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COUNTERS
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Area in Memory :
Counters have an area reserved for them in the memory of your CPU. This memory area
reserves one 16-bit word for each counter address. The ladder logic instruction set
supports 256 counters. The counter instructions are the only functions that have access
to the counter memory area.
Count Value:
Bits 0 through 9 of the counter word contain the count value in binary code. The count
value is moved to the counter word when a counter is set. The range of the count value
is 0 to 999. You can vary the count value within this range by using the following
counter instructions:

2. If I0.1 changes from "0" to "1", the counter is preset with the value at PV (10 in
the above figure). If the signal state of I0.0 changes from "0" to "1", the value of
counter C10 will be incremented by one - unless the value of C10 is equal to
"999". Q4.0 is "1" if C10 is not equal to zero.
If I0.1 changes from "0" to "1", the counter is preset with the value at PV (20 in
the above figure). If the signal state of I0.0 changes from "0" to "1", the value of
counter C10 will be decremented by one - unless the value of C10 is equal to "0".
Q4.0 is "1" if C10 is not equal to zero.

3. If I0.2 changes from "0" to "1", the counter is preset with the value at PV (20 in
the above figure). If the signal state of I0.0 changes from "0" to "1", the value of
counter C10 will be incremented by one - except when the value of C10 is equal
than "999". If I0.1 changes from "0" to "1", C10 is decremented by one - except
when the value of C10 is equal to "0". Q4.0 is "1" if C10 is not equal to zero.

4. If the signal state of input I0.0 changes from "0" to "1" (positive edge in RLO), the
preset value of 100 is loaded to counter C10. If the signal state of input I0.1
changes from "0" to "1" (positive edge in RLO), counter C10 count value will be
incremented by one unless the value of C10 is equal to "999". If there is no
positive edge in RLO, the value of C10 will be unchanged.
If the signal state of I0.2 is "1", the counter C10 is reset to "0".

5. If the signal state of input I0.0 changes from "0" to "1" (positive edge in RLO), the
present value of 100 is loaded to counter C10. If the signal state of input I0.1
changes from "0" to "1" (positive edge in RLO), counter C10 count value will be
decremented by one unless the value of C10 is equal to "0". If there is no positive
edge in RLO, the value of C10 will be unchanged. If the count value = 0, then
Q4.0 is turned on.
If the signal state of input I0.2 is "1", the counter C10 is reset to "0".