
82801AA and 82801AB Datasheet
8-35
LPC Interface Bridge Registers (D31:F0)
8.4.5
ICW3—Slave Controller Initialization Command Word 3
Register
Offset Address:
Default Value:
A1h
All bits undefined
Attribute:
Size:
WO
8 bits
8.4.6
ICW4—Initialization Command Word 4 Register
Offset Address:
Master Controller
–
021h
Slave Controller
–
0A1h
Attribute:
Size:
WO
8 bits
8.4.7
OCW1—Operational Control Word 1 (Interrupt Mask)
Register
Offset Address:
Default Value:
Master Controller
–
021h
Slave Controller
–
0A1h
00h
Attribute:
Size:
R/W
8 bits
Bit
Description
7:3
Reserved. Must be 0.
2:0
Slave Identification Code.
These bits are compared against the slave identification code broadcast
by the master controller from the trailing edge of the first internal INTA# pulse to the trailing edge of
the second internal INTA# pulse. These bits must be programmed to 02h to match the code
broadcast by the master controller. When 02h is broadcast by the master controller during the INTA#
sequence, the slave controller assumes responsibility for broadcasting the interrupt vector.
Bit
Description
7:5
Reserved. Must be 0.
4
Special Fully Nested Mode (SFNM).
Should normally be disabled by writing a 0 to this bit. If
SFNM=1, the special fully nested mode is programmed.
3
Buffered Mode (BUF).
Must be programmed to 0 for the ICH. This is non-buffered mode.
2
Master/Slave in Buffered Mode.
Not used. Should always be programmed to 0.
1
Automatic End of Interrupt (AEOI).
This bit should normally be programmed to 0. This is the normal
end of interrupt. If this bit is 1, the automatic end of interrupt mode is programmed. AEOI is discussed
in Section 16.10.2.
0
Microprocessor Mode.
This bit must be programmed to 1 to indicate that the controller is operating
in an Intel Architecture-based system. Programming this bit to 0 results in improper controller
operation.
Bit
Description
7:0
Interrupt Request Mask.
When a 1 is written to any bit in this register, the corresponding IRQ line is
masked. When a 0 is written to any bit in this register, the corresponding IRQ mask bit is cleared, and
interrupt requests are again accepted by the controller. Masking IRQ2 on the master controller also
masks the interrupt requests from the slave controller.