Siemens SIMATIC S7-1200 Function Manual page 310

Instructions
9.2 PID_3Step
Block diagram of PIDT1 with anti-windup
Call
PID_3Step is called in the constant time scale of a cycle interrupt OB.
If you call PID_3Step as a multi-instance DB, no technology object is created. No parameter
assignment interface or commissioning interface is available. You must assign parameters
for PID_3Step directly in the multi-instance DB and commission it via a watch table.
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
When the CPU starts up, PID_3Step starts in the operating mode that is saved in the Mode
in/out parameter. To leave PID_3Step in "Inactive" mode, set RunModeByStartup = FALSE.
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Function Manual, 03/2017, A5E35300227-AC
PID control