Messaging between PLC 5s on Dh+

OkiePC said:

Since the Target of your message is DH+ address 20 you need to put that [20] into the "Local DH+ Node (Octal)" in the lower section labelled "Target Device"

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Have you done this?

All PLC-5/40 variants are "New Platform" PLC-5 controllers and you can use either a block of Integer (N) registers or a Message Control (MG) data element as the Control Block for the MSG instruction.

It sounds to me like you are adding new data messaging functionality to the system, so it's understandable that you need to sort out the control words and the data that's being sent from one controller to another.

Schipsys = Node 20 PLC-5/40B Sender of message
Baghouse = Node 1 PLC-5/40E Receiver of message

The built-in Help in RSLogix 5 and the PLC-5 Instruction Set Reference are both good sources of information.

It looks like you have the first part sorted out: the Control Block cannot overlap with any other data in the controller. You've changed to using an MG control block data type.

The intended data payload is just one 16-bit Word, N7:30, from the Schipsys controller. The intended destination is N7:59 in the Baghouse controller.

The MSG instruction can do both Read and Write commands. It appears that you have it set up as a Read, so the Schipsys controller is requesting the value in N7:59 from the Baghouse and placing it into the N7:30 register.

If you intend to have it work the other way around (and I think you do), you need to just change from PLC-5 Typed Read to PLC-5 Typed Write.

You never will see the N7:59 word designated as "used" in the Baghouse controller; even though it's the target of a MSG instruction, that instruciton isn't in the Baghouse program so the Baghouse controller doesn't know anything about it.

The next step is to choose which conditions cause the MSG to trigger. I like to use a repeating timer to execute ever X milliseconds, with the /EN bit used to prevent the timer from re-triggering while the message is still in process.