Multi-Tech Systems MT2834MR6 manual Speed Conversion Commands

Chapter 3 - AT Commands

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	$MB300	300 bps
	$MB1200	1200 bps	$MB2400	2400 bps
	$MB4800	4800 bps	$MB7200	7200 bps
	$MB9600	9600 bps	$MB12000	12,000 bps
	$MB14400	14,400 bps	$MB16800	16,800 bps
	$MB19200	19,200 bps	$MB28800	28,800 bps
	$MB33600	33,600 bps (default)

45