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7.6.1 Using LEDs to Help Diagnose Communications Problems
The communications module's Txd and Rxd LEDs can be useful indicators to help isolate system communications
problems. The LEDs are directly activated by the transmit and receive signals and provide an immediate indication
of line activity. If the Rxd LED is not illuminated, then no receive signal activity is being detected at the
communications module Terminal Block connector.
If the Txd LED is not illuminated but the Rxd LED is illuminated, then the communications module is not
responding to communication attempts. This may occur for a variety of reasons, including: 1) the communications
module and/or MJ-4 Control Panel has not been configured properly, and 2) the unit is not being addressed.
If the Comm LED is not illuminated, then the communications module is not being addressed.
If the Rxd LED is illuminated but the Comm LED is not illuminated, this indicates that the module is receiving the
transmission but does not detect its address in the message. Recheck the communications address, because it may
not be set properly.
Verify that the MJ-4 communications configuration items have been set to match the system settings. (See section
7.5, Communications Module Configuration.)
7.6.2 Using MJXplorer to Troubleshoot Communications Problems
The MJXplorer software is a menu-driven application program that allows interfacing to the MJ-4 Communications
Module. Up to three MJ-4 units may be connected at a time. When connecting the Fiber Optic interface to
MJXplorer, the auto repeat function must match the setting in the Configure Configure MJXplorer menu. See
section 4.3.1 for setting the Fiber Optic interface jumpers.
A Fiber Optic to RS-232 driver/receiver is required in order to perform these tests on the fiber optic interface. The
driver/receiver is an optical to electrical signal converter with an ST connector interface and an RS-232 interface.
Connect the optical side to the fiber optic interface via ST fiber optic patch cords. Connect the RS-232 interface to
the personal computer, Figure 7-9.
Use MJXplorer to help pinpoint communications problems in a system. MJXplorer permits testing of the
MJ-4 communications functions independent of other system components.
Once the physical connections are complete, from the MJ-4 front panel select the "2200NOA" protocol for
connecting to only one panel or select "2200" protocol and set comm addresses for connections to multiple panels.
In addition, match the Comm Parity and Comm Baud with the MJXplorer settings. Use MJXplorer to verify that
data can be retrieved from as well as written to the MJ-4 Control Panel.
Personal Computer
Running MJXplorer
Personal Computer
Running MJXplorer
20
RS-232
DB9
2
3
4
5
6
7
8
RS-232
DB9
2
3
4
5
6
7
8
Figure 7-9 MJXplorer Troubleshooting Connections
MJ-4 Fiber Optic Interface
RS-232
DB9
2
RS-232 DB9
oTx
3
to
7
oRx
Fiber Optic
oTx / oRx
Power Supply
MJ-4 RS-232/485 Interface
Txd Rxd RTN
In
Out
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Table of Contents
Troubleshooting
