Siemens SIMATIC ST-1500 Function Manual page 192

Complete acknowledgment principle
Saving bits are acknowledged according to the complete acknowledgment principle.
The figure below shows an example of the sequence of the complete acknowledgment
principle in the event of an overflow:
①
②
③
④
⑤
Counting, measurement and position detection
Function Manual, 12/2017, A5E32009889-AG
The EVENT_OFLW feedback bit is set as a saving event upon overflow.
You set the RES_EVENT control bit to trigger EVENT_OFLW reset.
The RES_EVENT_ACK feedback bit is set when reset of EVENT_OFLW is detected.
You then rest the control bit RES_EVENT .
The RES_EVENT_ACK feedback bit is reset.
Using the module
5.1 Using the technology module
191