Speed Conversion Commands - Multitech MultiModem MT2834MR6 User Manual

3.11 Speed Conversion Commands

Speed conversion allows the MT2834MR6 to communicate at a fixed speed through the serial port while
communicating at an independent speed over the online communications link. Speed conversion is
necessary for data compression, since data compression requires data to be sent from the computer to the
modem at a rate up to four times faster than the modem's transmission speed.
Speed conversion is also useful for an autoanswer modem connected to a computer that does not have
autobaud capability, since the computer must be set at a fixed baud rate regardless of the speed at which the
modem communicates over the phone line.
$BAn Baud Adjust
n = 0 or 1
Default: $BA0
Turning baud adjust off turns speed conversion on; turning baud adjust on turns speed
conversion off.
When baud adjust is on, the modem matches its RS-232 serial port speed to any changes
in the computer's serial port speed in originate mode, or to the speed of the originating
modem when it's in answer mode. With baud adjust on, the speed at which the modem
communicates over the phone line is always the same as the speed at which it
communicates via its RS-232 serial port.
When speed conversion is on, the modem does not adjust its speed at the serial port to
match its transmission speed. Serial port speed and transmission speed can therefore be
set independently. Speed conversion is necessary for a high speed modem that is
connected to a limited speed serial port.
$BA0 turns baud adjust off and speed conversion on.
$BA1 turns baud adjust on and speed conversion off.
$MBn Modem Baud Rate
n = speed in bits per second
Default: $MB33600
The $MB command sets a modem's initial transmission speed for originate mode. In V.32
mode (9600 bps), it also sets the transmission speed for answer mode. With speed
conversion on, this transmission speed can be different from the serial port speed.
When the modem answers a call from another modem, it automatically switches its
transmission speed to match the calling modem. However, if the MT2834MR6 originates a
call to another modem that is unable to connect at the same transmission speed, the
MT2834MR6 automatically drops to a lower speed in an attempt to match the speed of the
other modem.
Speed conversion must be on for this command to work. If baud adjust is on ($BA1), speed
conversion is off and a modem baud rate command will be ignored. The S48 register also
can affect maximum transmission speed. See Chapter 4.
$MB75 ITU-T V.23 mode
$MB1200 1200 bps
$MB4800 4800 bps
$MB9600 9600 bps
$MB14400 14,400 bps
$MB19200 19,200 bps
$MB33600 33,600 bps (default)
Chapter 3 - AT Commands
$MB300 300 bps
$MB2400 2400 bps
$MB7200 7200 bps
$MB12000 12,000 bps
$MB16800 16,800 bps
$MB28800 28,800 bps
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