Appendix A 8524 Counter Chip Functions 59
Counter Latch Operation
Users often want to read the value of a counter without disturbing the
count in progress. You do this by latching the count value for the
specific counter then reading the value.
The 82C54 supports the counter latch operation in two ways. The first
way is to set bits RW1 and RW0 to 0. This latches the count of the
selected counter in a 16-bit hold register. The second way is to
perform a latch operation under the read-back command. Set bits SC1
and SC0 to 1 and CNT = 0. The second method has the advantage of
operating several counters at the same time. A subsequent read
operation on the selected counter will retrieve the latched value.