82801DB Datasheet, PDF (325/587 Pages) Intel Corporation – Intel 82801DB I/O Controller Hub 4 (ICH4)

LPC Interface Bridge Registers (D31:F0)
9.4.1
ICW1—Initialization Command Word 1 Register
Offset Address:
Default Value:
Master Controller–020h
Slave Controller–0A0h
All bits undefined
Attribute:
Size:
WO
8 bit /controller
A write to Initialization Command Word 1 starts the interrupt controller initialization sequence,
during which the following occurs:
1. The Interrupt Mask register is cleared.
2. IRQ7 input is assigned priority 7.
3. The slave mode address is set to 7.
4. Special mask mode is cleared and Status Read is set to IRR.
Once this write occurs, the controller expects writes to ICW2, ICW3, and ICW4 to complete the
initialization sequence.
Bit
Description
ICW/OCW Select — WO. These bits are MCS-85 specific, and not needed.
7:5
000 = Should be programmed to 000
ICW/OCW Select — WO.
4
1 = This bit must be a 1 to select ICW1 and enable the ICW2, ICW3, and ICW4 sequence.
3
Edge/Level Bank Select (LTIM) — WO. Disabled. Replaced by the edge/level triggered control
registers (ELCR).
ADI — WO.
2
0 = Ignored for the Intel^® ICH4. Should be programmed to 0.
Single or Cascade (SNGL) — WO.
1
0 = Must be programmed to a 0 to indicate two controllers operating in cascade mode.
ICW4 Write Required (IC4) — WO.
0
1 = This bit must be programmed to a 1 to indicate that ICW4 needs to be programmed.
Intel^® 82801DB ICH4 Datasheet
325