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Chapter 5 - Command Mode
Force Answer Mode A
You can force the modem into Answer mode with the modem’s A command.
Entering ATA when in Command mode immediately brings your modem off-hook, out of Command
mode and into On-Line Answer mode, and causes it to transmit its carrier signal over the phone line.
If no responding carrier tone is received by your modem within forty-five seconds (or some other time
as determined by S-Register S7), your modem stops transmitting its tone, hangs up, and goes back
into Command mode.
Exiting Command Mode, Going Back On-Line O
You can bring the modem out of Command mode and back into On-Line mode by entering ATO
(where O is the letter O, not the number 0). In this case, the O command reverses what was done by
entering the Escape Code. The O command will bring the modem into the same On-Line mode
(Originate or Answer) that it was in prior to going into Command mode.
5.4.13 Line Probe Commands (2834 Series only)
Before V.34 negotiation takes place, remote and local modems transfer their functional capabilities
using modulated calling and answering tones; indicating the common capabilities of the modem at
each end.
Once this is done, a probing signal is passed between the modems to identify impairments in the
telephone channel (e.g., Receive Signal Strength vs. Frequency, Noise vs. Frequency and Signal to
Noise Ratio vs. Frequency). After receiving the results of the probing signal, the modem receivers
and transmitters begin with the lowest speed and move up until reaching the highest speed at which
they can exchange data. All this occurs in about five seconds.
There are a number of Line Probe Commands. These commands are configurable and can be stored
to RAM (via AT&W0).
These commands are listed below.
Enable/Disable Reading of Line Probe Information Commands:
%DP0 = Do not read Line Probe information from DSP during handshake (Default).
%DP1 = Read Line Probe information from DSP during handshake.
Format of Line Probe (Graph or Table) Commands:
%DF0 = Data is displayed in Graph format. Y axis is shown in dBms (Default).
%DF1 = Data is displayed in Table format. Numeric values are displayed for 150Hz to
3750Hz in 75HZ increments.
Immediate Action Line Probe Commands:
To activate these commands first type +++AT<CR>(on-line escape command while maintaining
command mode), then type the Command prefixed by an AT.
&RP = This command initiates a retrain that makes the processor read Line Probe
information. Valid only when on-line in V.34 mode.
L9 = Displays Signal Strength information.
L10 = Displays Signal to Noise Ratio information (SNR).
L11 = Displays noise information.