AT89C51ID2-RDTIM datasheet(124/159 Pages) ATMEL

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124

AT89C51ID2

4289A–8051–09/03

Bootloader Functionality

Introduction

The bootloader can be activated by two means: Hardware conditions or regular boot

process.

The Hardware conditions (EA = 1, PSEN = 0) during the Reset# falling edge force the

on-chip bootloader execution. This allows an application to be built that will normally

execute the end user’s code but can be manually forced into default ISP operation.

As PSEN is a an output port in normal operating mode after reset, user application

should take care to release PSEN after falling edge of reset signal. The hardware condi-

tions are sampled at reset signal falling edge, thus they can be released at any time

when reset input is low.

The on-chip bootloader boot process is shown Figure 49

Purpose

Hardware Conditions

The Hardware Conditions force the bootloader execution whatever BLJB,

BSB and SBV values.

BLJB

The Boot Loader Jump Bit forces the application execution.

BLJB = 0 => Boot loader execution.

BLJB = 1 => Application execution

The BLJB is a fuse bit in the Hardware Byte.

That can be modified by hardware (programmer) or by software (API).

Note:

The BLJB test is perform by hardware to prevent any program

execution..

SBV

The Software Boot Vector contains the high address of custumer

bootloader stored in the application.

SBV = FCh (default value) if no custumer bootloader in user Flash.

Note:

The costumer bootloader is called by JMP [SBV]00h instruction.

AT89C51ID2-RDTIM 데이터시트(PDF) 124 Page - ATMEL Corporation