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ModbusS Interface - How Timestamp is assigned to PI Tag?

Question asked by Haque on Mar 7, 2017
Latest reply on Mar 13, 2017 by cramsey

Hi Guys,


Can you please clarify how ModbusS interface assigns timestamp to PI tag. I read in the manual that "The default state is that tag timestamps are set when a response is received". I have couple of queries, appreciate to get clarification on them.


  1. What if the response is not received to the interface and the next request is initiated?
  2. What happens if interface does not get a full data set in response to a request? Does it make a second request?
  3. Does interface writes the values that it has received from the partial data set?
  4. How will the timestamp assignment change if Timestamp is "set on request"? If request was initiated at 13:00:20 and if the complete response is received at 13:00:22, I understand that PI event will be written at 13:00:20, but if complete response was not received - this will not be recorded and a next request will be initiated as per the scan class - Is my understanding correct here?
  5. In some case, we see nterface writes 2 different data at same timestamp. What could be the reason for this? The configuration for timestamp is default on the interface and the source is configured as slave.