PIIX datasheet(103/122 Pages) INTEL

103 / 122 page

82371FB (PIIX) AND 82371SB (PIIX3)

103

Counter 1, Refresh Request Signal

This counter provides the refresh request signal and is typically programmed for mode 2 operation. The

counter negates refresh request for one counter period (838 ns) during each count cycle. The initial count

value is loaded one counter period after being written to the counter I/O address. The counter initially asserts

refresh request, and negates it for 1 counter period when the count value reaches 1. The counter then

asserts refresh request and continues counting from the initial count value.

Counter 2, Speaker Tone

This counter provides the speaker tone and is typically programmed for mode 3 operation. The counter

provides a speaker frequency equal to the counter clock frequency (1.193 MHz) divided by the initial count

value. The speaker must be enabled by a write to port 061h.

3.8.

Interrupt Controller

The PIIX/PIIX3 provides an ISA compatible interrupt controller that incorporates the functionality of two

82C59 interrupt controllers. The two controllers are cascaded so that 13 external and three internal interrupts

are possible. The master interrupt controller provides IRQ [7:0] and the slave interrupt controller provides IRQ

[15:8] (Figure 7). The three internal interrupts are used for internal functions only and are not available to the

user. IRQ2 is used to cascade the two controllers together. IRQ0 is used as a system timer interrupt and is

tied to Interval Timer 1, Counter 0. The MIRQ0/IRQ0 pin will function as the IRQ0 output and should be

connected to the INTIN2 input of the IOAPIC when IRQ0 enable bit is set in the MIRQ0 register. IRQ13 is

connected internally to FERR#. The remaining 13 interrupt lines (IRQ[15,14,12:3,1]) are available for external

system interrupts. Edge or level sense selection is programmable on an individual channel by channel basis.

The Interrupt unit also supports interrupt steering. The PIIX/PIIX3 can be programmed to allow the four PCI

active low interrupts (PIRQ[D:A]#) to be internally routed to one of 11 interrupts (IRQ[15,14,12:9,7:3]). In

addition, the motherboard interrupts (MIRQ[1:0] for PIIX and MIRQ0 for PIIX3) may be routed to any of the 11

interrupts.

The Interrupt Controller consists of two separate 82C59 cores. Interrupt Controller 1 (CNTRL-1) and Interrupt

Controller 2 (CNTRL-2) are initialized separately and can be programmed to operate in different modes. The

default settings are: 80x86 Mode, Edge Sensitive (IRQ[15:0]) Detection, Normal EOI, Non-Buffered Mode,

Special Fully Nested Mode disabled, and Cascade Mode. CNTRL-1 is connected as the Master Interrupt

Controller and CNTRL-2 is connected as the Slave Interrupt Controller.

Note that IRQ13 is generated internally (as part of the coprocessor error support) by the PIIX. IRQ12/M is

generated internally (as part of the mouse support) when bit-4 in the XBCS Register is set to a 1. When this

bit is set to a 0, the standard IRQ12 function is provided and IRQ12 appears externally.

INTR

(To CPU)

82C59

Core

Controller 1

(Master)

Timer 1

Counter 0

IRQ1

IRQ3

IRQ4

IRQ5

IRQ6

IRQ7

051904_3.drw

82C59

Core

Controller 2

(Slave)

IRQ9

IRQ11

IRQ12/Mouse

FERR#

IRQ14

IRQ15

INTR

IRQ8#

IRQ10

051904

Figure 7. Block Diagram of the Interrupt Controller

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