Allen-Bradley MicroLogix 1200 Reference Manual page 101

8. The PTO instruction is DONE.
While the PTO instruction is being executed, status bits and information
are updated as the main controller continues to operate. Because the PTO
instruction is actually being executed by a parallel system, status bits and
other information are updated each time the PTO instruction is scanned
while it is running. This provides the control program access to PTO
status while it is running.
PTO status is only as fresh as the scan time of the
NOTE
controller. Worst case latency is the same as the maximum
scan of the controller. This condition can be minimized by
placing a PTO instruction in the STI (selectable timed
interrupt) file, or by adding PTO instructions to your
program to increase how often a PTO instruction is
scanned.
The charts in the following examples illustrate the typical timing
sequence/behavior of a PTO instruction. The stages listed in each chart
have nothing to do with controller scan time. They simply illustrate a
sequence of events. In actuality, the controller may have hundreds or
thousands of scans within each of the stages illustrated in the examples.
Conditions Required to Start the PTO
The following conditions must exist to start the PTO:
• The PTO instruction must be in an idle state.
• For idle state behavior, all of the following conditions must be met:
– Jog Pulse (JP) bit must be off
– Jog Continuous (JC) bit must be off
– Enable Hard Stop (EH) bit must be off
– Normal Operation (NS) bit must be off
– The output cannot be forced
• The rung it is on must transition from a False state (0) to a True state
(1).
Using High-Speed Outputs 6-3
Publication 1762-RM001C-EN-P