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6 CONVENIENT USAGE
6.1.1 Reading the counter function selection count value
6
6 - 2
The counter function selection count values are stored when the counter function
selection is executed. The count values when the latch counter, sampling counter and
periodic pulse counter functions are executed are stored in the counter function
selection count value storage buffer memory at the addresses shown in the table
below.
Present
Contents
value
Buffer
CH1
2
to 3
H
memory
CH2 22
to 23
H
address
The present values and counter function selection count values are stored as 32-bit
signed binary values in the buffer memory. Also, since the contents of the buffer
memory are automatically updated by the count operation, the latest count values can
be read from the buffer memory.
POINT
(1) When reading the present and counter function selection count values, use the
DFRO command and always read values in two-word units. When reading
values in one-word units, if the count values are updated in the middle of read
processing, a mismatch may occur between the data contents of the lower and
higher words, possibly causing the system to read incorrect count values.
[Program example]
X20
[Example of an undesirable program]
X20
(2) Although the latch count value and present periodic pulse count value are
stored in different addresses, the same values are always stored (updated at
the same time). Thus, when the latch counter function or periodic pulse
counter function is executed, the present periodic pulse count value and latch
count value do not retain their previous values.
Counter function selection count value
Latch count
Sampling
value
count value
C
to D
E
to F
H
H
H
H
2C
to 2D
2E
to 2F
H
H
H
H
DFRO
H00
H0E
FROM
H00
H0F
FROM
H00
H0E
MELSEC-Q
Periodic pulse
Periodic pulse
count previous
count present
value
value
10
to 11
12
to 13
H
H
H
H
30
to 31
32
to 33
H
H
H
H
D0
K1
D1
K1
D0
K1
6 - 2
H
H
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