Owner`s manual

PN 88300150
4/3/01 34
B Bell or ITU-T Tone
You can use the B command to select the frequency that the modem uses for its answer
tone. (The answer tone is the tone transmitted by a modem receiving a call to the modem
that called it, which initiates the handshaking between the two modems.) At higher speeds
(2400 to 14.4k bps) there is no conflict, because all use ITU-T frequencies. At lower speeds
(0-1200 bps), in the U.S., some modems use the Bell frequency of 2225 Hz. However, the
ITU-T specification for V.22bis has an answer tone frequency of 2100 Hz.
The ATB0 command enables the ITU-T answer tone. The ATB1 command enables the Bell
answer tone. The factory default setting is ATB0 (ITU-T tones).
This B command is not available on the MT2834MRK.
$D DTR Dialing
An alternate way to cause the MT2834MR to automatically dial is “DTR Dialing”. The Data
Terminal Ready (DTR) signal comes into the modem from the attached terminal or computer,
on pin 20 of the RS232 interface. With DTR dialing, the modem automatically dials a stored
number as soon as it receives a high DTR signal. The DTR dialing method is popular when
using the MT2834MR in synchronous applications.
To enable DTR Dialing, type AT$D1 and hit ENTER. The modem will dial the phone number
you have stored at N0 when it receives a high DTR signal (see Section 3.7.3). DTR must
remain high for the duration of the call (until disconnect). To disable DTR dialing, type AT$D0
(or AT$D) and hit ENTER.
When you use DTR Dialing, be sure that 12-Position DIP-Switch #1 is in the UP position, so
that DTR is not forced on. (Refer to Chapter 7.)
#F Fallback Modes When On-Line
If the line conditions deteriorate, the MT2834MR automatically drops its transmission speed
(fallback). The #F command controls the different ways that the MT2834MR falls back.
During operation, if the error rate becomes too great, the modem performs a rate negotiation.
If after the rate negotiation the error rate is still too high for 28,800 bps operation, the modem
will fall back to 26,400 bps.
The modem continually monitors the connection and adjusts itself, automatically and
incrementally, to the optimal line speed.
AT#F0 (or AT#F) will cause no fallback when on-line. AT#F1 will cause the MT2834MR to fall
back (based on the error rate or if three retrains have occurred within a two minute period)
from 28,800 to 26,400 to 24,000 to 21,600 to 19,200 to 16,800 to 14,400 to 12,000 to 9600 to
4800 to 2400 bps. AT#F2 enables incremental fallback from 28,800 bps to 2400 bps, but
also enables fall forward (from 2400 bps to 28,800 bps incrementally) if the phone line
improves. AT#F2 is the factory default setting.
&G Guard Tones
You can use the &G command to control the presence or absence of guard tones from the
transmitter when in Answer mode, at either 1200 or 2400 bps. Guard tones are used in
Europe and other areas, in order for the modem to function in the telephone systems. Guard
tones are not used in the United States.
AT&G0 turns off the guard tones, and is the factory default setting. AT&G1 turns on a 550 Hz
guard tone. AT&G2 turns on an 1800 Hz guard tone.
The &G command is not used on MT2834MRK units.