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MELSEC-Q
5 BASIC USAGE
5.2.2 Selecting the ring counter
(1) Ring counter operation
This function repeatedly counts pulses between the range specified in CH Ring
counter minimum value (Un\G20, Un\G21, Un\G52, Un\G53) and CH
Ring
counter maximum value (Un\G22, Un\G23, Un\G54, Un\G55).
When the ring counter is being selected, an overflow error does not occur.
The ring counter can be used in combination with the preset function and the
coincidence output function.
+2147483647
CH Ring counter maximum value (Un\G22, Un\G23, Un\G54, Un\G55)
CH Ring counter minimum value (Un\G20, Un\G21, Un\G52, Un\G53)
-2147483648
Present counter value
Count up
Count down
0
(2) Ring counter count range
The count range of the ring counter is determined by the relationship between
CH
Present value (Un\G2, Un\G3, Un\G34, Un\G35) and the ring counter
lower/upper limits when CH
Count enable command (Y4, YC) is turned on or
when the preset function is performed.
Normally the range used is "ring counter minimum value ≤
present value ≤ ring
counter maximum value".
• For up count
When the present value reaches the ring counter maximum value, the ring
counter minimum value is automatically stored as the present value.
• For down count
Even if the present value reaches the ring counter minimum value, the ring
counter minimum value will be retained as is. With the next subtraction pulse,
(ring counter maximum value -1) will be stored as the present value.
In counting up and down, the ring counter upper limit value is not stored in CH
Present value (Un\G2, Un\G3, Un\G34, Un\G35).
For example, if the count is enabled with the ring counter minimum value of 0, the
ring counter maximum value of 2000 and the present value of 500, the count
range and present value will change as shown in the figure below.
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Ring counter minimum value
Present value
Ring counter maximum value
0
500
2000
2147483647
Ring counter
minimum value
(2000)
Present value
500 501 1998 1999to 0 1 2 to 498 499
Counting range
Ring counter
maximum value
Ring counter maximum value,
2000 is not stored in CH Present
value
(Un\G2, Un\G3, Un\G34, Un\G35).