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X7 causes the modem to wait for a dial tone before dialing. If it doesn't detect a dial tone within the
time set by S6, the modem sends only the basic result code to the terminal (ERROR, NO CARRIER,
or CONNECT, for example). In this mode, the modem does not respond to busy signals.
&Qn
Asynchronous Communications Mode
n = 0, 5, or 6
Default: &Q5
Allows you to select the type of asynchronous communications mode for your modem.
Note: These commands are the same as several of the \Nn commands, described later in this
chapter.
&Q0 selects asynchronous mode with data buffering. This is the same as \N0, nonerror correction
mode with data buffering.
&Q5 selects error control with data buffering. This is the same as \N3, V.42/MNP auto-reliable mode.
&Q6 selects asynchronous mode with data buffering. This is the same as \N0, non-error correction
mode with data buffering.
Online Connection Commands
The following commands control the conditions of the online connection.
Bn
Answer Tone
n = 0, 1, 2, 3, 15, or 16
Default: B1 and B16
Selects the frequency the modem uses for its answer tone. (The answer tone is the tone transmitted
by the receiving modem to the calling modem, thus initiating the handshake between the two
modems.) At higher speeds (2400 bps and above) there is no conflict because all protocols use the
Bell frequency of 2225 Hz. Lower speeds require different frequencies.
B0 selects ITU-T V.22 mode when the modem is at 1200 bps.
B1 selects Bell 212A when the modem is at 1200 bps. This is a default.
B15 selects V.21 when the modem is at 300 bps.
B16 selects Bell 103J when the modem is at 300 bps. This is a default.
Cn
Dummy Command
-Cn
Data Calling Tone
n = 0 or 1
Default: -C0
The data calling tone is a tone of a certain frequency and cadence, as specified in the V.25
standards, which identifies whether it is remote data, fax, or voice. The frequency is 1300 Hz, with a
cadence of .5 s on and 2 s off.
-C0 disables the V.25 data calling tone.
-C1 enables the V.25 data calling tone.
F
Dummy command
&Gn
Guard Tones
n = 0, 1, or 2
Default: &G0 (models outside U.K.) or &G2 (U.K. models only)
Controls 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 to allow the modem to function in
the telephone systems. Guard tones are not used in the United States. U.K. models are locked at
&G2 (1800 Hz guard tone).
&G0 disables ITU-T guard tones.
&G1 enables ITU-T 550 Hz guard tone.
&G2 enables ITU-T 1800 Hz guard tone.
RF300E/RF310E
Appendix F - Modem AT Commands
171
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