DH+ MSG Error

I have 2 SLC 5/04's and a PC on a DH+ Network.

I am getting a 38Hex error code in my MSG Write block. The MSG is writing from one SLC to the other.


I have to reload both PLC programs to recover. Simetimes I can reset power to recover.

Any thoughts on what causes this problem?

Tim

38H..."Message disabled pending link response"

hmmm, bad cable? just a guess or the responding PLC is not sending the MSG, do you need a input to enable the MSG?

How do you handle the error bit from the msg?

The error bit is detected and starts a timer that in turn resends the message, continuously.

I have validated that the information has not been received.

38H, according to the manual, states "message disabled pending link response".

My interpertation is that the PLC that is being wriien to is not acknowledging.

The network cable looks fine and when I connect to the network I see all of the nodes.

I have 4 of these machine (separate networks) and I have the same problem on 2 machines.

The only way to get them running again is to reload the programs...Sometimes I can reset power to the processors and the process will resume.

If the message has been disabled (per the definition of 38H) is there a way to reset the msg without reloading or resetting the power?

That is certainly interesting. I have never seen a DH+ problem that required reloading software. You may be able to restart communication by manipulating the message control bits in ladder logic. Make sure the message rung is not enabled and then unlatch the error bit, clear the error value, etc. I have had to do similar things with C-Net message errors in a PLC5.

You may also want to monitor the DH+ status words on all four machines to compare the health of the networks. See if you are getting a bunch of retries or timeouts on the two that are troublesome. The channel must have a diagnostic file assigned before you can monitor those registers.

The cabling may look perfect and still be bruised or picking up electrical interference. Double check terminating resistors, node numbers (including the PC KT card) etc...
Also, be sure you are not over filling the message queue in the SLC. The true nitty gritty details of how DH+ works are hard to find, but there are papers out there on ab.com. There are big differences between PLC5 and SLC504. It is possible to overload the message queue. Make sure you interlock messages so that you don't trigger too many of them at once. Also, having a programing terminal connected via DH+ will hog bandwidth too and could exacerbate the problem.

PLC1 writes a message to PLC2 which writes a message to the PC....this process happens about every 10 seconds....the message is very short...

wa5yom said:

PLC1 writes a message to PLC2 which writes a message to the PC....this process happens about every 10 seconds....the message is very short...

Click to expand...

Are you saying you have a PLC with a message instruction trying to write to your PC. What software are you running on your PC?

message

This writes the msg as fast as it can, resetting errors automatically. I would lose the timer.

PLC2 write a message to the PC which is using Factory link, however the Message that is having problems is the MSG from PLC1 to PLC2.

I have not used FactoryLink but have you tried to disable it, and just have PLC1 write to PLC2? it may have something to do with the way or time, that factoryLink is handling the MSG

After the successful transmission of the MSG from PLC1 to PLC2...PLC2 then transmits the message to the Factory Link.

The problem is very intermittent.