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5 BASIC USAGE
5 - 6
(a) The ring counter will operate as follows when the "present value < ring
counter minimum value" or "ring counter maximum value < present value".
• For up 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 addition
pulse, (ring counter maximum value +1) will be stored as the present
value.
• For down count
When the present value reaches the ring counter maximum value, the ring
counter minimum value is automatically stored as the present value.
Whether during up count or down count, the ring counter maximum value
will not be stored in the buffer memory for storing the present values.
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 3000,
the count range and present value will change as shown in the figure below.
– 2147483648
Count range
Present value
3001
3000
to
2147483647 –2147483648
(b) When the "ring counter's minimum value is equal to the ring counter's
maximum value", the count range will cover any value that can be expressed
in 32-bit signed binary values (-2147483648 to +2147483637), regardless of
the present value.
POINTS
(1) When the count enable command {Y04(Y0C)} is ON, the set values for the
buffer memory will not change even if values are written as the minimum value
and maximum value of the ring counter. To change the ring counter maximum
and minimum value settings, first turn the count enable command OFF.
(2) When the count range is to be changed using preset, always change it after
first turning the count enable command {Y04(Y0C)} OFF.
Ring counter minimum value
0
Ring counter
minimum value
– 1
to
– 2
MELSEC-Q
Ring counter maximum value
2000
Present value
3000
2147483647
Count range
Ring counter
maximum value
(2000)
0
to
2001
2002
The ring counter maximum value,
2000, will not be stored in the buffer
memory for storing the present values.
2998
2999
5 - 6
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