SB82371 Intel Corporation, SB82371 Datasheet - Page 69

• Manufacturer Part Number: SB82371
• Description: 82371FB (PIIX) AND 82371SB (PIIX3) PCI ISA IDE XCELERATOR
• Manufacturer: Intel Corporation

2.5.2.3.
I/O Address:
Default Value:
Attribute:
Each of these I/O ports is used for writing count values to the Count Registers; reading the current count
value from the counter by either an I/O read, after a counter-latch command, or after a Read Back Command;
and reading the status byte following a Read Back Command.
2.5.3.
The PIIX/PIIX3 contains an ISA-Compatible interrupt controller that incorporates the functionality of two
82C59 interrupt controllers. The interrupt registers control the operation of the interrupt controller.
6
5:4
3:1
0
7:0
Bit
Bit
INTERRUPT CONTROLLER REGISTERS
Counter Port bit[x]. Each counter I/O port address is used to program the 16-bit Count
Register. The order of programming, either LSB only, MSB only, or LSB then MSB, is defined
with the Interval Counter Control Register. The counter I/O port is also used to read the current
count from the Count Register and return counter programming status following a Read Back
Command.
Count Register Status. This bit indicates when the last count written to the Count Register
(CR) has been loaded into the counting element (CE). 0=Count has been transferred from CR
to CE and is available for reading. 1=Count has not been transferred from CR to CE and is not
yet available for reading.
Read/Write Selection Status. Bits[5:4] reflect the read/write selection made through bits[5:4]
of the Control Register.
Bit[5:4]
00
01
10
11
Mode Selection Status. Bits[3:1] return the counter mode programming.
Bit[3:1]
000
001
X10
Countdown Type Status. 0=Binary countdown; 1=Binary coded decimal (BCD) countdown.
Counter Access Ports Register
Mode Selected
0
1
2
Counter 0—040h; Counter 1—041h; Counter 2—042h
All bits undefined
Read/Write
Function
Counter Latch Command
R/W Least Significant Byte (LSB)
R/W Most Significant Byte (MSB)
R/W LSB then MSB
Bit[3:1]
X11
100
101
Description
Description
Mode Selected
3
4
5
82371FB (PIIX) AND 82371SB (PIIX3)
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