Background debug mode interface

Background debug mode (BDM) interface is an electronic interface that allows debugging of embedded systems. Specifically, it provides in-circuit debugging functionality in microcontrollers. It requires a single wire and specialized electronics in the system being debugged. It appears in many Freescale Semiconductor products. Background commands are categorized into two types: Non-intrusive commands and Active background commands. Non-intrusive commands can be issued while the user program is running, which include memory access commands.

The interface allows a Host to manage and query a target. Specialized hardware is required in the target device. No special hardware is required in the host; a simple bidirectional I/O pin is sufficient.