Siemens SIMATIC S7-1200 System Manual page 617

Communication connections
When cascading controllers, you must connect the master and slave so that they can share
information with each other. You must connect a slave's "Master" IN/OUT parameter to its
master's "Slave" IN/OUT parameter in the signal flow direction.
This shows a connection of PID_Temp controllers in a cascade with two sub-cascades:
"PID_Temp1" provides the setpoint. The configuration connects the outputs of "PID_Temp2",
"PID_Temp3", "PID_Temp5", "PID_Temp6", and "PID_Temp8" to the process:
Figure 10-8
Replacement setpoint
The PID_Temp instruction provides a second setpoint input at the "ReplacementSetpoint"
parameter that you can activate by setting the parameter "ReplacementSetpointOn" = TRUE.
You can use "ReplacementSetpoint" as your setpoint input during commissioning or tuning of
a slave controller without having to disconnect the output-to-setpoint connection between
master and slave. This connection is necessary for normal operation of the cascade.
In this way, you do not have to change your program and download it if you want to
temporarily separate a slave from its master. You only have to activate the
"ReplacementSetpoint" and deactivate it again when you finish.The setpoint value is
effective for the PID algorithm when you can see the value at the "CurrentSetpoint"
parameter.
S7-1200 Programmable controller
System Manual, V4.2, 09/2016, A5E02486680-AK
PID_Temp_Cascading_communication_connection
Technology instructions
10.2 PID control
617