Emerson Epsilon EP Drive 400518-01 Manual de instalación Pagina 131

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119
Programming
A Dwell instruction is also a motion instruction and can block the program in the same way. The Dwell cannot start until
Index0 is complete, and therefore the program (or task) is blocked until Index0 is finished.
The Wait For instruction will block the program until the Wait For condition is satisfied. The Wait For condition does not
have to be TRUE at the exact time the task is processed. If the Wait For condition is satisfied at any time (even when that
task is not being processed) the task will be scheduled to run the next time through the loop.
Figure 95 shows the same time-slicing diagram as above, but Task 0 is blocked in this example. Notice how Task 0 is skipped
when the processor recognizes the task is blocked and processor execution switches to Task 1.
Figure 95: Block Time Slice
The time taken to process the blocked task and pass on to the next available task is between 50 and 100 microseconds.
Figure 96 is a flowchart that reflects the time-slicing process. It shows the complete loop based on whether Modbus messages
need processing and if programs (tasks) are blocked.
Blocked here until
Index0 is complete
Index.0.Initiate
Dwell For Time 1.000 'Seconds
ModuleOutput.1=ON
= Control Loop Update
= Program Execution
N = Number of Tasks assigned
= Messages (Modbus, Keypad, LCD Display, Faults, etc.)
1600 usec 1600 usec 1600 usec
= Blocked Task (Blocked Program)
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