Rockwell Automation Logix5000 Controllers Function Block Diagram Programming Manual - Manual (Page 18)

Chapter 1 Program a Function Block Diagram
Program or Operator control is determined by using these inputs:
Input Description
.ProgProgReq A program request to go to Program control.
.ProgOperReq A program request to go to Operator control.
.OperProgReq An operator request to go to Program control.
.OperOperReq An operator request to go to Operator control.
To determine whether an instruction is in Program or Operator control, examine
the ProgOper output. If ProgOper bit is set, the instruction is in Program
control. If ProgOper bit is cleared, the instruction is in Operator control.
Operator control takes precedence over Program control if both input request bits
are set. For example, if ProgProgReq and ProgOperReq bits are set, the
instruction goes to Operator control.
The Program request inputs take precedence over the Operator request inputs.
This provides the capability to use the ProgProgReq and ProgOperReq inputs to
lock an instruction in a desired control.
For example, assume that a Totalizer instruction is always used in Operator
control, and the user program never controls the running or stopping of the
Totalizer. In this case, wire a literal value of 1 into the ProgOperReq input. This
prevents the operator from ever putting the Totalizer into Program control by
setting the OperProgReq input from an operator interface device.
Likewise, constantly setting the ProgProgReq input can "lock" the instruction
into Program control. This is useful for automatic startup sequences when you
want the program to control the action of the instruction without an operator
inadvertently taking control of the instruction. In this example, the program sets
the ProgProgReq input during the startup, and clears the ProgProgReq input
once the startup is complete. Once the ProgProgReq input is cleared, the
instruction remains in Program control until it receives a request to change. For
18 Rockwell Automation Publication 1756-PM009E-EN-P - October 2014