Allen-Bradley Logix5000 Reference Manual page 668

Appendix B Function Block Attributes
668
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.
In this example, a rung of ladder logic in another routine is used to one-shot latch
a ProgAutoReq to a PIDE instruction when a push button is pushed. Because the
PIDE instruction automatically clears the Program mode requests, you don't have
to write any ladder logic to clear the ProgAutoReq after the routine executes, and
the PIDE instruction will receive only one request to go to Auto every time the
push button is pressed.
When the TIC101AutoReq push button is pressed, one-shot latch ProgAutoReq for the PIDE instruction TIC101.
TIC101 has been configured with the ProgValueReset input set, so when the PIDE instruction executes, it
automatically clears ProgAutoReq.
Rockwell Automation Publication 1756-RM003N-EN-P - October 2011