Mitsubishi Electric MELSEC iQ-R Series Programming Manual page 29

■Program block with the same execution cycle and phase
When multiple program blocks are set to be executed in the same phase, the program blocks are executed in the order set on
the "Program File Setting" window of the engineering tool.
Ex.
Fixed period execution of program blocks with the same execution cycle and phase
800ms
200ms 200ms 200ms
#1 #2 #3
A
B
C
Although the program blocks B and C have the same cycle and phase, the program block B is executed first in accordance with the execution order.
■Synchronizing phases in different execution cycles
The normal-speed program block is executed once when the high-speed program block is executed for "Normal-speed
execution cycle  High-speed execution cycle" times. The low-speed program block is executed once when the high-speed
program block is executed for "Low-speed execution cycle  High-speed execution cycle" times.
For example, when the execution cycle of high-speed program block is 100ms and that of normal-speed program block is
500ms, the normal-speed program block is executed once when the high-speed program block is executed five times.
Therefore, if the scan time exceeds 100ms, each program block cannot be executed in the setting cycle.
For example, when the execution cycle of normal-speed program block is 500ms and the scan time is 150ms, the high-speed
program block is executed every 150ms. In this case, the normal-speed program block is executed once when the high-speed
program block is executed five times. Consequently, the execution cycle of normal-speed program block is 750ms, and an
error of 250ms (750ms - 500ms) will occur. Therefore, the scan time must be set to 100ms or shorter.
■Phase at operation change of the CPU module
A program is executed from the first phase when:
• CPU module is reset.
• CPU module is powered off and on.
• Operating status of the CPU module is switched from STOP to RUN.
800ms
200ms 200ms 200ms
#4 #1 #2
800ms
200ms 200ms
#3 #4
1 PROCESS CONTROL FUNCTION BLOCK
1.5 Program Execution Control
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