SLC 5/05 ethernet message

Hi
I need to execute two message 'reads' from two other pieces of equipment.
I'd like to set up a sequence so one message can complete, and the message return before initiating the next message. The /DN bit seems to come on after transmitting the message i.e. not when the required data is returned.
Is there a way of doing this or do I just have to be rough and use timers.

thanks
pp

Huh... I think the MSG Read works the same way you expect, that the .DN bit comes on immediately when the data block is returned to the requesting SLC.

The timing chart for the MSG instruction in Chapter 12 of the Instruction Set Reference manual shows that the .DN bit comes on and the received data is placed in the data table simultaneously:

If the reply contains “I have successfully performed your read request, and here is your data,” the data is written to the data table, the DN bit is set and the ST bit is cleared. The MSG instruction function is complete. If the MSG rung is false, the EN bit is cleared the next time the MSG instruction is scanned.

Click to expand...

Can you share the logic that you used to send these messages ?

It's possible that paragraph is unclear and the .DN bit comes on and the incoming data is placed in the data table at the end of scan.

I recently did an experiment with rapidly-sequenced messages in ControlLogix and I found that when I waited one scan between the .DN bit and triggering the next message that I had more success sending immediately sequential messages.

Ken
Thanks for the response.
The code I'm going to try is as follows. I need to add some error recovery, but I intend that one MSG completing will trigger the next MSG to start.
thanks again - pp