P87LPC768FD datasheet(27/64 Pages) PHILIPS

27 / 64 page

Philips Semiconductors

Preliminary data

87LPC768

Low power, low price, low pin count (20 pin) microcontroller

with 4 kB OTP 8-bit A/D, Pulse Width Modulator

2001 Aug 06

External Interrupt Inputs

The 87LPC768 has two individual interrupt inputs as well as the

Keyboard Interrupt function. The latter is described separately

elsewhere in this section. The two interrupt inputs are identical to

those present on the standard 80C51 microcontroller.

The external sources can be programmed to be level-activated or

transition-activated by setting or clearing bit IT1 or IT0 in Register

TCON. If ITn = 0, external interrupt n is triggered by a detected low

at the INTn pin. If ITn = 1, external interrupt n is edge triggered. In

this mode if successive samples of the INTn pin show a high in one

cycle and a low in the next cycle, interrupt request flag IEn in TCON

is set, causing an interrupt request.

Since the external interrupt pins are sampled once each machine

cycle, an input high or low should hold for at least 6 CPU Clocks to

ensure proper sampling. If the external interrupt is

transition-activated, the external source has to hold the request pin

high for at least one machine cycle, and then hold it low for at least

one machine cycle. This is to ensure that the transition is seen and

that interrupt request flag IEn is set. IEn is automatically cleared by

the CPU when the service routine is called.

If the external interrupt is level-activated, the external source must

hold the request active until the requested interrupt is actually

generated. If the external interrupt is still asserted when the interrupt

service routine is completed another interrupt will be generated. It is

not necessary to clear the interrupt flag IEn when the interrupt is

level sensitive, it simply tracks the input pin level.

If an external interrupt is enabled when the 87LPC768 is put into

Power Down or Idle mode, the interrupt will cause the processor to

wake up and resume operation. Refer to the section on Power

Reduction Modes for details.

SU01353

WAKEUP

(IF IN POWER

DOWN)

(FROM IEN0

INTERRUPT

TO CPU

IE0

EX0

IE1

EX1

BOD

EBO

KBF

EKB

CM2

EC2

WDT

EWD

ADC

EAD

TF0

ET0

TF1

ET1

RI + TI

ATN

EI2

CM1

EC1

Figure 12. Interrupt Sources, Interrupt Enables, and Power Down Wakeup Sources

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