mc68hc11e0fnr2 Freescale Semiconductor, Inc, mc68hc11e0fnr2 Datasheet - Page 193

• Manufacturer Part Number: mc68hc11e0fnr2
• Description: Hc11 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Freescale Semiconductor
Application Note
M68HC11 Bootstrap Mode
By Jim Sibigtroth
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:
© Freescale Semiconductor, Inc., 2005. All rights reserved.
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Mike Rhoades
John Langan
Austin, Texas
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
Rev. 1.1, 07/2005
AN1060