Logix5000 Controllers General Instructions - SLAC Confluence

Function Block Attributes 657Likewise, constantly setting the ProgProgReq can “lock” the instructioninto Program control. This is useful for automatic startup sequenceswhen you want the program to control the action of the instructionwithout worrying about an operator inadvertently taking control of theinstruction. In this example, you have the program set theProgProgReq input during the startup, and then clear the ProgProgReqinput once the startup was complete. Once the ProgProgReq input iscleared, the instruction remains in Program control until it receives arequest to change. For example, the operator could set theOperOperReq input from a faceplate to take over control of thatinstruction. The following example shows how to lock an instructioninto Program control.When StartupSequenceActiveis set, the PIDE instruction isplaced in Program control andManual mode. The StartupCVvalue is used as the loop output.Operator request inputs to an instruction are always cleared by theinstruction when it executes. This allows operator interfaces to workwith these instructions by merely setting the desired mode request bit.You don’t have to program the operator interface to reset the requestbits. For example, if an operator interface sets the OperAutoReq inputto a PIDE instruction, when the PIDE instruction executes, itdetermines what the appropriate response should be and clears theOperAutoReq.Publication 1756-RM003I-EN-P - January 2007