82NM10 Datasheet, PDF (111/671 Pages) Intel Corporation – Intel® NM10 Family Express Chipset

Functional Description
Table 5-40.Counter Operating Modes
3
Square wave output
4
Software triggered strobe
5
Hardware triggered strobe
Output is 1. Output goes to 0 when counter rolls
over, and counter is reloaded. Output goes to 1
when counter rolls over, and counter is reloaded,
etc.
Output is 1. Output goes to 0 when count expires
for one clock time.
Output is 1. Output goes to 0 when count expires
for one clock time.
5.8.2
5.8.2.1
Note:
5.8.2.2
Reading from the Interval Timer
It is often desirable to read the value of a counter without disturbing the count in
progress. There are three methods for reading the counters: a simple read operation,
counter Latch command, and the Read-Back command. Each is explained below.
With the simple read and counter latch command methods, the count must be read
according to the programmed format; specifically, if the counter is programmed for two
byte counts, two bytes must be read. The two bytes do not have to be read one right
after the other. Read, write, or programming operations for other counters may be
inserted between them.
Simple Read
The first method is to perform a simple read operation. The counter is selected through
port 40h (counter 0), 41h (counter 1), or 42h (counter 2).
Performing a direct read from the counter does not return a determinate value,
because the counting process is asynchronous to read operations. However, in the case
of counter 2, the count can be stopped by writing to the GATE bit in port 61h.
Counter Latch Command
The Counter Latch command, written to port 43h, latches the count of a specific
counter at the time the command is received. This command is used to ensure that the
count read from the counter is accurate, particularly when reading a two-byte count.
The count value is then read from each counter’s Count register as was programmed by
the Control register.
The count is held in the latch until it is read or the counter is reprogrammed. The count
is then unlatched. This allows reading the contents of the counters on the fly without
affecting counting in progress. Multiple Counter Latch Commands may be used to latch
more than one counter. Counter Latch commands do not affect the programmed mode
of the counter in any way.
If a Counter is latched and then, some time later, latched again before the count is
read, the second Counter Latch command is ignored. The count read is the count at the
time the first Counter Latch command was issued.
Datasheet
111