Diagnostics and Trouble Shooting
Dialup / Leased Line Modem
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The following are possible causes of failed connections and a possible course
of action if any of the problems are encountered.
1. Incorrect or damaged cable.
Check the green indicator lights “DTR”, “RTS”, “DSR” and “CTS”. All lights
should be on. Also check the yellow “TX” light it should flash when the
device connected to the RS232 port transmits the dial command.
If you are not getting the “DTR” and “RTS” lights but the “TX” light flashes
then you may have a damaged cable or a 3 wire RS232 cable. If the “TX”
light does not flash you may have a null-modem cable. If the “TX” light
does not flash then you will need a replacement cable.
The DLM can be configured to ignore missing “DTR” and “RTS” signals for
use with 3 wire RS232 cables.
The default settings for the DLM for Dial-Up operation are set to recognize
the DTR line. DTR is typically used to hang up modems such as the DLM.
The DLM can be set up to operate without a valid DTR signal however
when disabled the only way to force a hang up is with the escape sequence
of “+++” followed by the “ATH0” command.
When used for Leased-Lines, the configuration options contained in the
“Getting Started” section disable DTR detection.
To disable DTR detection enter: AT&D0
You may also want to disable hardware handshaking by entering: AT&K0
Hardware handshaking will not prevent the DLM from making a connection
however it will prevent data from being transferred.
2. A connected device may be causing the DLM to disconnect.
a. If using a Dial-Up connection, the device performing the dial out is not
giving the DLM time to make the connection. The connection time
includes the time the dial takes to negotiate the phone system, the time
it takes for the remote modem to answer, and the time it takes to make
the connection.
You may check for this possibility by observing the “DTR” and “TX”
lights. The “DTR” light should remain on except at the beginning of a
dial out. The “TX” light should not flash until connected. Neither light
should flash while a connection is in progress.
Set the dialing parameters in the device dialing out to 2 minutes or
longer. Two minutes is more than double the time it takes for a typical
