Dh 485 msg

I have a micrologic 1000 that has a msg read and msg write to an slc that is supposed to be node 1. After troubleshooting intermittent comm issues I discovered The SLC was actually node 7 on its ch1 dh485. How on earth did this work ?

Can you ZIP the program and attach it?

Is channel 1 being used for this communication? Most SLC's have 2 channels. Are you sure the other channel is not being used for this?

Post both programs if you can. Zip them first. Someone can take a look. (ditto geniusintraining)

zipped prog

12065 la contains msg to 1 slc at node 1 and another slc at node 5

They both work but the node 1 has intermittent issues . the 2 slcs are actually node 7 and node 5

here is the print

I enclosed the print showing the setup

Steve, welcome to the PLC Talk forum community. You've brought diagrams and program files to your first thread, which is awesome.

My first take is that the program file you have that shows the SLC-5/03 as DH485 Node 7 must be incorrect, and that the controller is actually at Node 1.

That would explain why the MSG in the MicroLogix works at all, and it would be consistent with the network diagram.

The way to figure it out would be to get online with the DH485 network, through the 1747-KE or a 1747-UIC, and browse the network nodes.

I have a guess (I have to run to a meeting and won't be able to explain in detail) that the T4:32 and T:33 timers in the MicroLogix LAD8 file, and the way they are used to trigger and interlock the MSG instructions, are why the Node 1 message seldom works.

The way I read it, unless the MSG on Rung 16 completes in under 20 milliseconds, its /EN bit will prevent the timer from triggering the MSG on Rung 14.

There are other ways to write timed MSG triggers... more on that later.

I will bow out and let Ken answer... one thing I would like to add is I dont see 5d I see 1 writes/reads to 4 and 7

I worked on a DH+ system once that they had some writes and the nodes on the other end you had no idea where it was coming from but at least it looks like you have good documentation, is it possible that someone changed 5 to 7?

The only thing that makes sense is that the SLC-5/03 program that was Zipped and attached, which is clearly set as DH485 Node 7, is actually installed as DH485 Node 1.

The only reference I see to Node 7 is in the zipped SLC-5/03 program. It's not addressed by any of the MSG instructions I saw in the MicroLogix program.

An examination of the actual network, and/or the other SLC-5/04 program, and/or the PanelView Plus configuration, might help settle that. The most helpful thing would be a browse of the actual network.

There is no realistic possibility that the MSG instructions from the MicroLogix (Node 4) to DH485 Node 1 are working, ever, if that SLC-5/03 is actually configured and running as Node 7.

By "no realistic possibility", I mean that in a billion years the correct coincidence of checksum and data corruption will eventually occur. But not often enough to be "intermittent" in the scale of human lifetimes.

Thanks

Thanks much for your help. I have found more answers in PLCTalk than anywhere else.