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 incircuit 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.