Allen-Bradley LOGIX 5000 Reference Manual page 504

Chapter 9 Function Block Attributes
control until it receives a request to change. For example, the operator could set
the OperOperReq input from a faceplate to take over control of that instruction.
The following example shows how to lock an instruction into Program control.
Operator request inputs to an instruction are always cleared by the instruction
when it executes. This allows operator interfaces to work with these instructions
by merely setting the desired mode request bit. You don't have to program the
operator interface to reset the request bits. For example, if an operator interface
sets the OperAutoReq input to a PIDE instruction, when the PIDE instruction
executes, it determines what the appropriate response should be and clears the
OperAutoReq.
Program request inputs are not normally cleared by the instruction because these
are normally wired as inputs into the instruction. If the instruction clears these
inputs, the input would just get set again by the wired input. There might be
situations where you want to use other logic to set the Program requests in such a
manner that you want the Program requests to be cleared by the instruction. In
this case, you can set the ProgValueReset input and the instruction will always
clear the Program mode request inputs when it executes.
504 Rockwell Automation Publication 1756-RM006K-EN-P - November 2018