Connect 2 PLC to single RIO Rack

Hi, I have a PLC5 and a PLC 5000 and a RIO rack that is currently connected to the PLC5 with 1771 cards over DH+. The 5000 has a DHRIO card that is also on the same path as the PLC5 and the RIO. Would it be possible to read IO from the RIO rack directly to the 5000 PLC while the RIO rack is still being used by the PLC5? I am looking to move the rack completely over to the 5000 but want to do it while operations still are underway so I can work out bugs and comm issues. I just wanted to know if it was possible.

The RIO rack is originally with the PLC5 system so is PLC5 1771 cards. The rest of the PLC5 racks are no longer in use and I want to put the remaining rack on the 5000 to reuse the PLC5 elsewhere. I know it is possible to use the rio over DH from the 5000 I would like to have both reading from the IO to test code simultaniously.

Not quite the way you have envisioned it though...
You will have to connect one of the channels of the 1756-DHRIO (configured as a DH+ node) to the PLC5 DH+ network and then MSG Read/Write the PLC5 data into/out of the RSL5K system.
One thing to remember though, the 1756-DHRIO will not have to be included within the RSL5K project; the DH+ bridge will have to be used exclusively as a gateway.

I believe that the A-B remote I/O is a master/slave system so it would not be possible. Two masters on the same connection will cause both to fail.

First, let's make sure we're talking about the same thing.

Data Highway Plus (DH+) and Allen-Bradley Universal Remote I/O (RIO) use the exact same wire and are frequently software-selectable on the same device. But they are different protocols and cannot be intermixed.

Mendonsy is correct; RIO is a Scanner/Adapter system and you can't have two Scanners.

dmargineau's suggestion is the simplest way to do this. If the DH+ network isn't very busy, then a frequently-triggered MSG instruction to read the whole PLC-5 Input Data Table might be fine for your application.

For migrations like this where I'm trying to work out the conversion logic and timing before the actual switchover, the product I like to use is the QTS AN-X module.

This is available in several different formats; what you want is the AN-X-ABRIO. It can be a RIO Scanner, or a RIO Adapter, or it can listen to existing RIO traffic in "Listen" or "Ghost" mode.

The AN-X-ABRIO functionality is also packaged into a 1756 series module and sold and supported by Allen-Bradley as the 1756-RIO module.

I've done project with this (and you will find other mentions of it on the Forum) in which we did all of the translation and debugging ahead of the switchover and was able to do a pretty complex system migration with a short downtime window. It costs money for hardware and engineering effort up front, but saves gigantic amounts of system downtime.

Ok, I will be doing the conversion at once over a weekend then. Right now I will be reading the input table every second or so as the application allows for several second response time. (Fan sequencing, and periodic force records)

Since everything is on DH+ I keep the 1756-DHRIO channel set to dh+ and when I switch everything to the 5000 I should set it to RIO and configure the rack from there?