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AN2104
Using Background Debug Mode for the M68HC12 Family
Freescale Semiconductor, Inc...
By Timothy J. Airaudi
Applications Engineering, Microcontroller Division
Austin, Texas
Introduction
This application note describes the basic operation of the background
debug mode (BDM) and some of its applications, as it relates to
Motorola’s M68HC12 Family of microcontrollers (MCU). Examples of in-
circuit programming of internal FLASH memory and in-circuit debugging,
using P&E Microcomputer Systems’ BDM interface cable and its
software, are also contained in this document.
The BDM’s main purpose is to allow debugging of the actual
microcontroller being used in the user’s target application. This takes the
place of hardware such as an in-circuit emulator, which uses external
components to attempt to duplicate operation of the MCU from outside
of the target application.
Instead of having this external hardware, and a variety of potential
problems, the debug logic is built into the MCU’s on-chip integration
module. This differs from other systems that have the debugging logic
located in the central processor unit (CPU). Not having the debugging
logic in the CPU allows for reading and writing of memory locations,
while the CPU is executing user code, with no degradation in real-time
operation. This is an example of the BDM being enabled but not active.
© Freescale Semiconductor, Inc., 2004. All rights reserved.
© Motorola, Inc., 2001
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