MC68HC11E0CFNE3 Datasheet, PDF (193/242 Pages) Freescale Semiconductor, Inc – M68HC11E Family

Freescale Semiconductor
Application Note
AN1060
Rev. 1.1, 07/2005
M68HC11 Bootstrap Mode
By Jim Sibigtroth
Mike Rhoades
John Langan
Austin, Texas
Introduction
The M68HC11 Family of MCUs (microcontroller units) has a bootstrap mode that allows a user-defined
program to be loaded into the internal random-access memory (RAM) by way of the serial
communications interface (SCI); the M68HC11 then executes this loaded program. The loaded program
can do anything a normal user program can do as well as anything a factory test program can do because
protected control bits are accessible in bootstrap mode. Although the bootstrap mode is a single-chip
mode of operation, expanded mode resources are accessible because the mode control bits can be
changed while operating in the bootstrap mode.
This application note explains the operation and application of the M68HC11 bootstrap mode. Although
basic concepts associated with this mode are quite simple, the more subtle implications of these functions
require careful consideration. Useful applications of this mode are overlooked due to an incomplete
understanding of bootstrap mode. Also, common problems associated with bootstrap mode could be
avoided by a more complete understanding of its operation and implications.
Topics discussed in this application note include:
• Basic operation of the M68HC11 bootstrap mode
• General discussion of bootstrap mode uses
• Detailed explanation of on-chip bootstrap logic
• Detailed explanation of bootstrap firmware
• Bootstrap firmware vs. EEPROM security
• Incorporating the bootstrap mode into a system
• Driving bootstrap mode from another M68HC11
• Driving bootstrap mode from a personal computer
• Common bootstrap mode problems
• Variations for specific versions of M68HC11
• Commented listings for selected M68HC11 bootstrap ROMs
© Freescale Semiconductor, Inc., 2005. All rights reserved.