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Chapter 3 - AT Commands
3.15 Line Probe Commands
Before V.34 negotiation, the local and remote modems use modulated calling and answering tones to
exchange capability information . If V.34 mode communication is successful, probing signals are exchanged
to identify impairments in the telephone channel. Using the results of these line probes, communication
parameters are set, including carrier frequencies and data rates used for transmission. The following
commands apply to modems only in V.34 mode.
%DP
n Read Line Probe Data
n
= 0 or 1
Default:
%DP0
The modem does not normally store data acquired during line probe. To examine the line
probe data using the
L9
,
L10
, or
L11
commands, set the
%DP1
command to read and store
line probe data.
%DP0
disables reading of line probe information during the handshake.
%DP1
enables reading of line probe information during the handshake.
%DF
n Format Line Probe Data
n
= 0 or 1
Default:
%DF0
Use this command to selects line probe data displayed as a graph with the Y axis showing
signal strength in dBm, or as a table with dBm values shown numerically. The graph format
shows data in 150 Hz increments from 150 Hz to 3750 Hz. The table format shows data in
75 Hz increments from 150 Hz to 3750 Hz.
%DF0
displays line probe data in graph format.
%DF1
displays line probe data in table format.
&RP
Immediate Line Probe
Default: none
This command initiates a retrain that makes the processor read line probe information for
display using the
L9
,
L10
, and
L11
commands. Before issuing this command, escape to
command mode while remaining online. To combine both actions, use the following
command string:
+++AT&RP<CR>
.
The modem will not read and store the line probe information from this retrain unless a
%DP1
command is first issued.
L
n Display Line Probe Data
n
= 9–11
Default: none
These immediate action commands cause the modem to display line probe information
when it is in V.34 mode. The line probe information must first be read and stored by the
modem (see “Read Line Probe Data”). Data format is controlled by the Format Line Probe
Data command,
%DF
.
The display commands are valid only in online mode. To use them online, you must first
escape to command mode with
+++AT<CR>
. To return online, enter
ATO
.
ATL9
displays signal strength information.
ATL10
displays the signal to noise ratio (SNR).
ATL11
displays noise information.