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DMx820 User’s Manual
Bit D7 indicates the status of the output pin. Use of this bit makes it possible to monitor the counter output, so the corresponding hardware may
be omitted.
Null count indicates the count value finally written in the counter register (CR) has been loaded in the counter element (CE). The time when the
count value was loaded in the CE depends on the mode of each counter, and it cannot be known by reading the counter value because the
count value does not tell the new count value if the counter is latched. The null count operation is shown below.
Operation
Result
A. Control word register writing
Null count = 1
B. Count register (CR) writing
Null count = 1
C. New count loading to CE (CR->CE)
Null count = 0
Note: The null count operation for each counter is independent. When the 2-byte count is programmed, the null count is set to
1 when the count value of the second byte is written.
If status latching is carried out multiple times before status reading, other than the first status latch is ignored.
Simultaneous latching of the count and status of the selected counter is also possible. For this purpose, set bits D4 and D3, COUNT and
STATUS bits, to 00. This is functionally the same as writing two separate read back commands at the same time. If counter/status latching is
carried out multiple times before each reading, other than the first one is ignored here again. The example is shown below.