ControlLogix 1756-DHRIO Comms Issue

[BobLfoot 302]

Had a rather strange problem with a 1756-DHRIO card on one of our systems today.

First the Hardware Layout - 

PLC A - ControlLogix 13 Slot Chassis

              Slot 0 - CPU

              Slot 1 - 1756-ENET 10.5.1.10

              Slots 2 through 11

              Slot 12 - 1756-DHRIO 1 = Channel B Node 52

PLC B - ControlLogix 13 Slot Chassis converted to 7 Slot Chassis

              Slot 0 - CPU

              Slot 1 - 1756-ENET 10.5.1.20

              Slot 2 - 1756-ENET 10.3.1.20

              Slot 3 - 1756-CNB ControlNet

              Slot 4 - 1756-DHRIO 1 = Channel B Node 32

PLC C - PLC 5 at Node 20 DH+

PLC D - PLC 5 at Node 1 DH+

Second the actions prior to the malfunction

          PLC B was changed from a 13 slot to a 7 slot chassis with no change in other hardware.

Third the Issue with the system

          Using RSlinx and Browsing 10.5.1.10 to Slot 12 and Channel B I see nodes 1, 20, 32 & 52.

          Using RSlinx and Browsing 10.5.1.20 to Slot 4 and Channel B we see only node 32

Fourth - we moved the 1756-DHRIO to Slot 6 and it browsed the same.

Fifth when we changed the card back to Slot 4 and rebrowsed we saw node 1, 20, 32 & 52.

I can't explain why the card would start working after several minutes.

[pturmel 160]

Those cards contain a configurable router.  By default, it just learns what is around it.  Losing some local slots may have discombobulated it.

[BobLfoot 302]

Did not know that about the self learning router.  

[pturmel 160]

I don't think it is documented as "self-learning", but seems to behave that way.  You can override it to provide routing rules that make ethernet devices appear to be remote DH+ to PLCs on the DH+.