Best Practice MSG bits ControlLogix -> PLC5 Only on change

Hello,

Today I am trying to figure out the best way to write from controllogix to a plc5 only on change.

The situation:
- Migrated a Winview Terminal to ViewSE.
- PLC5 is still in the field and staying there
- Have already mapped all the read registers through my DHRIO card to a set of registers in the L75 processor. The graphics are tagged the set of registers in the L75 that are constantly being updated based on MSG instructions reading the PLC5 registers
- Now I have to setup the writes. The issue is I cannot just constantly be writing to the registers because there is logic internal to the PLC5 that unlatches bits.

Anyone have an idea and can point me in that direction?

Ideas:
- Have a MSG instruction for each bit being passed (~100 different bits) and Enable the MSG based on state change of the register in the L75.
- Figure out some way of marrying the read for a bit and the write for a bit where write bits update off read unless changed by graphic.
- call tech support

Thanks,

Create an OPC topic in RSLinx Classic pointing to the PLC-5 via the DHRIO card.

Then write directly from SE to the PLC-5 bits, just like before the migration. Have SE set the Bit, PLC-5 resets.
You could have done the same with the reads too, bypass the L75 completely.

Tags look something like this:
{::[OLD_PLC5]B:24/1}


(With SE you can use RsLinx Classic Lite for OPC topics, without having to pay for the OEM license).

Maybe have a separate MSG instruction for each Word of Bits being passed and trigger it only when a word containing the transfer bits is not equal to another word that holds the value of that particular bit transfer word from the prior sweep.

After examining whether each "bit transfer word" is Not Equal to the "value last sweep" word, then unconditionally move the "bit transfer word" to the "value last sweep" word on the very next rung. Only trigger the MSG when the two words are not equal.

That's what I do when I want to write a MSG only on exception. I am assuming that this is your goal?

Ken Moore said:

Create an OPC topic in RSLinx Classic pointing to the PLC-5 via the DHRIO card.

Then write directly from SE to the PLC-5 bits, just like before the migration. Have SE set the Bit, PLC-5 resets.
You could have done the same with the reads too, bypass the L75 completely.

Tags look something like this:
{::[OLD_PLC5]B:24/1}


(With SE you can use RsLinx Classic Lite for OPC topics, without having to pay for the OEM license).

Click to expand...

Thanks so much! I had given up on getting the topic to go through this way after talking with tech support and others a few months ago. The thing that was missing was the routing table config for the DHRIO card. After I filled out the link IDs it was good!