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4.A2CCPU
- - - - - - - - - - - - - - - - - - - - MELSEC-A
I
4.2.1
Constant scan
Because the processing time of each individual instruction in a sequence
program differs depending on whether or not the instruction is executed, the
scan time differs accordingly for each scan.
The constant scan function sets such varying scan times to a fixed value
regardless of the sequence program processing time.
Scan time - constant scan function Is not used
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Sequence program
~ ~
END processing
END
o
END
0
END
0
END
0
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I'
I
I
I
I
. I
f-----
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50 msec
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60 msec
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50 msec
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Scan time - constant scan function Is fixed to 70 msec
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Sequence program
~
END processing
END
o
END
/
0
END
0
END
0
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I'
I'~
- ' I
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~
--+------1
~--+-
Wait
~
60 msec
10
mslec
20 m ec
50 msec
50
mS80
70 msec
20 rnsec
70 msec
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70 msec
T
Fig. 4.11 Constant Scan Function
(1)
Setting range
(a) Constant scan time can be set in the range of 10 msec to 2000 msec.
Enter the required constant scan time to special register D9020 in
units of 10 msec (setting value between 10 and 2000).
If D9020 is set outside the range of 1 msec to 200 msec, the constant
scan time will be set as indicated below.
Setting for D9020
Constant Scan Time
-32768 to 0
Not set
1 to 200
10 msec to 2000 msee
201 to 32767
2000 msec
4-19

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