p89lpc904 NXP Semiconductors, p89lpc904 Datasheet - Page 20

• Manufacturer Part Number: p89lpc904
• Description: 8-bit Microcontrollers With Two-clock Accelerated 80c51 Core 1 Kb 3 V Byte-erasable Flash With 8-bit A/d Converter
• Manufacturer: NXP Semiconductors

Philips Semiconductors
9397 750 13521
Preliminary data
8.12.1 External interrupt inputs
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.
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
“Power reduction modes”
Rev. 02 — 25 June 2004
8-bit microcontrollers with two-clock accelerated 80C51 core
for details.
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
P89LPC904
Section 8.15
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