PIIX datasheet(102/122 Pages) INTEL

102 / 122 page

82371FB (PIIX) AND 82371SB (PIIX3)

102

Universal Serial

Bus D river (USBD)

Universal Host

Controller Driver (HCD)

PIIX3

Universal Host Controller (HC)

USB D evice

USB

usb_blk. drw

Hardware

Client Softw are

System

Software

USB Device

USB

Universal Host

Controller Interface

(UHCI)

USB_BLK

Figure 6. USB System Conceptual View

3.7.

Interval Timer

The PIIX/PIIX3 contains three counters that are equivalent to those found in the 82C54 programmable

interval timer. The three counters are contained in one PIIX/PIIX3 timer unit, referred to as Timer-1. Each

counter output provides a key system function. Counter 0 is connected to interrupt controller IRQ0 and

provides a system timer interrupt for a time-of-day, diskette time-out, or other system timing functions.

Counter 1 generates a refresh request signal and Counter 2 generates the tone for the speaker. The

14.31818 MHz counters normally use OSC as a clock source.

Counter 0, System Timer

This counter functions as the system timer by controlling the state of IRQ0 and is typically programmed for

mode 3 operation. The counter produces a square wave with a period equal to the product of the counter

period (838 ns) and the initial count value. The counter loads the initial count value one counter period after

software writes the count value to the counter I/O address. The counter initially asserts IRQ0 and decrements

the count value by two each counter period. The counter negates IRQ0 when the count value reaches 0. It

then reloads the initial count value and again decrements the initial count value by two each counter period.

The counter then asserts IRQ0 when the count value reaches 0, reloads the initial count value, and repeats

the cycle, alternately asserting and negating IRQ0.

PIIX Scheda tecnica(PDF) 102 Page - Intel Corporation