P89LPC904FD datasheet(20/41 Pages) PHILIPS

20 / 41 page

Philips Semiconductors

P89LPC904

8-bit microcontrollers with two-clock accelerated 80C51 core

Preliminary data

Rev. 02 — 25 June 2004

20 of 41

9397 750 13521

8.12 Interrupts

The P89LPC904 supports 10 interrupt sources: timers 0 and 1, serial port Tx, serial

port Rx, combined serial port Rx/Tx, brownout detect, Watchdog/real-time clock,

keyboard, and comparators 1 and 2, and the A/D converter.

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

bit in the interrupt enable registers IEN0 or IEN1. The IEN0 register also contains a

global disable bit, EA, which disables all interrupts.

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

setting or clearing bits in the interrupt priority registers IP0, IP0H, IP1, and IP1H. 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. If two requests of

different priority levels are pending at the start of an instruction, the request of higher

priority level is serviced.

If requests of the same priority level are pending at the start of an instruction, 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 pending

requests of the same priority level.

8.12.1

External interrupt inputs

The P89LPC904 has a Keypad Interrupt function. This can be used as an external

interrupt input.

If enabled when the P89LPC904 is put into Power-down or Idle mode, the interrupt

will cause the processor to wake-up and resume operation. Refer to Section 8.15

“Power reduction modes” for details.

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