Intel 460GX Software Developer’s Manual page 212

LPC/FWH Interface Configuration
11.2.2.4 Icw3–Initialization Command Word 3 Register (I/O)
I/O Address:
Default Value:
Attribute:
On CNTRL-2 (the slave controller), ICW3 is the slave identification code broadcast by CNTRL-1.
Bit
7:3
2:0
11.2.2.5 Icw4–Initialization Command Word 4 Register (I/O)
I/O Address:
Default Value:
Attribute:
Both IFB interrupt controllers must have ICW4 programmed as part of their initialization
sequence.
Bit
7:5
4
3
2
1
0
11.2.2.6 Ocw1–Operational Control Word 1 Register (I/O)
I/O Address:
Default Value:
Attribute:
OCW1 sets and clears the mask bits in the Interrupt Mask Register (IMR). Each interrupt request
line may be selectively masked or unmasked any time after initialization. The IMR stores the
interrupt line mask bits. The IMR operates on the IRR. Masking of a higher priority input does not
affect the interrupt request lines of lower priority. Unlike status reads of the ISR and IRR, for
reading the IMR, no OCW3 is needed. The output data bus contains the IMR when an I/O read is
active and the I/O address is 021h or 0A1h (OCW1). All writes to OCW1 must occur following the
ICW1-ICW4 initialization sequence, since the same I/O ports are used for OCW1, ICW2, ICW3
and ICW4.
11-22
INT CNTRL-2–0A1h
All bits undefined
Write Only
Reserved. Must be programmed to all 0s.
Slave Identification Code. Must be programmed to 02h.
INT CNTRL-1–021h; INT CNTRL-2–0A1h
01h
Write Only
Reserved. Must be programmed to all 0s.
Special Fully Nested Mode (SFNM). Bit 4, SFNM, should normally be disabled by writing a 0
to this bit. If SFNM=1, the special fully nested mode is programmed.
Buffered mode (BUF). Must be programmed to 0 selecting non-buffered mode.
Master/Slave in Buffered Mode. Should always be programmed to 0. Bit not used.
AEOI (Automatic End of Interrupt). 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.
Microprocessor Mode. Must be programmed to 1 indicating an Intel Architecture-based
system.
INT CNTRL-1–021h; INT CNTRL-2–0A1h
00h
Read/Write
Description
Description
Intel® 460GX Chipset Software Developer's Manual