82801DB Datasheet, PDF (106/587 Pages) Intel Corporation – Intel 82801DB I/O Controller Hub 4 (ICH4)

Functional Description
5.7
8259 Interrupt Controllers (PIC) (D31:F0)
The ICH4 incorporates the functionality of two 8259 interrupt controllers that provide system
interrupts for the ISA compatible interrupts. These interrupts are: system timer, keyboard
controller, serial ports, parallel ports, floppy disk, IDE, mouse, and DMA channels. In addition,
this interrupt controller can support the PCI based interrupts, by mapping the PCI interrupt onto the
compatible ISA interrupt line. Each 8259 core supports eight interrupts, numbered 0–7. Table 5-14
shows how the cores are connected.
.
Table 5-14. Interrupt Controller Core Connections
8259
Master
Slave
8259
Input
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
Typical Interrupt
Source
Connected Pin / Function
Internal
Keyboard
Internal Timer / Counter 0 output
IRQ1 via SERIRQ
Internal
Slave Controller INTR output
Serial Port A
IRQ3 via SERIRQ
Serial Port B
IRQ4 via SERIRQ
Parallel Port / Generic IRQ5 via SERIRQ
Floppy Disk
IRQ6 via SERIRQ
Parallel Port / Generic IRQ7 via SERIRQ
Internal Real Time Clock Internal RTC
Generic
IRQ9 via SERIRQ
Generic
IRQ10 via SERIRQ
Generic
IRQ11 via SERIRQ
PS/2 Mouse
IRQ12 via SERIRQ
Internal
Primary IDE cable
State Machine output based on processor FERR#
assertion.
IRQ14 from input signal (primary IDE in legacy mode
only) or via SERIRQ
Secondary IDE Cable
IRQ15 from input signal (secondary IDE in legacy mode
only) or via SERIRQ
The ICH4 cascades the slave controller onto the master controller through master controller
interrupt input 2. This means there are only 15 possible interrupts for the ICH4 PIC.
Interrupts can individually be programmed to be edge or level, except for IRQ0, IRQ2, IRQ8#, and
IRQ13.
Note that previous PIIXn devices internally latched IRQ12 and IRQ1 and required a port 60h read
to clear the latch. The ICH4 can be programmed to latch IRQ12 or IRQ1 (see bit 11 and bit 12 in
General Control Register, D31:F0, offset D0h).
106
Intel^® 82801DB ICH4 Datasheet