Rockwell Automation 198 Series C Modular DeviceNet Starter Auxiliary User Manual - Manual (Page 132)

6-2 Troubleshooting
Publication 198-UM002A-EN-P December 2001
The MDSA system constantly checks the validity of the module combination that it controls.
If the DeviceNet Module finds the correct number of modules, but the order or mix is
incorrect, it will generate an I/O error code 3, Module Different. This typically occurs after
some maintenance activity. Again, the location of the different module can be found by
reading Attribute 26 of the DeviceNet interface object (class 180). Powering down and
correcting the module order will reset the fault condition. If the new configuration is desired,
then accept the configuration and it will be stored.
Red I/O Light — Noise
If the I/O light turns on after a large coil such as a contactor has been turned on, the problem
may be that high frequency noise is finding its way into the product. This typically happens
when the same power supply is used for DeviceNet power as well as control power for the
coil. However, there are scenarios where tracing the high frequency noise is more difficult. In
both scenarios, it is recommended that a diode suppressor be installed across the terminals of
the coil. Rockwell Automation contactors with integrated diodes are recommended for ease
and simplicity.
DeviceNet Connection and Autobaud
The first area of interest is to be sure that the DeviceNet connection has been properly made.
Upon the application of power, both LEDs on the DeviceNet Module appear green followed
by red. This indicates that the DeviceNet board has powered up and is functioning. While the
unit is determining the network baud rate, the Mod/Net status LED will blink green for ¼
second, red for ¼ second, then turn off.
Once the proper baud rate is set, the Mod/Net LED will either blink green, or turn solid
green if a connection is established between it and another device. The Mod/Net LED will
turn red if the unit is attached to a network with the incorrect baud rate, or if a duplicate MAC
ID is found. Once the master node has made a connection with the module, the Mod/Net
LED will be solid green.
Low DeviceNet Voltage
There are a number of events that could cause a unit to go off-line. One possible cause would
be that the DeviceNet Bus voltage would drop below 11V. This would be indicated by both
status LEDs going to the Off state. When the bus voltage drops below this minimum level,
IMPORTANT
If there is no traffic on the network, the device will not be able to
determine a network baud rate. The Mod/Net status LED will
continue to execute the above sequence until network traffic is
detected.