Siemens SIMATIC ST-1500 Function Manual page 33

The basics of counting, measurement and position detection
2.2 Basics of counting, measuring and position input (TM Count, TM PosInput, Compact CPU)
Hardware interrupt
You can configure a hardware interrupt for the Capture function. Individual hardware
interrupts may be lost if the hardware interrupt rate is higher than the system
acknowledgement rate. You can signal a lost hardware interrupt with a diagnostic interrupt.
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Counting, measurement and position detection
Function Manual, 12/2017, A5E32009889-AG