Emerson EZMotion User Manual page 183

passed on to the next task. The following program instructions will cause a program to be blocked:
Index.#.Initiate
Home.#.Initiate
Jog.#.PlusInitiate
Jog.#.MinusInitiate
Dwell For Time
Dwell For Master Dist
Wait For Time
Wait For (XXXX)
The motion instructions block processing only if they attempt to initiate motion on a profile that is already performing a motion
profile. For instance, if a program initiates Index0 and the next program instruction initiates Index1. The program will be
blocked until Index0 is complete because Index1 cannot start until motion on that profile is finished.
Index.0.Initiate
Index.1.Initiate
EZOutput.2 = ON
A Dwell instruction is also a motion instruction and can block the program in the same way.
Index.0.Initiate
Dwell For Time 0.550 'sec
EZOutput.2 = ON
The Dwell cannot start until other motion on the same profile 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 173 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.
Control Loop Update
User Program Execution
Figure 173:
The time taken to process the blocked task and pass on to the next available task is between 50 and 100 microseconds.
Figure 174 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.
EZMotion User/Programming Guide
Revision A8
Messages
Update Rate
Time Slicing Diagram (Task 0 blocked)
www.controltechniques.com
T1 T2 T3 T4
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