AN2295 Freescale Semiconductor / Motorola, AN2295 Datasheet - Page 2

• Manufacturer Part Number: AN2295
• Description: Developers Serial Bootloader for M68HC08 and HCS08 MCUs
• Manufacturer: Freescale Semiconductor / Motorola

Project Objectives
Project Goals
Freescale Semiconductor M68HC08 MCUs use a standard monitor mode interface for FLASH
programming. Configuration of monitor mode requires a specific clock and high voltage (monitor mode
entry voltage V
mode communication uses a few pins. If the application already uses a standard serial SCI interface for
communication, a different code (the bootloader) can be used to communicate with the PC using the
same interface that is used for reprogramming.
The bootloader can be used only for reprogramming, not for in-circuit debugging. The bootloader is a
low-cost, in-circuit programming solution.
Requirements
This bootloader application requires:
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Low memory use — The bootloader must use as little memory as possible. Other versions of
bootloaders use more than 1 KB of memory, which is unacceptable on devices with 3 KB of
memory available (such as the MC68HC908JK3). The solution described in this document
implements all features as simply as possible, excluding checksums, etc. The target size is less
than 500 B.
Low pin-count — This bootloader uses standard (already implemented) means of communication
(typically SCI on boards that are primarily intended for communication). The standard SCI uses two
wires (RxD, TxD). No additional wires are used to start bootloader.
Transparency with respect to the user S19 file — The complete application should be
transparent to the user code S19 file. This means that no adjustments are required in the S19 file.
Other M68HC08 and HCS08 bootloader applications require modification to interrupt vectors or
other modifications to the S19 file for it to accept the bootloader.
(under development or re-configuration)
HC(S)08 Embedded Application
tst
= V
DD
Developer’s Serial Bootloader for M68HC08 and HCS08 MCUs, Rev. 6
+ 2.5 = 8 V) applied to the IRQ pin upon MCU startup. Also, establishing monitor
Figure 1. Top Level View
Windows or Linux PC
Freescale Semiconductor