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3
SEQUENCE PROGRAM EXECUTION
3.2 Concept of Scan Time
(1) Scan time
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3.2 Concept of Scan Time
Scan time is a period from the time when the CPU module starts the sequence
program operation from Step 0 until it executes Step 0 of the same sequence program
again.
The scan time consists of the sequence program execution time and the END
processing time.
(a) Scan time storage location
The CPU module measures the current value and minimum and maximum values
of the scan time and stores them into the special registers (SD520, SD521,
SD524 to 527).
The scan time can be checked by monitoring SD520, SD521 and SD524 to 527.
SD520
Current value
SD524
Minimum value
Maximum value
SD526
When SD520 is 3 and SD521 is 400, the scan time is 3.4ms.
(b) Accuracy and measurement of scan time
The accuracy of each scan time stored into the special registers is
(c) Scan time watch
The CPU module has scan time watch timers (watchdog timers). (
section)
SD521
SD525
SD527
Stores scan time of 1ms or less (unit s).
Stores scan time in 1ms units.
Diagram 3.6 Scan time storage location
0.1ms.
(2) in this
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