Philips Semiconductors
P89LPC920/921/922/9221
8-bit microcontrollers with two-clock 80C51 core
Product data Rev. 08 — 15 December 2004 18 of 46
9397 750 14469
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
8.10 Data RAM arrangement
The 256 bytes of on-chip RAM are organized as shown in Table 5.
8.11 Interrupts
The P89LPC920/921/922/9221 uses a four priority level interrupt structure. This
allows great flexibility in controlling the handling of the many interrupt sources. The
P89LPC920/921/922/9221 supports 12 interrupt sources: external interrupts 0 and 1,
timers 0 and 1, serial port Tx, serial port Rx, combined serial port Rx/Tx, brownout
detect, watchdog/real-time clock, I
2
C, keyboard, and comparators 1 and 2.
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.
8.11.1 External interrupt inputs
The P89LPC920/921/922/9221 has two external interrupt inputs as well as the
Keypad Interrupt function. The two interrupt inputs are identical to those present on
the standard 80C51 microcontrollers.
These external interrupts can be programmed to be level-triggered or edge-triggered
by setting or clearing bit IT1 or IT0 in Register TCON.
In edge-triggered mode if successive samples of the INTn pin show a HIGH in one
cycle and a LOW in the next cycle, the interrupt request flag IEn in TCON is set,
causing an interrupt request.
If an external interrupt is enabled when the P89LPC920/921/922/9221 is put into
Power-down or Idle mode, the interrupt will cause the processor to wake-up and
resume operation. Refer to Section 8.14 “Power reduction modes” for details.
Table 5: On-chip data memory usages
Type Data RAM Size (bytes)
DATA Memory that can be addressed directly and indirectly 128
IDATA Memory that can be addressed indirectly 256
