82801CA Datasheet, PDF (103/521 Pages) Intel Corporation – I/O Controller Hub 3-S (ICH3-S)

Functional Description
5.6.3
5.6.4
Counter 2, Speaker Tone
This counter provides the speaker tone and is typically programmed for Mode 3 operation. The
counter provides a speaker frequency equal to the counter clock frequency (1.193 MHz) divided by
the initial count value. The speaker must be enabled by a write to port 061h (see NMI Status and
Control ports).
Timer Programming
The counter/timers are programmed in the following fashion:
1. Write a control word to select a counter
2. Write an initial count for that counter.
3. Load the least and/or most significant bytes (as required by Control Word bits 5, 4) of the
16-bit counter.
4. Repeat with other counters
Only two conventions need to be observed when programming the counters. First, for each counter,
the control word must be written before the initial count is written. Second, the initial count must
follow the count format specified in the control word (least significant byte only, most significant
byte only, or least significant byte and then most significant byte).
A new initial count may be written to a counter at any time without affecting the counter's
programmed mode. Counting will be 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.
Intel^® 82801CA ICH3-S Datasheet
103