P89LPC901FD datasheet(40/55 Pages) PHILIPS

40 / 55 page

Philips Semiconductors

P89LPC901/902/903

8-bit microcontrollers with two-clock 80C51 core

Product data

Rev. 04 — 21 November 2003

40 of 55

9397 750 12293

8.25 Additional features

8.25.1

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.

8.25.2

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 register.

8.26 Flash program memory

8.26.1

General description

The P89LPC901/902/903 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

Chip Erase operation will erase the entire program memory. In-Circuit Programming

using standard commercial programmers is available. In addition, In-Application

Programming (IAP) and byte erase allows code memory to be used for non-volatile

data storage. On-chip erase and write timing generation contribute to a user-friendly

programming interface. The P89LPC901/902/903 Flash reliably stores memory

contents even after more than 100,000 erase and program cycles. The cell is

(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 20. 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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