynchronous mode, enter
the AT$V1 command. To return to AT command mode, enter the
AT$V0 command. AT$V2 allows you to run one V.25bis command
from AT command mode without leaving AT command mode (the
V.25bis command follows $V2 on the command line).
Clear Number in Memory (CLA) Command
The CLA command clears a specific number in the mm phone number
memory by entering CLAmm.
Change Serial Baud Rate (CSP) Command
The CSP command changes the serial baud rate of your modem by
entering CSPsssss where sssss can equal:
0300 = 300 bps
1200 = 1200 bps
2400 = 2400 bps
4800 = 4800 bps
9600 = 9600 bps
19200 = 19200 bps
38400 = 38400 bps
57600 = 57600 bps
115200 = 115200 bps
Dial Phone Number Provided (CRN) Command
The CRN command permits the dialing of the phone number
immediately following it (from the command line). It is similar to the D
command of the AT command set, except that the number is first
checked against the Delayed Number and Forbidden Number list. If
permitted, depending on the country regulations in effect, the number is
then dialed. For example, if you type CRN7859875 and hit ENTER,
your modem checks the two lists. If the number is on the Delayed
Numbers list, you can dial that number again after t minutes have
passed. If the number is on the Forbidden list, a CFIFC message is
displayed.
You can use various commands from the AT command set within the
CRN command line to facilitate the dialing process, such as P, T, or W
for pulse dialing, tone dialing and wait for dial tone. V.25bis supports
"smart" dialing.
To dial a phone number, type CRNdd...dd where dd...dd is the phone
number, which can be up to 20 characters long using any character on
the telephone pad (0 through 9, *, #, P, T, and :).
Some additional dialing characters may be available, based on country
regulations.
Dial Phone Number Stored in Memory (CRS) Command
A telephone number that you have stored in the modem's memory may
be automatically dialed after checking it against the Delayed and
Forbidden number lists by entering CRSmm where mm = 01, 02, 03,
04,....20. For example, a number stored in mm location 15 is entered
CRS15 and hitting ENTER, then, if the number in mm memory location
15 is not on either list, it is automatically dialed.
Store a Phone Number in Memory (PRN) Command
Your modem has a special V.25bis memory for storing phone numbers
which you may dial by using the CRS command. The memory holds up
to 20 numbers of 20 characters each. You can store phone numbers in
this memory with the PRN command. The format for the command is
PRNmm;dd...dd where mm is the memory location at which you wish to
store a number (any digits 01 through 20) followed by a semicolon(;)
and then dd...dd (the number to be stored up to 20 digits long). The
number can include punctuation as required.
To clear a number from the V.25bis memory, see the CLA command.
Listing Numbers Stored in Memory (RLN) Command
Telephone numbers that you have stored in the modem's V.25bis
memory may be listed and displayed with the RLN command. It
displays all twenty mm storage location numbers and associated
telephone numbers with any command letters and punctuation
imbedded in each number. The RLN command is similar to the L
command of the AT command set. To list the V.25bis stored telephone
numbers, type RLN and hit ENTER.
Listing Delayed Phone Numbers (RLD) Command
When a phone number is dialed either by a CRN or CRS command and
a connection is not made, the number is entered in the modem's V.25bis
Delayed Number list along with the number of retry attempts. Any
further dialing attempts is delayed some amount of time (determined by
the regulations of each country). While the delay is in progress, the
modem gives a DLC indication. The list contains eight numbers. When
filled, the next number failing "bumps" off the oldest number on the list
onto the Forbidden Number list. Numbers on the Delayed Number list
that succeed in a connect attempt are removed. If a certain number of
failed attempts occur (the number of failed attempts is specified by each
country), the number is entered into the V.25bis Forbidden Phone
Number List. Forbidden phone numbers cannot be dialed at all. To list
the phone numbers on the V.25bis Delayed Phone Number List, type
RLD and hit ENTER.
Listing Forbidden Phone Number (RLF) Command
Those phone numbers that have failed to connect the required number
of times as specified by country regulations are removed from the
Delayed Number list and entered onto the V.25bis Forbidden Number
list. Numbers on the Forbidden Number list cannot be dialed at all for
some maximum amount of time, which is also specified by country
regulations. In some countries, the time might be one hour, and in
others the number may never be dialed again. The forbidden list is eight
numbers long, with the newest number replacing the oldest if the
memory is full. To list the numbers in the Forbidden list type RLF and
hit ENTER.
Disregard or Connect to Incoming Calls (DIC or CIC) Command
The Disregard or Connect to Incoming Calls commands are used for
Auto-Answer operations. Depending on the country regulations, your
modem waits some amount of time or number of rings before answering
the call. During that time, you can stop the modem from answering the
call by entering the DIC (Disregard Incoming Calls) command. The
CIC (Connect to Incoming Calls) command causes your modem to
answer the call (either reversing the effect of a DIC command or simply
have your modem answer the call immediately without waiting the
regulation time before answering).
DTR Dialing ($D) Command
DTR Dialing is an alternate method of causing the modem to
automatically dial a number. Data Terminal Ready (DTR) is a signal
that comes into the modem from the terminal or computer to which it is
connected via pin 20 of the RS232 interface. In DTR Dialing, the
modem dials a stored number as soon as it receives a high DTR signal.
The DTR Dialing method is popular when using the modem in
synchronous applications.
To activate DTR Dialing, type the command AT$D1 and hit ENTER.
The modem now dials the phone number stored as N0 when it receives
a high DTR signal (see the D...N command in Chapter 4). DTR must
remain high for the duration of the call, until disconnect. To deactivate
DTR Dialing, type the command AT$D0 (or AT$D) and hit ENTER.
When you use DTR Dialing, be sure that DIP-Switch #1 is in the UP
position, so that DTR is not forced on.
In addition, when using DTR Dialing in a synchronous application, be
sure that DIP-Switch #8 is in the UP position to disable V.25bis
Command Mode.
ITU-T V.25bis Country Specific Information
Due to the flexibility of the V.25bis standard, each country may
establish specific regulations governing the way operations are handled.
The purpose of this document is to detail each country's specific
regulations that affect operation of V.25bis in Multi-Tech modems.
1. Italy
a) Command/Indication modifications
1. Phone number indications include status;
ZPSTTT
a) Z - U, D, or F, for Unrestricted,
Delayed or Forbidden
b) P - Delay time if delayed
c) S - Number of retries so far
d) TTT - Interdiction time to further
attempts
2. Modify RLN command to allow memory
location parameter
a) RLNmm is now valid to list one
number in memory
3. PRN and CLA commands do not work on
active memory locations
a) Active number are ones who are on
the delay or forbidden lists
4. Added dialing digit '<' to indicate 2 second
pause
b) Delayed and Forbidden list behavior
1. 5 retries without delay
2. 2 minute delay between next 4 retries
3. After 9 retries the number is put on the
forbidden list
4. 120 minute timer is started on entry to delay
list
5. When it runs out, the number is removed
from whichever list it is on
c) Auto-Answer mode behavior
1. Auto-Answer in 5 seconds if no DIC
2. Get 10 seconds after DIC to enter CIC
3. If 10 seconds times out then no connection is
possible
2. Switzerland
a) Command/Indication modification
1. Modem must remain on-hook for 5 seconds
after disconnect
2. Modem must remain on-hook for 5 minutes
after 4 consecutive failed calls
3. If modem must remain on-hook, then it is
"paused"
4. If the modem is paused and a call is
attempted a PAU indication is given.
a) PAUt Modem is paused for t
minutes
b) Delayed and Forbidden list behavior
1. 2 minute delay between 4 retries
2. After 4 retries the number is put on the
forbidden list
3. The number remains on the forbidden list
forever
c) Auto-Answer behavior
1. Auto-Answer mode after 2 rings if no DIC
3. Austria
a) Command/Indication modification (none)
b) Delayed and Forbidden list behavior
1. No delay between retries
2. After 2 retries to numbers that answer, but
give no answer tone (CFINT), the number is put on the
forbidden list
3. After 10 retries with busy or no dialtone, the
number is put on the forbidden list
4. The number remains on the forbidden list
forever
5. Delayed and Forbidden Numbers lists are
checked when dialing in AT mode.
If dialing is not possible then NO CARRIER is the response.
c) Auto-Answer behavior
1. Auto-Answer in 5 seconds if no DIC
4. France
a) Command/Indication modification (none)
b) Delay and Forbidden list behavior
1. 2 min. delay after 1st call, 4 after 2nd, 6
after 3rd, etc.
2. After 5 retries, the number is put on the
forbidden list
3. The number remains on the forbidden list
forever
4. Delayed and Forbidden Numbers lists are
checked when dialing in AT command mode. If dialing is not possible
then No Carrier is the response.
c) Auto-Answer mode behavior
1. Auto-Answer in 5 seconds if no DIC
5. Belgium
a) Command/Indication modification (none)
b) Delay and Forbidden list behavior
1. 1 min. delay between calls
2. After 4 retries, the number is put on the
forbidden list
3. The number remains on the forbidden list for
1 hour after entry to forbidden list
4. Delayed and Forbidden Numbers lists are
checked when dialing in AT command mode. If dialing is
not possible then No Carrier is the response.
c) Auto-Answer behavior
1. Auto-Answer in 5 seconds if no DIC.
6. Singapore
a) Command/indication modifications
1. Dialing digit '=' means wait for dialtone (acts
the same as ':' in dialing string).
b) Delay and Forbidden list behavior
1. 5 retries without delay
2. 2 minute delay between next 4 retries
3. After 9 retries the number is put on the
forbidden list
4. 120 minute timer is started on entry to delay
list
5. When it runs out, the number is removed from
whichever list it is on.
Appendix H
RS232C Interface Specifications
The MT2834MR's RS232C interface circuits have been designed to
meet the electrical specifications given in EIA (Electronic Industries
Association) RS232C standards. All signals generated by the modem
are approximately 10 volts when measured across a load of 3000 ohms
or greater. The receiving circuits of the modem accepts signals in the 3
to 25 volt range. The voltage thresholds are:
Negative = voltage more negative than 3 volts with respect to
signal ground
Positive = voltage more positive than +3 volts with respect to
signal ground
SIGNAL INFORMATION: NEGATIVE POSITIVE
Binary State One Zero
Signal Condition Mark Space
Control and Timing Function Off On
The input impedances of all modem circuits which accept signals from
the data processing terminal or CPU equipment have DC resistances of
4.7K. For more specific details, consult the EIA RS232C standard
itself.
The following chart lists the EIA RS232C interface pins and circuits
present on the MT2834MR's RS232C Interface connector. All other
pins are unused.
Pin Multi-Tech EIA Signal Circuit
Assign. Designation Circuit Source* Function
1 PG _ _ Protective Ground
2 SD BA DTE Transmitted Data
3 RD BB DCE Received Data
4 RTS CA DTE Request to Send
5 CTS CB DCE Clear to Send
6 DSR CC DCE Data Set Ready
7 SG AB _ Signal Ground
8 CD CF DCE Data Carrier Detector
9 +V +V DCE Test Voltage
12 HS -- DCE High Speed
15 TC DB DCE Transmit Clock
17 RC DD DCE Receive Clock
20 TR CD DTE Data Terminal Ready
22 RI CE DCE Ring Indicator
24 XTC DA DTE External Transmit Clock
25 OOS CN DTE Terminal Busy
* DTE = Data Terminal Equipment (terminal or computer)
DCE = Data Communications Equipment (the modem)
The computer or terminal should be supplied with a cable terminated
with a Cinch DB25P (or equivalent) connector mounted in a Cinch
DB51226-1 (or equivalent) hood assembly as specified by the EIA
RS232C standard.
FUNCTIONAL DESCRIPTION OF MT2834MR RS232C SIGNALS:
Transmitted Data - Pin 2, SD (BA)
Direction: to modem
Signals on this circuit are generated by the customer's terminal and
transferred to the transmitter of the MT2834MR. A positive signal is a
space (binary 0) and a negative signal is a mark (binary 0). The
transmitting terminal should hold this line in the marking state when no
data is being transmitted, including intervals between characters or
words. The TRANSMIT (SD) LED indicates the status of this circuit.
Received Data - Pin 3, RD (BB)
Direction: from modem
The lead is the data output of the modem. Data signals received from
the remote modem are presented on this line. When no carrier signal is
received (pin 8 negative), this line is forced into a marking condition.
The RECEIVE (RD) LED indicates the status of this signal.
Request To Send - Pin 4, RTS (CA)
Direction: to modem
The RTS signal indicates to the modem that the computer or terminal
has data to transmit.
Clear To Send - Pin 5, CTS (CB)
Direction: from modem
The CTS line indicates to the terminal that the MT2834MR will
transmit any data present on the Transmit Data line (pin 2).
Data Set Ready - Pin 6, DSR (CC)
Direction: from modem
DSR ON, indicates that the MT2834MR is in the data mode and is
connected to the communications channel. This signal is on during
analog-loop-test mode.
Signal Ground - Pin 7, SG (AB)
The SG lead is connected to signal ground of the modem. It establishes
the common ground reference for all other interface signals.
Data Carrier Detect - Pin 8, CD (CF)
Direction: from modem
DCD On (positive voltage) indicates that data carrier has been received
from the other modem. This circuit does not typically turn on in the
presence of message circuit noise or out-of-band signals. There is a one
second delay between when the carrier tone is detected and when the
CD circuit is turned on.
This signal goes off if received data carrier falls below the receiver
threshold for more than 37 mSec. When CD is off, the Received Data
circuit (pin 3) is held to the marking state.
Test Voltage - Pin 9, XV
Direction: from modem
The XV lead has 330 ohms of resistance to +12 volts DC. This lead
may be used to strap other signals high. For example, if the terminal
does not supply a DTR (Data Terminal Ready) signal, Pin 9 may be
jumpered to Pin 20 (DTR) on the RS232 connector or in the cable to
force DTR on.
High Speed - Pin 12, HS
The On condition of this circuit indicates that the modem is in the high
speed (1200 bps) mode. This circuit is commonly used to signal the
computer or terminal to which the modem is connected to switch to its
1200 bps setting.
Transmit Clock - Pin 15, TC (DB)
Direction: from modem
The TC signal is provided only when the MT2834MR is used in the
synchronous mode. The clock is a square wave and is used to provide
the computer or terminal with timing information for its Transmit Data
circuit (pin 2). This clock is provided on the interface at all times when
the modem is in synchronous mode.
The first signal element of the Transmitted Data signal should be
presented by the terminal on the first positive (Off to On) transition of
TC which occurs after the CTS circuit on pin 5 is turned on. The
transmitted data is sampled by the modem on negative transition of TC.
Receive Clock - Pin 17, RC (DD)
Direction: from modem
The RC signal has the same characteristic of Transmit Clock, with the
exception that it is used to provide the computer or terminal with timing
information for its Receive Data (pin 3) circuit. The negative transition
(On to Off) of RC indicates the center of each signal element on the
Received Data circuit.
Data Terminal Ready - Pin 20, TR or DTR (CD)
Direction: to modem
This signal (TR or DTR) provides a means for the terminal or computer
to control the modem's connection to the communications channel. A
high DTR signal is required by the modem to be able to communicate.
Turning DTR off for more than 50 mSec forces the modem to
disconnect.
The most common use of DTR is in automatic answer applications. A
high DTR signal is required by the modem to answer a call. A
frequently used method is to have the computer turn on DTR in
response to RI (Ring Indicator), which allows the modem to answer.
Later, DTR is turned off at the conclusion of the log off procedure,
which forces the modem to disconnect, enabling it to receive another
call. In non-auto answer applications it is advisable to leave DTR on
using the modem's DIP-Switch option. This is the standard factory
setting. An alternative is to provide a constant high DTR from the
terminal or computer. The Data Terminal Ready (DTR) LED indicates
the status of this signal.
Ring Indicator - Pin 22, RI (CE)
Direction: from modem
This signal remains on for the duration of the ringing signal. When a
ring signal is received by the modem, the modem automatically answers
after the first ring. The modem can answer after a specified number of
rings which can be programmed in AT Command Mode, but if none is
specified, the modem answers after the first ring.
External Transmit Clock - Pin 24, XTC
Direction: to modem
Supplies the same function as transmit clock on Pin 15.
Terminal Busy (Out of Service) - Pin 25, OOS
Direction: to modem
The Terminal Busy (OOS) circuit is not defined in the RS232C
standard, but is used by us and most manufacturers to make the phone
lines busy to incoming phone calls. Pin 25 is not typically connected to
the RS232C interface when shipped from the factory; it can be ordered
connected as an option. If pin 25 is connected and is brought high, the
modem is placed Off Hook, and is busy to incoming calls.
Appendix J
Multi-Tech SystemÆs Escape Methods
Introduction
You may find it necessary sometimes to issue AT commands to your
modem while you are on-line with a remote modem, without
disconnecting the call. If so, you will want to take advantage of Escape
methods which allow you to change the modem's mode of operation
from On-Line mode to Command mode, where you may issue AT
commands, without disconnecting. While you may then return on-line,
typically most users escape so that they may hang up a modem upon
completion of a call.
Our modems offer two Escape Methods: in-band, and out-of-band.
Both incorporate Time Independent Escape Sequence (TIES)
methodology. An escape sequence is a pattern, or sequence, that the
modem recognizes as its signal to shift from On-Line mode to
Command mode. Time Independent means that the modem recognizes
the escape sequence without a prefixed and/or suffixed delay.
In an in-band escape, the modem recognizes the escape sequence as a
pattern sent to it as part of the data stream or band (hence its name).
In an out-of-band escape, the escape sequence is a pattern that cannot
and does not occur in the data stream.
Our in-band escape method is: +++AT<CR>.
Our out-of-band escape method is: <BREAK>AT<CR>.
A BREAK signal cannot be sent as part of a data file; instead it is sent
by a direct program command to the UART used by that computer.
BREAK is defined as either the transmission of binary 0 for a minimum
of 10 bits; or as a minimum interval of 135 milliseconds as established
in the ITU-T X.28 standard. There are routines in high level languages,
and keys on most computers that have been established to send BREAK
for fixed intervals, but you may control the BREAK's duration by
refering to your UART's specifications.
How to Select an Escape Method
If you want your modem to escape and then wait for you to issue a
command before it will return to On-Line mode, then use +++AT<CR>.
You might use this method if you find you need to review a help screen
in the middle of a communications session.
If you wish to combine the escape with a command (or commands) and
with an immediate return to On-Line mode, then use the
<BREAK>AT<CR> method. You may also use this method to have
the modem wait before it will return On-Line.
You may select your modem's escape method by using an AT%E
command.
The AT commands used to select the modem's Escape Method are:
%E0 = Escape Disabled
%E1 = +++AT method (default)
%E2 = <BREAK>AT method
%E3 = Both escape methods enabled
%E4 = Disable OK response to +++
%E5 = Enable OK response to +++
Escape Method 1: +++AT<CR>
In the following example, a user who is On-Line decides to set S0
Register to 1, to configure the modem to answer on the first ring.
1. The user enters the sequence +++AT<CR> . The sequence
is sent to the modem.
2. The modem transmits the +++.
3. The modem buffers AT and starts the Wait for <CR> timer.
4. Upon receiving the <CR> the modem escapes to Command
mode.
5. The modem responds OK.
6. The user enters the command ATS0=1<CR>. This
sequence is sent to the modem.
7. The modem buffers ATS0=1<CR> and identifies it as a
valid command.
8. The modem executes the command, setting S0=1.
9. ATO<CR> is sent to the modem.
10. The modem returns to On-Line mode.
Escape Method 2: <BREAK>AT<CR>
In the following example, a user who is On-Line decides to set S-
Registers S0 to 1, to configure the modem to answer on the first ring.
1. The <BREAK> signal is sent to the modem.
2. The modem buffers <BREAK>.
3. The modem starts the S32 Wait for <CR> timer.
4. ATS0=1<CR> is sent to the modem.
5. The modem buffers ATS0=1<CR> and identifies it as a valid
command.
6. The modem escapes to Command mode.
7. The modem executes the command, setting S0=1.
8. The modem returns to On-Line mode.
S-Registers and Escape Sequences
There are two S-Registers that you may set to modify the functioning of
your escape sequences. The first is S-Register S32, which establishes a
value for how much time may elapse between the receipt of the
beginning of the escape sequence, whether <BREAK>AT, or +++AT,
and the receipt of a <CR>. This interval is known as Wait for <CR>
Time, or BREAK passthru.
You may assign a value to S32 in increments of 100 milliseconds. The
default value is 20, or 2 seconds.
In the +++AT<CR> method, the Wait for <CR> Time interval begins
once the A in +++AT is received by the modem.
In the <BREAK>AT method, the Wait for <CR> Time interval begins
once the modem has received the BREAK signal.
You may use S-Register S34 in conjunction with our in-band escape
sequence, +++AT<CR>, to establish the maximum number of
characters that your modem can buffer following an "AT," before a
<CR> must be received. The default value is 10 characters. Do not
confuse this buffer size with our regular Command mode buffer length
of 60 characters.
S-Register S34 does not affect our out-of-band escape sequence's buffer
length, which is fixed at 60 characters.
Aborting an Escape Sequence
The +++AT<CR> escape will abort if you do not issue a <CR> before
the Wait for <CR> Time interval expires.
The <BREAK>AT<CR> method will also abort if you do not issue a
<CR> before the Wait for <CR> Time interval expires, and also if any
of the following occurs:
1. An illegal sequence is detected, including:
a) A character other than A follows the <BREAK>;
b) A character other than T follows <BREAK>A;
c) Two BREAKS are received in succession;
2. The command buffer overflows before a <CR> occurs.
If you have any questions about the information contained in this
document, please direct them to:
Technical Support
c/o Multi-Tech Systems, Inc.
2205 Woodale Drive
Mounds View, Minnesota 55112 USA
Appendix K
Remote Configuration
Introduction
This chapter describes how the MT2834MR Remote Configuration
feature operates. This feature uses a multilevel security system that
involves the use of LOGIN passwords, SETUP passwords, and remote
escape characters.
The primary level security code is the modem's LOGIN password. Once
this password is entered, other passwords can be used. For instance,
entering the LOGIN password lets you enter the SETUP password.
The remote escape character is the key to using the Remote
Configuration feature. The remote escape character lets you enter
Command mode via a remote call, so that you can type AT commands
just as if you were locally connected. You must also type your modem's
SETUP password. The remote escape character is contained in S-
Register S13.
Remote Configuration Description
The Remote Configuration feature is a network management tool that
lets you configure modems remotely. This means you can configure
modems anywhere in your network from one location, without having
to visit the sites or rely on remote users to follow your instructions.
With Remote Configuration, which is protected by two-level security,
you can downline load new parameters, program new V.42 capabilities,
and implement new features. Remote Configuration also makes
troubleshooting remote locations a lot easier.
S-Register S13 contains the special remote configuration escape code.
When calling a Remote Configuration equipped modem, you enter the
proper remote escape code and SETUP password. After entering both
correctly, you can then execute AT commands as if you were connected
locally. If you set S-Register S13 to zero, Remote Configuration is
disabled.
Initial SETUP Procedures for Remote Configuration
Your modem is shipped with default LOGIN and SETUP passwords
(LOGIN=MULTI-TECH and SETUP=MODEMSETUP) so you can
configure the modem. Because the defaults are in the owner's manual,
anyone can find out what they are. You should change the codes as the
first step of your initialization procedure.
To change your modem's LOGIN and SETUP passwords, follow the
steps below.
NOTE: Passwords are upper/lower case sensitive. The case you
enter here is the case that must be used at login.
Modem LOGIN, SETUP, and Remote Escape Codes
1. Type AT#IMULTI-TECH and press ENTER. Your
modem responds with: OK (if the LOGIN password is wrong, the
modem's response is ERROR)
2. Type AT#SMODEMSETUP and press ENTER.
Your modem responds with the following: OK (or ERROR if the wrong
SETUP password is entered)
NOTE: At this point you can change the LOGIN password
and SETUP passwords.
3. Type AT#I=xxxxxxxxxx (with any keyboard
characters used: minimum = 6, maximum = 10) and press ENTER.
Your modem responds with: OK
4. Type AT#S=yyyyyyyyyy (with keyboard characters
used: minimum = 6, maximum = 10) and press ENTER. Your modem
responds with: OK
To change the status of your Remote Configuration feature:
5. To disable Remote Configuration, set S-Register S13
to 0 (zero). See Chapter 6 for details on how to set S-Register values.
6. To enable Remote Configuration and change the
remote escape character, type in a new S-Register S13 value.
Remote Configuration AT Commands
The following AT commands are used with the Remote Configuration
feature.
#I Modem LOGIN Password
The #I command lets you select a unique LOGIN password for your
modem. Once you have selected a LOGIN password for your modem, it
only responds to that code. Your modem is shipped with MULTI-
TECH as its default password so that you can gain access to the
command initially.
#S Modem SETUP Password
The #S command lets you select a unique SETUP password for your
modem. Once you have selected a SETUP password for your modem, it
only responds to that code. Your modem is shipped with
MODEMSETUP as its default password, so that you can gain access to
the command initially.
Remote Configuration S-Register
S-Register S13 is used with Remote Configuration. It defines the
MT2834MR remote configuration escape character. When the S13
character is entered three consecutive times from a remotely connected
site, your modem responds to it with its Remote Configuration
procedure. The default remote configuration escape character is the
"%" sign. See Chapter 4 for more information about this S-Register.
Remote Configuration Procedures
This section explains how to use the Remote Configuration feature;
they are the same whether or not a call originates from the remote
modem.
Remote Configuration Operation
1. Enter a break signal, then type the S13 remote
configuation escape character three times (the default S13 value is the
"%" sign). The modem responds with:
1. - DATA Mode
2. - COMMAND Mode
2. Select 1 or 2. With option 1, the modem goes back
into Data mode and with option 2, the modem responds with
Password>.
3. Type your SETUP password and, if the code is
correct, the modem responds with OK.
You can now use any AT commands remotely as if
they were entered locally. You cannot change the LOGIN password
until you enter the proper LOGIN password.
4. When you are done typing AT commands and you
wish to exit, type AT0 and press ENTER. The modem responds with:
1. DATA Mode
2. COMMAND Mode
5. Type 1 to go back on-line with your computer, or
type 2 and the correct password to talk to your modem.
