Program Flow Control Instructions used to control the sequence in which your program is executed.
Control instructions allow you to change the order in which the processor scans a ladder program.
Typically, these instructions are used to
Labels have the format Q:NNN. NNN is a numeric value from 000-255.
Jumping forward to a label saves program scan time by omitting a program segment until needed.
Jumping backward lets the controller execute program segments repeatedly.
The JMP instruction causes the controller to skip rungs. You can jump to the same label from one or more JMP instruction.
Also Read: PLC Example with JMP Instruction
This input instruction is the target of JMP instructions having the same label number.
You must program this instruction as the first instruction of a rung. This instruction has no control bits.
You can program multiple jumps to the same label by assigning the same label number to multiple JMP instructions. However, label numbers must be unique.
Note –
Do not jump (JMP) into an MCR zone. Instructions that are programmed within the MCR zone starting at the LBL instruction and ending at the ‘END MCR’ instruction are always evaluated as though the MCR zone is true, regardless of the true state of the “Start MCR” instruction.
If you use the SBR instruction, the SBR instruction must be the first instruction on the first rung in the program file that contains the subroutine.
Use a subroutine to store recurring sections of program logic that must be executed from several points within your application program.
A subroutine saves memory because you program it only once.
Update critical I/O within subroutines using immediate input and/or output instructions (IIM, IOM), especially if your application calls for nested or relatively long subroutines.
Otherwise, the controller does not update I/O until it reaches the end of the main program (after executing all subroutines).
Outputs controlled within a subroutine remain in their last state until the subroutine is executed again.
MCR zones let you enable or inhibit segments of your program, such as for recipe applications.
When you program MCR instructions, note that:
Use MCR instructions in pairs to create program zones that turn off all the non-retentive outputs in the zone.
The MCR instruction is not a substitute for a hard-wired master control relay that provides emergency stop capability.
Also Read: PLC Example with MCR Zone
Do not jump (JMP) into an MCR zone.
If you start instructions such as timers or counters in an MCR zone, instruction operation ceases when the zone is disabled.
The TOF timer activates when placed inside of a false MCR zone.
The TND instruction, when its rung is true:
If this instruction’s rung is false, the processor continues the scan until the next TND instruction or the END statement.
Use this instruction to progressively debug a program, or conditionally omit the balance of your current program file or subroutines
When the SUS instruction is executed, it causes the processor to enter the Suspend Idle mode and stores the Suspend ID in word 7 (S:7) of the status file.
All outputs are de-energized.
Use the SUS instruction to trap and identify specific conditions for program debugging and system troubleshooting.
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