AT89C5131A View Datasheet(PDF) - Atmel Corporation

Part Name

Description

Manufacturer

AT89C5131A

USB Microcontrollers

Atmel Corporation 

AT89C5131A USB Bootloader

In-System

Programming

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

the USB bus without removing it from the system and without the need of a pre-programmed

application.

This section describes how to start the USB bootloader and the higher level protocol over the

USB.

Boot Process

The bootloader can be activated in two ways:

• Hardware conditions

• Regular boot process

Figure 3 and Figure 4 describe the boot process flows for low pin count and high pin count

products.

High Pin Count

Hardware Conditions

The Hardware conditions (EA = 1, PSEN = 0) during the RESET rising edge force the on-chip

bootloader execution. In this way the bootloader can be carried out regardless of the user Flash

memory content. It is recommended to pull the PSEN pin down to ground though a 1K resistor to

prevent the PSEN pin from being damaged (see Figure 2 below).

Figure 2. ISP Hardware conditions

VCC

VCC

VCC

EA

ALE

Unconnected

RST

XTAL2

Bootloader

/PSEN

XTAL1

C2

GND

Crystal

GND

C1

1K

GND GND

VSS

GND

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

code) after reset, it is recommended to release PSEN after rising edge of reset signal. The hard-

ware conditions are sampled at reset signal rising edge, thus they can be released at any time

when reset input is high.

Low Pin Count

Hardware Conditions

The Hardware Condition forces the bootloader execution from reset.

The default factory Hardware Condition is assigned to port P1.

• P1 must be equal to FEh

In order to offer the best flexibility, the user can define its own Hardware Condition on one of the

following Ports:

• Port1

5

4287E–USB–04/08

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