Physical Interface

When the debugWIRE Enable (DWEN) bit is programmed to '0' and Lock bits are unprogrammed ('1'), the debugWIRE system within the target device is activated. The RESET port pin is configured as a wire-AND (open-drain) bi-directional I/O pin with pull-up enabled and becomes the communication gateway between target and emulator.

Figure 1. The debugWIRE Setup

The debugWIRE Setup shows the schematic of a target MCU, with debugWIRE enabled, and the emulator connector. The system clock is not affected by debugWIRE and will always be the clock source selected by the CKSEL Fuses.

When designing a system where debugWIRE will be used, the following observations must be made for correct operation: