1756 DHRIO communication timeout

Hi all, I'm stuck on this problem and I'm having a hard time finding information anywhere on it. I was hoping that some of you might be able to help me.

We have a DHRIO module that we are using to control some VFD's. We are using Channel-B as a RIO scanner to communicate. This form of communication has worked fine for years now, up until recently. What changed is that we added a lot more Point IO's and more logic to compute the information. Now all of the sudden the DHRIO faults. It faults every few days or so, sometimes back to back days, but it usually fautls in the morning.

The error code on the PLC for that module reads "(Code 16#0016) Service request error; unknown object" which I believe is a timeout issue. In the Properties for that module the internal state showed "(16#0131)unknown"

The RPI for that module was 500ms, so I took it up to 750 (max) and it still faulted. I tried replacing the module with a new one and it still faulted . I checked the connections and they look good on the VFD's.

My rack consist of the 1756-L61 controller, two ENBT/A Ethernet modules, a Slot Server Module (150ms RPI), and the DHRIO module.

On one of the Ethernet modules we now talk to 53 Digital IO modules (Rack Optimized 100ms RPI), and 55 various Analog modules (80ms RPI) through a combination of 11 differnt Flex IO, Point IO, and Ethernet modules. Plus we talk to around 5 newer VFD's (700&500 series).

I have a few questions. #1 is; we have the Digital IO modules rack optimized, yet some were reading 20 for the RPI. Does the RPI of each individual module matter when the Rack has been optimized?

#2; how does the RPI of of these Point IO modules affect the processors ability to talk with the DHRIO module that is on the backplane? Does the DHRIO have to wait its turn to talk?

#3; How does the RPI rate work? If they are all set at the same rate, do they try and communicate at the same time? Do they take turns? And how does the CPU procces them? In what order?

#4; Do the modules push information to and pull information from the CPU? Or does the CPU pull infomation from and push information to the modules?

#5; In your experience, are we overloading this CPU with too much information to process in a timely fashion?

Understanding these questions will help me a great deal; sadly, I'm finding it hard to track down this information.

Anyhelp would be much appreciated!

-Ken

I am also having a similar problem with our 1756-DHRIO (E rev 7.003).

We are using it to connect with 11 remote IO modules on channel B and less than a dozen other PLCs with DH+.

The remote IO faults every 15 minutes to 48 hours. During the time before the errors some of the connected remote IO modules (1771-ASB, 1794-ASB or 1747-ASB) will get 16#0203 timeout errors which last only a split second. After the error occurs all the ASB modules will fault together with "16#0016 Service request error: unknown object" which we haven't been able to clear without cycling power. The DHRIO module itself doesn't have any errors usually in this condition, but one time it did have a 16#0002 error which only occurred after the remote IOs had been faulted for 45 minutes.

The problem occurred more often when all the RPIs were set below the recommended 55ms (5ms per rack at 115.2 kHz Baud rate, 3ms per rack at 230.4 kHz and 8ms per rack at 57.6 kHz), but also occurred when the RPI was set above it (70ms or 80ms). It hasn't occurred yet though when RPI was set to exactly 55ms (although we have only had it like that for 12 hours so far, so we don't know if that will be a permanent fix).

The next thing that we will try if we still are having problems is changing the Baud rate to 57.6 kHz.