Experimental Physics and
Industrial Control System

"Allison, Stephanie" <[email protected]> · Wed, 25 Aug 2004 09:06:33 -0700

Hello,

Kay wrote:

> When you write "1" to the record, you should see that the
> device support deposits "1" in the tag table and after up to 1 second later,
> the driver wakes up and writes "1" to the PLC.
> Then, every second, the driver wakes up again and _reads_(!)
> from the PLC. This is meant to support the idea that Bob describes,
> where your PLC might have more than just the IOC messing with its tags.
> _If_ the driver now finds the tag on the PLC to differ from what it thinks
> it should be, so in case the driver finds the tag to be 0 on the PLC,
> it will process your record and switch it back to 0.

Just a side-note about EtherIP output records that we've seen here at SPEAR: 

Whenever the PLC is reflashed (rarely), we get errors reported by the EtherIP driver.   Also during the reflash process, corrupted (or initialized?) data from the PLC is sent to the IOC and the IOC processes it.  This results in alarm messages for the input records BUT it also results in update to the output records due to synchronization that Kay discusses above.  The output records then keep those potentially wrong states.  In particular, after a reflash, the PLC was seeing request from the IOC for valve closure when nobody asked for the valves to be closed - we tracked that problem down to the reflash and added HIGH to those bo records to automatically restore back to zero.

It is a good idea to disable all EtherIP records during a reflash (or stop the IOC).  If you have the luxury of knowing ahead of time when the reflash will happen...

Stephanie Allison

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System