Intel E3845 FH8065301487715 Data Sheet

 

Intel

®

 Atom™ Processor E3800 Product Family

Datasheet

4553

A new initial count may be written to a counter at any time without affecting the 
counter's programmed mode. Counting is affected as described in the mode definitions. 
The new count must follow the programmed count format.

If a counter is programmed to read/write two-byte counts, the following precaution 
applies: A program must not transfer control between writing the first and second byte 
to another routine which also writes into that same counter. Otherwise, the counter will 
be loaded with an incorrect count.

The Control Word Register at port 43h controls the operation of all three counters. 
Several commands are available:

•

Control Word Command. Specifies which counter to read or write, the operating 
mode, and the count format (binary or BCD). 

•

Counter Latch Command. Latches the current count so that it can be read by the 
system. The countdown process continues. 

•

Read Back Command. Reads the count value, programmed mode, the current 
state of the OUT pins, and the state of the Null Count Flag of the selected counter.

 lists the six operating modes for the interval counters.

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.

0

Out signal on end of count (=0) Output is 0. When count goes to 0, output goes to 1 

and stays at 1 until counter is reprogrammed.

1

Hardware re-triggerable one-
shot

Output is 0. When count goes to 0, output goes to 1 
for one clock time.

2

Rate generator (divide by n 
counter)

Output is 1. Output goes to 0 for one clock time, then 
back to 1 and counter is reloaded.

3

Square wave output

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.

4

Software triggered strobe

Output is 1. Output goes to 0 when count expires for 
one clock time.

5

Hardware triggered strobe

Output is 1. Output goes to 0 when count expires for 
one clock time.