T89C51RD2-RDTIM datasheet(61/104 Pages) ATMEL

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T89C51RD2

4243G–8051–05/03

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 an output port in normal operating mode (running user application or boor-

loader code) after reset, it is recommended to release PSEN after falling edge of reset

signal. The hardware conditions 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 in Figure 24.

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 custumer bootloader is called by LJMP [SBV]00h instruction.

T89C51RD2-RDTIM 数据表(PDF) 61 Page - ATMEL Corporation