82374EB datasheet(153/208 Pages) INTEL

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82374EB82374SB

Table 24 Typical Interrupt Functions

Priority

Label

Controller

Typical Interrupt Source

IRQ0

Interval Timer 1 Counter 0 OUT

IRQ1

Keyboard

3-10

IRQ2

Interrupt from Controller 2

IRQ8

Real Time Clock

IRQ9

Expansion Bus Pin B04

IRQ10

Expansion Bus Pin D03

IRQ11

Expansion Bus Pin D04

IRQ12

Expansion Bus Pin D05

IRQ13

Coprocessor Error Chaining

IRQ14

Fixed Disk Drive Controller Expansion Bus Pin D07

IRQ15

Expansion Bus Pin D06

IRQ3

Serial Port 2 Expansion Bus B25

IRQ4

Serial Port 1 Expansion Bus B24

IRQ5

Parallel Port 2 Expansion Bus B23

IRQ6

Diskette Controller Expansion Bus B22

IRQ7

Parallel Port 1 Expansion Bus B21

91 Interrupt Controller Internal Registers

Several registers are contained internally within each 82C59 The interrupts at the IRQ input lines are handled

by two registers in cascade the Interrupt Request Register (IRR) and the In-Service Register (ISR) The IRR is

used to store all the interrupt levels which are requesting service and the ISR is used to store all the interrupt

levels which are being serviced

Internal circuitry determines the priorities of the bits set in the IRR The highest priority is selected and strobed

into the corresponding bit of the ISR during Interrupt Acknowledge Cycles

The Interrupt Mask Register (IMR) stores the bits which mask the incoming interrupt lines The IMR operates

on the IRR Masking of a higher priority input will not effect the interrupt request lines of lower priority inputs

92 Interrupt Sequence

The powerful features of the Interrupt Controller in a microcomputer system are its programmability and the

interrupt routine addressing capability The latter allows direct or indirect jumping to the specific interrupt

routine requested without any polling of the interrupting devices The following shows the interrupt sequence

for an x86 type system (the 8080 mode of the interrupt controller must never be selected when programming

the ESC)

153

82374EB Datasheet(PDF) 153 Page - Intel Corporation

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