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CONNECT 26400 LAPM
26L
CONNECT 28800 LAPM
28L
CONNECT 31200 LAPM
31L
CONNECT 33600 LAPM
33L
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, 28,800, 31,200,
or 33,600 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”).
Содержание MT2834MR
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