Constant Scan - Mitsubishi Electric MELSEC-Q Series User Manual

7 FUNCTION

7.2 Constant Scan

(1) What is Constant Scan?
Scan time when constant scan is not used
Scan time when constant scan setting is set to 7 ms
7 - 2
The scan time differs because the processing time differs depending on whether
the instruction, which is used in the sequence program, is executed or not.
Constant scan is a function to execute the sequence program repeatedly while
maintaining the scan time at a constant time.
The I/O refresh is executed before the sequence program is executed. So the
I/O refresh stays constant even when the execution time of the sequence
program varies.
END 0
5ms
END 0 END
Wait time
5ms
7ms
Fig. 7.1 Constant scan operation
Sequence program
END processing
END 0 END 0
6ms
Sequence program
END processing
0 END 0
2ms 6ms 1ms
7ms
MELSEC-Q
END 0
5ms
END 0
5ms 2ms
7ms
7 - 2
7