MELSEC-A
8. EXECUTING THE RING COUNTER FUNCTION
8 - 4
8.1.2 Count range
As shown below, the count range of the ring counter function differs depending on the
relationship between the preset value, ring counter value, present value and counting
mode (up/down count).
(1) If preset value
present value ring counter value
The following operation is performed if the ring counter function is executed at the
preset value of 0, ring counter value of 2000, and present value of 500.
1) In up count, the present value returns to the preset value (0) as soon as it is
counted up to the ring counter value (2000)
500
501 1998
1999
2000/0
1 2 3to
2) In down count, the present value returns to the maximum value (16777215)
when it is counted down to the preset value (0).
Then, when the present value is counted down to the ring counter value (2000),
it returns to the preset value(0).
500
499 0
16777215
2002
2001
2000/0
16777215
to to
(2) If preset value
ring counter value present value
The following operation is performed if the ring counter function is executed at the
preset value of 0, ring counter value of 2000, and present value of 3000.
1) In up count, the present value returns to the minimum value (0) when it is
counted up to the maximum value (16777215).
Then, when the present value is counted up to the ring counter value (2000), it
returns to the preset value(0).
3000 3001 16777215 0
1999
2000/0 1 2
to
2) In down count, the present value returns to the preset value (0) as soon as it is
counted down to the ring counter value (2000).
3000 2999 2001 2000/0
16777215
16777214 16777213
16777212
to
POINT
• Do not write the preset and ring counter values during execution of the ring
counter function. If they are written, the ring counter operation may not be
performed properly.
• Note that the ring counter function is not activated when the following
expression is satisfied.
Ring counter cycle
10-link scan time+2-sequence scan time
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