© 2008 Microchip Technology Inc. DS01157A-page 1
AN1157
INTRODUCTION
One of the advantages of Microchip’s PIC
®
micro-
controllers with self-programmable enhanced Flash
memory is the ability to implement a bootloader. This
allows designers to implement applications that can be
updated many times over, potentially extending the
application’s useful lifetime.
This application note describes a serial bootloader for
16-bit PIC24F devices using the UART module as a
communication channel. The bootloader application
uses the communication protocols originally outlined in
Microchip Application Note AN851, “A Flash Bootloader
for PIC16 and PIC18 Devices”. Some modifications to
the original protocol have been made to maintain
compatibility with the PIC24 architecture. It has also
been redesigned to accommodate the current genera-
tion of PIC24FJ Flash microcontrollers, as well as the
next generation of PIC24F devices.
FIRMWARE
Basic Operation
Figure 1 summarizes the essential firmware design of
the bootloader. Data is received through the UART
module and passed through the transmit/receive
engine. The engine filters and parses the data, storing
the information into a data buffer in RAM. The com-
mand interpreter evaluates the command information
within the buffer to determine what should be done
(e.g., Is the data written into memory? Is data read from
memory? Does the firmware version need to be read?).
Once the operation is performed, reply data is passed
back to the transmit/receive engine to be transmitted
back to the source, closing the software flow control
loop.
FIGURE 1: BOOTLOADER FUNCTIONAL
BLOCK DIAGRAM
COMMUNICATIONS
The microcontroller’s UART module is used to receive
and transmit data; it is configured to be compatible with
RS-232 communications. The device can be set up in
an application to bootload from a computer through its
standard serial interface. The following default
communication settings are used:
• 8 Data Bits
•No Parity
• 1 Stop Bit
• Automatic Baud Rate Detection
The baud rate is detected using the UART module’s
hardware auto-baud functionality. For more information
on this feature, refer to the UART chapter of the
“PIC24F Family Reference Manual” (Section 21.
“UART” (DS39708)).
Author: Brant Ivey
Microchip Technology Inc.
UART
Transmit/Receive
Engine
RAM
Buffer
Command
Interpreter
Flash
Program
Memory
EE
Configuration
Data
Memory*
UxTXUxRX
Registers*
Bootloader
Control
Firmware
Data Bus
* If present on target device. See text for details.
A Serial Bootloader for PIC24F Devices
