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SERIES II INTELLIGENT DATA/FAX MODEMS
5.4.6 Phone Line Conditioning Commands
Guard Tones &G
The &G command is used 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 for the
modem to function in the telephone systems. Guard tones are not used
in the United States. &G0 (default), turns off CCITT guard tones. &G1
turns on 550 Hz guard tones. &G2 turns on 1800 Hz guard tones.
Phone Line Monitoring Speaker M
The Series II Modem has an internal on-board speaker, which functions
like the speaker in a telephone handset, to enable you to monitor
phone line activity. The M command can be used to determine when
the speaker is operational.
Entering ATM0 disables the speaker completely, while ATM1 causes the
speaker to be on only until a carrier signal is detected. ATM2 causes the
speaker to remain on at all times. ATM3 causes the speaker to be on
during dialing and off during handshake. ATM1 is the default setting,
and the one that should be used in most applications.
Enable or Disable Recognition of Remote Digital Loop
Signal &T
The Series II Modem has several self-test features (covered in Chapter
8). The tests are activated with different U commands, such as ATU1,
and so forth. The &T command is a phone line conditioning command
that enables or disables the modem’s ability to recognize the Remote
Digital Loop (RDL) test signal.
The AT&T4 command lets the Modem respond to a RDL signal, and
places itself in digital loop. The AT&T5 command causes the modem
to ignore the RDL signal. The factory default is &T5.
Enable/Disable Trelis Coded Modulation #T
This command enables or disables the Trellis Coded Modulation of the
Series II Modem. There is usually no need to disable (turn off) Trellis