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BC_108811341-Visitor
1-Visitor
March 13, 2026
Question

Linked tags doesn't update after communication fault with PLC

  • March 13, 2026
  • 1 reply
  • 142 views

I use KepserverEX6.14 for linking Rockwell and siemens PLC's.

We have 207 link tags in both directions.

 

But we have troubles with 1 Siemens 1512 PLC when the communication drops (without voltage or network troubles). After the communication restores, kepserver can read the datablocks but CAN'T write to the datablock.

 

The solution is then disable-enable tags, after this everything works like it should.

 

My datatypes are boolean's and words (not defaults).

There is a scan rate of 2000ms for PLC values. And the linked tags are written when input changes.

I have tested with Auto-Demotion on and off (also with 'Discard Requests when Demoted' on/off)

 

What can i try else?

1 reply

R
rajskumar16-Pearl
16-Pearl
March 13, 2026

Hello,

 

Are you receiving any error, such as “write failed”?

 

You may try adding a Simulator channel and device in Kepware, link the same input tag to a simulated tag, and observe the behavior. If it works fine, then you may need to check using Wireshark to see what is happening.

Thanks

B
BC_108811341-VisitorAuthor
1-Visitor
March 16, 2026

Hello,

 

I get the error "unable to write to address on device xx". But the strange thing is that for example the last timestamp of the error is 1:47PM but 8h later the link tag isn't active. I must manually Stop-Start the tag.

 

There are 8 tags, 7 booleans and 1 word. The booleans are part of the same Byte in a DB. Some of the booleans are updated after the communication is restored.

 

I have now created a simulation device. But the communication will never fails because it is a virtual device?

 

Regards, bram

 

R
rajskumar16-Pearl
16-Pearl
March 16, 2026

Hi,

My suggestion was to link the Siemens tag to a simulator tag to see if it behaves the same as the existing linked tag. After the issue occurs (Siemens communication failure), check whether it can still link data successfully to the simulator tag.

 

Also, any tags that are written to (used as output tags) should have a specific data type set and should not be left as “Default.” Please make sure the output tag has a defined data type.

Thanks 

 

 

 

 

 

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