DH+ MSG between two ControlLogix processors

mylespetro · Feb 13, 2020

Hey everyone,

I feel like this is an easy question, but I can't seem to find an answer for it. Currently have a PLC-5 that we're swapping out for a ControlLogix and I'm currently making some changes to a program in a different ControlLogix that reads and writes to the PLC-5 over DH+ to reflect the change, but I'm unclear exactly what protocol I should be using. The messages are currently PLC-5 Typed Read/Write, but you can't use CIP protocol over DH+, so I'm wondering what message type I use to communicate between two CLX on DH+?

Thanks in advance!

mylespetro · Feb 13, 2020

Figured it out, you need to use the explicit message path. In the PLC-5 Typed Read, it was originally set to "PLC_DHRIO" and then used the fields in the Communication Method to set the Link and Node numbers, but I had to change the path to "1, 3, 3, 10, 1, 0". This was in the manual for the DHRIO card, so it pays to RTFM.

Ken Roach · Feb 13, 2020

Exposition on the meaning of the "Port, Address" pairs in the CIP Path "1, 3, 3, 10, 1, 0"

On any ControlLogix 1756 module:

Port 1 = 1756 Backplane
Port 2 = Network Port (on DHRIO, Port A)
Port 3 = Network Port (on DHRIO, Port B)

The CIP Paths are just pairs of Port and Address values.

1, 3 From the ControlLogix CPU Port 1 (1756 Backplane) to 1756 chassis Slot 3, where the 1756-DHRIO is located.

3, 10 From the 1756-DHRIO Channel B to DH+ Station 10 (decimal), another 1756-DHRIO

1, 0 From the 1756-DHRIO Port 1 (1756 Backplane) to 1756 Chassis Slot 0 (ControlLogix CPU).

It's my understanding that this is actually transporting a PCCC message ("PLC-5 Typed Read") over CIP, because it's a full ControlLogix to ControlLogix CIP Path. You could also do a "CIP Data Table Read" or "CIP Data Table Write" because the path goes all the way from a ControlLogix to another ControlLogix.

You could probably have also kept the old execution the same, as long as the 1756-DHRIO was configured so that it knows to process DH+ messages by forwarding them to the ControlLogix in Slot 0.

mylespetro · Feb 13, 2020

Ken Roach said:
Exposition on the meaning of the "Port, Address" pairs in the CIP Path "1, 3, 3, 10, 1, 0"

On any ControlLogix 1756 module:

Port 1 = 1756 Backplane
Port 2 = Network Port (on DHRIO, Port A)
Port 3 = Network Port (on DHRIO, Port B)

The CIP Paths are just pairs of Port and Address values.

1, 3 From the ControlLogix CPU Port 1 (1756 Backplane) to 1756 chassis Slot 3, where the 1756-DHRIO is located.

3, 10 From the 1756-DHRIO Channel B to DH+ Station 10 (decimal), another 1756-DHRIO

1, 0 From the 1756-DHRIO Port 1 (1756 Backplane) to 1756 Chassis Slot 0 (ControlLogix CPU).

It's my understanding that this is actually transporting a PCCC message ("PLC-5 Typed Read") over CIP, because it's a full ControlLogix to ControlLogix CIP Path. You could also do a "CIP Data Table Read" or "CIP Data Table Write" because the path goes all the way from a ControlLogix to another ControlLogix.

You could probably have also kept the old execution the same, as long as the 1756-DHRIO was configured so that it knows to process DH+ messages by forwarding them to the ControlLogix in Slot 0.

Yes, I just posted about the path format yesterday in another thread. I've actually done CLX to CLX over DH+ (and posted about it here) before, but I guess I just never realized that the explicit path was actually required. Thanks for the info Ken, really appreciate it!

DH+ MSG between two ControlLogix processors

mylespetro

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Ken Roach

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