INSYS Modem 336 LL
i-modul Modem 336 LL
Diagnosis and Testing of the Path
Aug-06
9
3
Diagnosis and Testing of the Path
3.1
Line Optimization
To query the line quality and the received signal level a connection must be established
between the two modems (
CONNECT
).
Use the Escape sequence “+++” (with > 1 second pause before and after the sequence) to
switch to the online command mode.
Activate the level with the command
AT%L
. The displayed value in the scale – dBm is not
equivalent to the line level but the level within the data processor part of the modem.
The modem will be able to recognize a remote terminal up to the level value –40. The
optimum values will be around 20.
The command
AT%Q
queries the connection quality. Lower values indicate a better line
quality with a less significant error rate – for connections that have not been error-
corrected – and a higher data transfer rate for error-corrected connections.
The command
ATO
terminates the online command mode.
3.2
Error Sources
If the modems don’t establish a
CONNECT
at all, the following reasons could apply:
¾
The two remote terminals were set to different connection protocols (V.xx,
to be set with
AT+MS=<n>
).
¾
The two remote terminals are fixated on different error correction proto-
cols (None, MNP, V.42).
¾
a1/b1 and a2/b2 have not been connected crosswise during four wire op-
eration.
¾
The transmit level is too strong or too weak (check with a level gauge or ad-
just the S registry (
ATS91
) on both sides).
¾
Strong interferences occur on the line (e.g. if the line has been running par-
allel to lines with high interference voltages).
¾
The baud rate or the data format of the serial interface has been set incor-
rectly. Therefore the modem can not receive or send valid data.
3.3
Data Protocol Dependant Settings
Depending on the type of the transmitted data it may be necessary to change the basic
settings of the modem.
This concerns on the one hand the flow control (RTS/CTS, XON/XOFF, or no flow control)
and on the other hand the error correction/data compression.
The flow control is set with the command
AT&K<n>
, like for a switched line modem. Per
default the flow control is deactivated (
AT&K0
).
Error correction and data compression are activated in the factory settings.
If this leads to invalid delays for short data messages, the data compression
should be switched off with the command
AT%C0+DS44=0
first.
