CODESYS - the IEC 61131-3 automation software

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PostPosted: Tue Oct 04, 2016 12:55 pm 

Joined: Wed Sep 21, 2016 12:51 pm
Posts: 1
I'm using Codesys OPC Server v3.5 SP9 to communicate with ABB PLC's over Codesys Gateway v2.3.
Using old version of OPC Server (v2.3), when connection went down between server and PLC, item values remain with last good value.
With new version of OPC server I don't know how to do that and all item values go zero when communication breaks down.
There are any configuration to freeze last good values? In my sistem this fact is very important.

PostPosted: Fri Nov 11, 2016 5:25 am 
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Joined: Fri Sep 02, 2011 8:02 pm
Posts: 255
You may have to implement some code that determines if the communication has stopped and latches the values itself. Maybe the OPC server implementation was changed... this discussion on what to do - hold values or set to 0 is not something that can be resolved. Depending on the application, the "best" solution changes.

I had a system that used a EthernetIP to Profibus gateway - it held the value when the communication stopped. I had no way of tripping a fieldbus error. I ultimately I had to have the host toggle a bit between every transmission. I setup two timers on the receiver - one reset the count when the bit was high, and the other reset when the bit was low. If either reached 50ms, I lost communication.

Maybe you could have the host toggle two bits (opposite of each other) - if both are 0, then you have lost communication - don't use the new values. Additionally, don't update your values unless the bits actually flipped.

Scott Cunningham
KEB America, Inc.

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