AT89C5132-ROTIL datasheet(34/181 Pages) ATMEL

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4173D–USB–02/06

AT89C5132

10. Interrupt System

The AT89C5132, like other control-oriented computer architectures, employ a program interrupt

method. This operation branches to a subroutine and performs some service in response to the

interrupt. When the subroutine terminates, execution resumes at the point where the interrupt

occurred. Interrupts may occur as a result of internal AT89C5132 activity (e.g., timer overflow) or

at the initiation of electrical signals external to the microcontroller (e.g., keyboard). In all cases,

interrupt operation is programmed by the system designer, who determines priority of interrupt

service relative to normal code execution and other interrupt service routines. All of the interrupt

sources are enabled or disabled by the system designer and may be manipulated dynamically.

A typical interrupt event chain occurs as follows:

An internal or external device initiates an interrupt-request signal. The AT89C5132, latch

this event into a flag buffer.

The priority of the flag is compared to the priority of other interrupts by the interrupt han-

dler. A high priority causes the handler to set an interrupt flag.

This signals the instruction execution unit to execute a context switch. This context

switch breaks the current flow of instruction sequences. The execution unit completes

the current instruction prior to a save of the program counter (PC) and reloads the PC

with the start address of a software service routine.

The software service routine executes assigned tasks and as a final activity performs a

RETI (return from interrupt) instruction. This instruction signals completion of the inter-

rupt, resets the interrupt-in-progress priority and reloads the program counter. Program

operation then continues from the original point of interruption.

Table 32. Interrupt System Signals

Six interrupt registers are used to control the interrupt system. Two 8-bit registers are used to

enable separately the interrupt sources: IEN0 and IEN1 registers (see Table 35 and Table 36).

Four 8-bit registers are used to establish the priority level of the sources: IPH0, IPL0, IPH1 and

IPL1 registers (see Table 10-1 to Table 39).

10.1

Interrupt System Priorities

Each of the interrupt sources on the AT89C5132 can be individually programmed to one of four

priority levels. This is accomplished by one bit in the Interrupt Priority High registers (IPH0 and

IPH1) and one bit in the Interrupt Priority Low registers (IPL0 and IPL1). This provides each

interrupt source four possible priority levels according to Table 33.

Signal

Name

Type

Description

Alternate

Function

INT0

External Interrupt 0

See Section "External Interrupts", page 37.

P3.2

INT1

External Interrupt 1

See Section “External Interrupts”, page 37.

P3.3

KIN3:0

Keyboard Interrupt Inputs

See Section “Keyboard Interface”, page 152.

P1.3:0

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