Allen-Bradley LOGIX 5000 Reference Manual page 458

Chapter 7 Equipment Phase Instructions
458
Structured Text
None
Enter the parentheses ( ) after the instruction mnemonic, even though there are no
operands.
Guidelines for using the PPD Instruction
Guideline
Organize logic as a series of steps.
Do not use a PPD instruction as a temporary
end of the routine.
Use PPD instruction to pause at the same
breakpoint over several scans.
Make sure only 1 PPD instruction at a time is
true.
Choose the substate to use.
Affects Math Status Flags
No
Rockwell Automation Publication 1756-RM006K-EN-P - November 2018
Details
PPD instructions (breakpoints) are easiest to use if the logic moves through
defined steps, such as a state machine or SFC.
• A breakpoint only signals that specific conditions are met. It does
not stop the execution of the equipment phase.
• To have logic actually break (pause) at a breakpoint, organize the logic
so that it stays at the step at which the breakpoint occurred until it
receives the resume command.
Even when an equipment phase pauses, it continues to execute all its logic.
• When a PPD instruction executes, it only sets the Paused bit for the
equipment phase.
• If programing the PPD instruction in RLL, it disables only the rest of the
logic on its rung. It does not terminate or suspend the execution of the
routine.
• Think of the PPD instruction as a condition that applies or is ignored
based on the auto pause and pause commands.
When the PauseEnabled bit is TRUE, an equipment phase goes to Paused at
the first PPD instruction whose conditions are true. If the PPD instruction
executes over several scans, the equipment phase may continually pause at
the same breakpoint.
A PPD instruction does not have a control tag to remember whether it
executed.
• Anytime its conditions are true (and the equipment phase is in a
substate with PauseEnabled True), the PPD instruction acts as a
breakpoint (and pauses the phase by disabling the rest of the logic on
the rung).
• Limiting logic to one possible breakpoint at a time ensures a pause at
the required breakpoint.
PPD instructions (breakpoints) work only when the equipment phase
PauseEnabled bit is True.
To pause at:
Each true breakpoint
First true breakpoint
Give this command:
Auto Pause
Pause