Siemens SIMATIC S7-1200 Function Manual page 463

Automatic synchronization
It is possible to automatically synchronize the pulse output with the instruction that updates
the input variable INV (e.g. CONT_C). This ensures that a change in the input variable is
output as quickly as possible as a pulse.
The pulse shaper evaluates the input value INV at intervals corresponding to the period
duration PER_TM and converts the value into a pulse signal of corresponding length.
Since, however, INV is usually calculated in a slower cyclic interrupt class, the pulse shaper
should start the conversion of the discrete value into a pulse signal as soon as possible after
the updating of INV.
To allow this, the block can synchronize the start of the period using the following procedure:
If INV changes and if the block call is not in the first or last two call cycles of a period, a
synchronization is performed. The pulse duration is recalculated and in the next cycle is
output with a new period.
The automatic synchronization is switched off, if SYN_ON = FALSE.
Note
The start of a new period and subsequent synchronization usually leads to a certain
imprecision when the old value of INV (i.e. of LMN) is mapped to the pulse signal.
PID control
Function Manual, 03/2017, A5E35300227-AC
Instructions
9.4 PID basic functions
463