Rockwell Automation 1794-Lxxxx PhaseManager - Manual (Page 94)

94 Publication LOGIX-UM001B-EN-P - April 2010
Appendix A Equipment Phase Instructions (PSC, PCMD, POVR, PFL, PCLF, PXRQ, PRNP, PPD, PATT, PDET)
Guidelines for Using Breakpoints
Arithmetic Status Flags: not affected
Fault Conditions: none
Guideline Details
Organize your logic as a series of
steps. PPD instructions (breakpoints) are easiest to use if your 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 your logic actually break (pause) at a breakpoint, organize your logic so that it
stays at the step at which the breakpoint occurred until you give the resume command.
See the examples on page 96 .
Do not use a PPD instruction as a
temporary end of the routine. Even when an equipment phase is paused, it continues to execute all its logic.
• When a PPD instruction executes, it only sets the Paused bit for the equipment phase.
• If you program 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 you can apply or ignore based on the auto
pause and pause commands.
Limit the execution of a PPD
instruction to a single scan. In the pausing substate, 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. (This is different than a One Shot (ONS)
instruction, which executes only on a false-to-true transition.)
Make sure only 1 PPD instruction
at a time is true. 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 the pausing substate), the
PPD instruction acts as a breakpoint (sets the equipment phase to paused).
• Limiting your logic to one possible breakpoint at a time ensures that you pause at the
required breakpoint.
❑ Choose the correct substate. PPD instructions (breakpoints) work only when the equipment phase is in the pausing
substate:
To pause at Give this command Notes
each true
breakpoint auto pause • When you start the equipment phase, it
goes to the pausing substate.
• When you give the resume command after a
pause, the equipment phase remains in the
pausing substate.
• To turn off auto pause, give the auto pause
command again.
first true
breakpoint pause • Give the pause command after you start the
equipment phase.
• To pause at another breakpoint, give the
resume command and then the pause
command.