P87LPC779FDH datasheet(27/74 Pages) PHILIPS

27 / 74 page

Philips Semiconductors

P87LPC779

CMOS single-chip 8-bit microcontroller

Product data

Rev. 02 — 03 May 2004

27 of 74

9397 750 13213

8.8 Interrupts

The P87LPC779 uses a four priority level interrupt structure. This allows great

ﬂexibility in controlling the handling of the P87LPC779’s many interrupt sources. The

P87LPC779 supports up to 13 interrupt sources.

Each interrupt source can be individually enabled or disabled by setting or clearing a

bit in registers IEN0 or IEN1. The IEN0 register also contains a global disable bit, EA,

which disables all interrupts at once.

Each interrupt source can be individually programmed to one of four priority levels by

setting or clearing bits in the IP0, IP0H, IP1, and IP1H registers. An interrupt service

routine in progress can be interrupted by a higher priority interrupt, but not by another

interrupt of the same or lower priority. The highest priority interrupt service cannot be

interrupted by any other interrupt source. So, if two requests of different priority levels

are received simultaneously, the request of higher priority level is serviced.

If requests of the same priority level are received simultaneously, an internal polling

sequence determines which request is serviced. This is called the arbitration ranking.

Note that the arbitration ranking is only used to resolve simultaneous requests of the

same priority level.

Table 19 summarizes the interrupt sources, ﬂag bits, vector addresses, enable bits,

priority bits, arbitration ranking, and whether each interrupt may wake up the CPU

from Power-down mode.

Table 18:

CT1, CT0 values

CT1, CT0

Min Time Count

(Machine Cycles)

CPU Clock Max

(for 100 kHz I2C-bus)

Timeout Period

(Machine Cycles)

1 0

8.4 MHz

1023

0 1

7.2 MHz

1022

0 0

6.0 MHz

1021

1 1

4.8 MHz

1020

Table 19:

Summary of interrupts

Description

Interrupt

Flag Bit(s)

Vector

Address

Interrupt

Enable Bit(s)

Interrupt

Priority

Arbitration

Ranking

Power-down

Wake-up

External Interrupt 0

IE0

0003h

EX0 (IEN0.0)

IP0H.0, IP0.0

1 (highest)

Yes

Timer0 Interrupt

TF0

000Bh

ET0 (IEN0.1)

IP0H.1, IP0.1

External Interrupt 1

IE1

0013h

EX1 (IEN0.2)

IP0H.2, IP0.2

Yes

Timer1 Interrupt

TF1

001Bh

ET1 (IEN0.3)

IP0H.3, IP0.3

Serial Port Tx and Rx

TI & RI

0023h

ES (IEN0.4)

IP0H.4, IP0.4

Brownout Detect

BOD

002Bh

EBO (IEN0.5)

IP0H.5, IP0.5

Yes

I2C-bus Interrupt

ATN

0033h

EI2 (IEN1.0)

IP1H.0, IP1.0

KBI Interrupt

KBF

003Bh

EKB (IEN1.1)

IP1H.1, IP1.1

Yes

Comparator 2 interrupt

CMF2

0043h

EC2 (IEN1.2)

IP1H.2, IP1.2

Yes

Watchdog Timer

WDOVF

0053h

EWD (IEN0.6)

IP0H.6, IP0.6

Yes

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