Siemens simatic c7-621 Hardware Installation Manual page 43

Run-Time Meter The C7 CPU is equipped with a run-time meter.
This allows you to count the operating hours of the C7 CPU or a resource it
controls.
You program the run-time meter in the user program using the SFCs 2
"SET_RTM", 3 "CTRL_RTM" and 4 "READ_RTM" (see
reference manual /235/).
C7-621 / C7-621 AS-i Control Systems
C79000-G7076-C621-01
Installing and Preparing the C7
2-25