Counter Operations - Advantech MIC-3716 Manual

D.4 Counter Operations
Read/Write Operation
Before you write the initial count to each counter, you must first
specify the read/write operation type, operating mode and counter type
in the control byte and write the control byte to the control register
[BASE + 30(Dec)].
Since the control byte register and all three counter read/write
registers have separate addresses and each control byte specifies the
counter it applies to (by SC1 and SC0), no instructions on the
operating sequence are required. Any programming sequence
following the 82C54 convention is acceptable.
There are three types of counter operations: Read/load LSB, read /load
MSB and read /load LSB followed by MSB. It is important that you
make your read/write operations in pairs and keep track of the byte
order.
Counter Read-back Command
The 82C54 counter read-back command lets you check the count
value, programmed mode and current states of the OUT pin and Null
Count flag of the selected counter(s). You write this command to the
control word register. The format is as shown at the beginning of this
section. The read-back command can latch multiple counter output
latches. Simply set the CNT bit to 0 and select the desired counter(s).
This single command is functionally equivalent to multiple counter
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