LPC Interface Bridge Registers (D31:F0)
9-30
Intel
82801BA ICH2 Datasheet
9.3
Timer I/O Registers
9.3.1
TCW—Timer Control Word Register
I/O Address:
Default Value:
43h
All bits undefined
Attribute:
Size:
WO
8 bits
This register is programmed prior to any counter being accessed to specify counter modes.
Following part reset, the control words for each register are undefined and each counter output is 0.
Each timer must be programmed to bring it into a known state.
Port
Aliases
Register Name/Function
Default Value
Type
40h
50h
Counter 0 Interval Time Status Byte Format
0XXXXXXXb
RO
Counter 0 Counter Access Port Register
Undefined
R/W
41h
51h
Counter 1 Interval Time Status Byte Format
0XXXXXXXb
RO
Counter 1 Counter Access Port Register
Undefined
R/W
42h
52h
Counter 2 Interval Time Status Byte Format
0XXXXXXXb
RO
Counter 2 Counter Access Port Register
Undefined
R/W
43h
53h
Timer Control Word Register
Undefined
WO
Timer Control Word Register Read Back
XXXXXXX0b
WO
Counter Latch Command
X0h
WO
Bit
Description
7:6
Counter Select
—WO. 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
5:4
Read/Write Select
—WO. These bits are the read/write control bits. The actual 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
3:1
Counter Mode Selection
—WO. These bits select one of six possible modes of operation for the
selected counter.
000 = Mode 0
Out signal on end of count (=0)
001 = Mode 1
Hardware retriggerable one-shot
x10 = Mode 2
Rate generator (divide by n counter)
x11 = Mode 3
Square wave output
100 = Mode 4
Software triggered strobe
101 = Mode 5
Hardware triggered strobe
0
Binary/BCD Countdown Select
—WO.
0 = Binary countdown is used. The largest possible binary count is 216
1 = Binary coded decimal (BCD) count is used. The largest possible BCD count is 104
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