OPC transfers

Data change and limit value triggers for analog values

You use data change and limit value triggers if you want to transfer a single analog value. The trigger item and transfer item are identical. The transfer starts immediately after the trigger condition is met. If the OPC transfer object contains other items to be transferred, it is therefore possible that values may be transferred that do not belong together in terms of content.

Bit and message triggers for OPC telegrams

You use bit and message triggers for OPC telegrams if you want to read out several items that belong together. The OPC Router waits for another read cycle before reading the items in the OPC transfer object to ensure that the PLC was able to write all values. On the PLC side, the trigger should still be written at the end.

Recording message trigger values

Record the value of the message trigger. This allows you to track whether data records were not transferred or were transferred twice. On the PLC side, the data point for the message trigger should be increased by the value 1 when new data is received.

Always use bit triggers with response bits

Always use bit triggers with response bits. If the data point in the PLC changes twice within a read cycle, the OPC Router will not notice this. The PLC must respond accordingly to the router's lack of response. Standard practice: A bit may only be written to by one side, i.e., the PLC resets the trigger data point after receiving the response. The OPC Router resets the response data point itself after a configurable period of time.