I have a project where I am converting 2 AB PLC 2/30s and one PI 5/250 to 3 separate CL 1756-L55 . The existing RIO modules and racks are remaining, and I am communicating via RIO using the 1756-DHRIO module. I understand there may be some issue with series A 1771-DB basic modules , where if more than one exists on the same rack, the BTR and BTW may hang. Another competitor integrator I know of is doing a similiar project and is experiencing this particular issue.
Has anyone done the above, and experienced this issue?
Thanks
Ian Phillips

 

I have experienced this same, or perhaps a similar problem. It's a known bug with the I/O racks themselves. Certain series of earlier I/O racks will not work reliably with 1771-DB modules in remote racks IF the DB module is in the last 4 slots of a 16 slot rack.

This is actually a problem with all block trabsfer modules in earlier remote racks in my experience. I have seen the same thing happen with analog modules located in remote racks. It seems particularly common when using continuous block transfer mode.

Bob Peterson

 

Ian---

I was intrigued by your question, and spent some time looking around the KnowledgeBase (http://domino.automation.rockwell.com/applications/kb/RAKB.nsf/$$Search/?OpenForm) without finding a reference to this. The Series A DB modules had their own quirks, and the DHRIO has some as well, but as far as I know, your
application should work.

If you do have problems, this is the sort of thing that you should take to Rockwell's phone support.

Hope this helps!

Larry Lawver
Rexel / Central Florida

 

I received more clarification of the problem after talking more with the other integrator.
To recap , a Contrologix with 1756-DHRIO was used to replace obsolete AB legacy PLCs CPUs. Existing I/O utilized on RIO connected to 1756-DHRIO.

Draw your own conclusion from the following:

1) 1771-DB with a 40 line program worked continuosly

2) 1771-DB with a 100 line program timed out occasionally

3) 1771-DB with 600 line program did not work at all,

but all three modules worked without fail once the original PLC 5/250 was reinstalled.

Ian