 2009 Microchip Technology Inc.

DS01302A-page 1

AN1302

INTRODUCTION

The new PIC16F1XXX enhanced core microcontroller

has the ability to write its own program memory under

software control. This allows the microcontroller to

make modifications in the program Flash memory. This

application note explains the implementation of a

BOOTLOADER CONCEPT

The bootloader allows a processor to change its

firmware without any physical intervention to the device

itself. There is no need for a hardware programmer

when

using

the

bootloader.

The

firmware

is

downloaded from a host system by means of a

communication channel, usually through a USB or a

serial port. This bootloader implementation uses a

the microcontroller and the host system.

In general, when using a bootloader, the code is

transferred from a host device. Typically, this is

comprised of a PC computer using a RS-232 serial

cable or a USB port. Any other device can act as a host

device.

The target device needs bootloader firmware. This is

basically a software that accepts commands and data

from a host device and reads/erases/writes data to the

Flash program memory. This firmware is typically

located on the lower part of the program memory. The

bootloader code is started by default at system Reset.

It then checks if there is any application code loaded

and jumps into application code if any is found.

Alternatively, a button can be used to instruct the

bootloader to stay in bootloader code even if a firmware

is already present. This is useful when reading the

application firmware or in case of an application

firmware update.

BOOTLOADER REQUIREMENTS

The bootloader makes it unnecessary for any physical

intervention with a hardware programmer. The target

device must have some form of data connection with

with other devices on the bus, then no additional

connection is needed.

The bootloader will require the lower side of the

program memory reserved for the bootloader firmware

(see Figure 1). The rest of the program memory can be

used by application. No RAM memory needs to be

reserved, since it is used in different contexts and not

at the same time.

FIGURE 1:

FLASH MEMORY MAP

Author:

Cristian Toma

Microchip Technology Inc.