AT89C51AC2(2005) データシートの表示（PDF） - Atmel Corporation

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AT89C51AC2
(Rev.:2005)

80C51 Microcontrollers

Atmel Corporation 

In-System

Programming

Boot Process

Hardware Condition

The ISP allows the user to program or reprogram a microcontroller’s on-chip Flash

memory through the serial line without removing it from the system and without the need

of a pre-programmed application.

This section describes how to start the UART bootloader and the higher level protocols

over the serial line.

The bootloader can be activated in two ways:

• Hardware condition

• Regular boot process

The Hardware Conditions (EA = 1, PSEN = 0) during the RESET falling edge force the

on-chip bootloader execution. In this way the bootloader can be carried out whatever the

user Flash memory content.

As PSEN is an output port in normal operating mode (running user application or boot-

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.

6 A/T89C51AC2 UART Bootloader

4231C–CAN–03/05

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