Datasheet
ACPI Devices
Intel
®
Atom™ Processor E6xx Series Datasheet
202
There are two special commands that can be issued to the counters through this
register, the Read Back Command and the Counter Latch Command. When these
commands are chosen, several bits within this register are redefined. These register
formats are described below.
11.1.5.1 Read Back Command
This 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.
Table 298. 43h: TCW - Timer Control Word Register
Size: 8 bit Default: Undefined Power Well: Core
Fixed IO Address: 43h
Bit Range Default Access Acronym Description
07 :06 Undef WO CS
Counter Select: The Counter Selection bits select the counter the
control word acts upon as shown below. The Read Back Command is
selected when bits[7:6] are both 1.
00 = Counter 0 select
01 = Counter 1 select
10 = Counter 2 select
11 = Read Back Command
05 :04 Undef WO RWS
Read/Write Select: The counter programming is done through the
counter port (40h for counter 0, 41h for counter 1, and 42h for counter
2)
00 = Counter Latch Command
01 = Read/Write Least Significant Byte (LSB)
10 = Read/Write Most Significant Byte (MSB)
11 = Read/Write LSB then MSB
03 :01 Undef WO CMS
Counter Mode Selection: Selects one of six modes of operation for the
selected counter.
000 = Out signal on end of count (=0)
001 = Hardware retriggerable one-shot
x10 = Rate generator (divide by n counter)
x11 = Square wave output
100 = Software triggered strobe
101 = Hardware triggered strobe
00 Undef WO BCS
Binary/BCD Countdown Select:
0 = Binary countdown is used. The largest possible binary count is 2
16
1 = Binary coded decimal (BCD) count is used. The largest possible BCD
count is 10
4