BDM (background debugging mode) of Motorola 68HC12 processors is

• special CPU mode, in which is possible to intervene in a program execution, to read and write memory and registers, debug the program (set breakpoints, watchpoints, step)
• interface of HC12 CPU, which is used to control BDM mode (from another computer)

The BDM interface is used either for HC12 microcontroller program debugging as for programming of their FLASH memories. BDM is the most convenient way to program internal FLASH memory of HC12, but it is also able to program external memories, which are found eg. on some development boards.

BDM podex Scheme:

BDM podex firmware source :

BDM podex firmware:

BDM software for read/write EEPROM , FLASH: