MC68HC705MC4MP datasheet(40/180 Pages) FREESCALE

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Interrupts

MC68HC705MC4 — Rev. 2.0

Interrupts

Interrupts cause the processor to save the register contents on the stack

and to set the interrupt mask (I-bit) to prevent additional interrupts.

Unlike RESET, hardware interrupts do not cause the current instruction

execution to be halted, but are considered pending until the current

instruction is completed.

When the current instruction is completed, the processor checks all

pending hardware interrupts. If interrupts are not masked (I-bit in the

condition code register is clear), and the corresponding interrupt enable

bit is set, the processor proceeds with interrupt processing. Otherwise,

the next instruction is fetched and executed. The SWI is executed the

same as any other instruction, regardless of the I-bit state.

When an interrupt is to be processed, the CPU puts the register contents

on the stack, sets the I-bit in the CCR, and fetches the address of the

corresponding interrupt service routine from the vector table at locations

$0FF0 through $0FFF. If more than one interrupt is pending when the

interrupt vector is fetched, the interrupt with the highest vector location

shown in Table 4-1 will be serviced first.

An RTI instruction is used to signify when the interrupt software service

routine is completed. The RTI instruction causes the CPU state to be

recovered from the stack and normal processing to resume at the next

Table 4-1. Vector Addresses for Interrupts and Reset

Flag

Name

Interrupts

CPU

Interrupt

Vector

Address

N/A

Reset

RESET

$0FFE–$0FFF

N/A

Software

SWI

$0FFC–$0FFD

ISCR

REQ

External Interrupt

IRQ

$0FFA–$0FFB

TSR

ICF2

Timer Input Capture 2

TIMER

$0FF8–$0FF9

TSR

ICF1

Timer Input Capture 1

TIMER

$0FF6–$0FF7

TSR

OCF

Timer Output Compare*

TIMER

$0FF4–$0FF5

TSR

TOF

Timer Overﬂow*

TIMER

$0FF4–$0FF5

SCSR

Various

SCI

$0FF2–$0FF3

CTCSR

CTOF

Core Timer Overﬂow*

CTIMER

$0FF0–$0FF1

CTCSR

RTIF

Core Timer Real Time*

CTIMER

$0FF0–$0FF1

* Vector is shared

Freescale Semiconductor, Inc.

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