P89LPC915FDH datasheet(53/72 Pages) PHILIPS

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Philips Semiconductors

P89LPC915/916/917

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

Product data

Rev. 04 — 17 December 2004

53 of 72

9397 750 14397

can only be reset by a power-on reset. When the Watchdog feature is disabled, it can

be used as an interval timer and may generate an interrupt. Figure 21 shows the

Watchdog timer in Watchdog mode. Feeding the Watchdog requires a two-byte

sequence. If PCLK is selected as the Watchdog clock and the CPU is powered-down,

the Watchdog is disabled. The Watchdog timer has a time-out period that ranges

from a few

µs to a few seconds. Please refer to the P89LPC915/916/917 User’s

Manual for more details.

9.27 Additional features

9.27.1

Software reset

The SRST bit in AUXR1 gives software the opportunity to reset the processor

completely, as if an external reset or Watchdog reset had occurred. Care should be

taken when writing to AUXR1 to avoid accidental software resets.

9.27.2

Dual data pointers

The dual Data Pointers (DPTR) provides two different Data Pointers to specify the

address used with certain instructions. The DPS bit in the AUXR1 register selects

one of the two Data Pointers. Bit 2 of AUXR1 is permanently wired as a logic 0 so that

the DPS bit may be toggled (thereby switching Data Pointers) simply by incrementing

the AUXR1 register, without the possibility of inadvertently altering other bits in the

9.28 Flash program memory

9.28.1

General description

The P89LPC915/916/917 Flash memory provides in-circuit electrical erasure and

programming. The Flash can be erased, read, and written as bytes. The Sector and

Page Erase functions can erase any Flash sector (256 bytes) or page (16 bytes). The

(1) Watchdog reset can also be caused by an invalid feed sequence, or by writing to WDCON not immediately followed by a

feed sequence.

Fig 21. Watchdog timer in Watchdog mode (WDTE = 1).

PRE2

PRE1

PRE0

–

WDRUN

WDTOF

WDCLK

WDCON (A7H)

CONTROL REGISTER

PRESCALER

002aaa423

SHADOW

FOR WDCON

8-BIT DOWN

COUNTER

WDL (C1H)

Watchdog

oscillator

PCLK

÷32

MOV WFEED1, #0A5H

MOV WFEED2, #05AH

RESET

see note (1)

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