82801CA Datasheet, PDF (306/521 Pages) Intel Corporation – I/O Controller Hub 3-S (ICH3-S)

LPC I/F Bridge Registers (D31:F0)
9.3.1.1
9.3.1.2
RDBK_CMD—Read Back Command
The Read Back Command is used to determine the count value, programmed mode, and current
states of the OUT pin and Null count flag of the selected counter or counters. Status and/or count
may be latched in any or all of the counters by selecting the counter during the register write. The
count and status remain latched until read, and further latch commands are ignored until the count
is read. Both count and status of the selected counters may be latched simultaneously by setting
both bit 5 and bit 4 to 0. If both are latched, the first read operation from that counter returns the
latched status. The next one or two reads, depending on whether the counter is programmed for one
or two byte counts, returns the latched count. Subsequent reads return an unlatched count.
Bit
Description
7:6 Read Back Command. Must be “11” to select the Read Back Command.
Latch Count of Selected Counters.
5 _{0 = Current count value of the selected counters will be latched.}
1 = Current count will not be latched.
Latch Status of Selected Counters.
4 _{0 = Status of the selected counters will be latched.}
1 = Status will not be latched.
3
Counter 2 Select.
1 = Counter 2 count and/or status will be latched.
2
Counter 1 Select.
1 = Counter 1 count and/or status will be latched.
1
Counter 0 Select.
1 = Counter 0 count and/or status will be latched.
0 Reserved. Must be 0.
LTCH_CMD—Counter Latch Command
The Counter Latch Command latches the current count value. This command is used to insure that
the count read from the counter is accurate. The count value is then read from each counter's count
register through the Counter Ports Access Ports Register (40h for counter 0, 41h for counter 1, and
42h for counter 2). The count must be read according to the programmed format, i.e., 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 the reads). If a counter is latched once and then latched again before the count is read, the
second Counter Latch Command is ignored.
Bit
Description
Counter Selection. These bits select the counter for latching. If “11” is written, then the write is
interpreted as a read back command.
7:6 ^{00 = Counter 0}
01 = Counter 1
10 = Counter 2
Counter Latch Command.
5:4
00 = Selects the Counter Latch Command.
3:0 Reserved. Must be 0.
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Intel^® 82801CA ICH3-S Datasheet