Specifications

Developer’s Serial Bootloader, Rev. 13
Project objectives
Freescale Semiconductor2
modifications to be done in-circuit. The serial bootloader offers a zero-cost solution to applications already
equipped with a serial interface and SCI pins available on a connector. This document also describes other
programming techniques:
• FLASH reprogramming using ROM routines
• Simple software SCI
• Software for USB (HC08JW, HCS08JM and MCF51JM MCUs)
• Use of the internal clock generator
• PLL clock programming
• EEPROM programming (AS/AZ HC08 families)
• CRC protection of serial protocol option
Figure 1. Top-level view
1.1 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
TST
= V
DD
+ 2.5 = 8 V) applied to the IRQ pin upon MCU startup. Also, establishing
monitor-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 used for reprogramming.
The bootloader can be used for only reprogramming, not for in-circuit debugging. The bootloader is a
low-cost in-circuit programming solution.
1.2 Bootloader application requirements
The following points described important parameters of the bootloader application:
• 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