Verify The Communication Links; Verify The Routing Tables; If All Else Fails - Allen-Bradley AB QUALITY ControlLogix 1756 Series User Manual

11-2 Troubleshoot the System
Verify the Communication
Links

Verify the Routing Tables

If All Else Fails. . .

Publication 1756-6.5.13 - September 1999
1. Perform an RSWho to determine which devices are on line.
2. Examine the diagnostic counters. If you notice CRC errors, they might
indicate noise or intermittent connection problems.
3. Verify that each link is properly terminated.
Compare your routing table with those shown in the example applications.
Do they look similar? If they do not, try the following:
1. Verify the paths in the routing tables, in both forward and reverse
directions.
Do the paths go far enough to reach the destination?
Are the paths complete?
Do the paths include the link ID for the local port?
Are all of the node numbers and slot assignments correct?
2. Verify the link IDs in the source MSG instruction, in each of the
1756-DHRIO modules, and in the destination's channel configuration.
1. Verify the channel configuration.
2. Check the MSG instruction. Ensure that the parameters are correct.
Examine the status bits to verify that the instruction is actually trying to
send a message.
3. Examine the error codes in the device sending the message. Keep the
following in mind:
• "local link timeout" indicates that the PLC processor cannot find the
first bridge
• "application timeout" often indicates a problem in the return route
• "D0" indicates that the first bridge is not correctly configured or that
it has other problems in trying to reach its destination
4. Examine the diagnostic counters. Specifically, look at the "requests sent"
and "replies received" counters in the device sending the message.
Compare these with the values in the "requests received" and "replies
sent" counters in the destination device.