Maintenance and diagnostics
65
Building Technologies
048_DMS_NK8237_ICC_MP4.40_A6V10316241_a_en.doc
Fire Safety & Security Products
06.2011
9.4
Correcting communication failures
9.4.1
Modbus communication problems
If a communication fault occurs on the Modbus, there may be one or more causes.
The problem may be in the NK8237 unit, or in the connections.
Check the NK8237
Check power, vital function, and diagnostic state on the respective LED, which is
located on the front panel.
Note:
If you need to modify the IP address because of a network change, you
might want to reset the device back to factory configuration by setting DIP-switch 1
or 2 to ON (see 4.1.2 at p. 13) and then connect on the known address to change
the IP address.
Check the serial connections (Modbus serial)
Diagnostic information about the serial line state can be obtained from the LEDs
placed on the front panel of NK8237.
General
problems
Check to make sure all connections are correct, tight and that the quality
of the cable is good.
Disturbances, caused by ground loops, if more than one device connects
the shield to ground. Also, check that the shield is not grounded in the
middle of the cable, e.g. because it is accidentally connected to some
grounded metal object.
Electric motors, high voltage power lines, radio transmitters, microwave
ovens or other sources of electrical noise near the line may cause com-
munication errors.
RS232
Typical problems of RS232 communication:
Make sure that line length does not exceed the maximum of 15m. Solve
problems of exceeding line length by using:
RS232 line drivers
Fibre optic converters
RS422
converters
RS485
Typical problems of RS485 communication:
In a multi-drop RS485, a device with a bad serial port can cause prob-
lems on the entire network. Try removing the devices one at the time.
Termination and/or biasing problems may occur if the cable is very long
or if there are many RS485 devices on the same cable. Check to make
sure that the line is properly terminated.
Check the network connections (Modbus TCP/IP)
LAN
Diagnostic information about the LAN state can be obtained from different lay-
ers:
Link state LED of Repeater or Ethernet adapters gives you information about
the physical connection and the speed of the Ethernet link.
1) Select Start
Programs
Accessories
Command Prompt.
2) Choose from the following commands: