You would be better served using the new data received (or ready, NDR) output to reset a timer.  If the timer reaches a predetermined time (say 1sec), you can then trigger a loss of communications alarm within your logic.

Of course, if you have to send before receiving, you can always send a sign of life request once a second - where the request's response is of no consequence, just knowing it is still responding is what you care about.

Not all modules support all / any GET_DIAG modes.

Do you receive a PLC diag buffer entry when you disconnect the comm cable?

EsiGtek

Hi,

We have a CM ptp module (137-6AA01-0BA0) and the diag. LED is solid green even the serial cable to the module is disconnected and "Active Break Detection" and  "Enable diagnostics interrupt" are both enabled, so as the diagnostic of the module in TIA shows no error!

To get more diag. data, I setup GET_DIAG in TIA V20 and then I made the data block with Struct datatype inside with the same structure in the manual, but RET_VAL returns #8081 in either mode 1 with DIS or mode 2 with DNN and does work only with mode 0 which returns #F.

Any help would be appreciated.

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Split from Get_Diag instruction: configuring "Diag" formal parameter?.