Siemens SIMATIC S7-300 FM 350-1 Manual page 121

Setting the Counter with an External Signal
The L_PREPAR input parameter prepares a new load value. You can select two different
external signals with which you can set a counter to the load value:
● Only DI Set
● DI Set and zero mark of the encoder
You use the zero mark of the encoder if you want to synchronize the counter to a specific
counter status at a specific point in your process. Hence you achieve greater precision in the
count process.
The counter is set independently of the Count mode.
After the counter has been set with an external signal, bit STS_SYNC in the DB is set. The
STS_SYNC bit is cleared by the RES_SYNC bit.
Note
The synchronization of a counter with the zero mark only makes sense if the gate is open.
If you have only enabled one count direction when setting a counter with an external signal,
you must note that when the gate is closed the current count direction is saved (frozen).
Hence it is possible for the counter to be synchronized in the opposite direction to the
enabled count direction.
FM 350-1 Counter module
Manual, 05/2011, A5E03648639-01
Operating Modes, parameters and commands
7.3 Count modes
121