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3.2 Concept of Scan Time

SEQUENCE PROGRAM EXECUTION

3.2 Concept of Scan Time

(1) 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.

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 0.1ms.

The CPU module has scan time watch timers (watchdog timers). ( (2) in this

section)

Diagram 3.6 Scan time storage location

Stores scan time of 1ms or less (unit s).

Stores scan time in 1ms units.

SD520

SD524

SD526

Current value

Minimum value

Maximum value

SD521

SD525

SD527

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