Siemens SIMATIC S7-1200 Function Manual page 345

Block diagram of PIDT1 with anti-windup
Call
PID_3Step is called in a constant time interval of the cycle time of the calling OB (preferably
in a cyclic interrupt OB).
Download to device
The actual values of retentive tags are only updated when you download PID_3Step
completely.
Downloading technology objects to device (Page 44)
Startup
At the startup of the CPU, PID_3Step starts in the operating mode that was last active. To
leave PID_3Step in "Inactive" mode, set RunModeByStartup = FALSE.
PID control
Function Manual, 03/2017, A5E35300227-AC
Instructions
9.2 PID_3Step
345