6.2.5 debugWIRE

The debugWIRE interface was developed by Atmel for use on low pin-count devices. Unlike the JTAG interface which uses four pins, debugWIRE makes use of just a single pin (RESET) for bi-directional half-duplex asynchronous communication with the debugger tool.

When designing an application PCB, which includes an Atmel AVR with the debugWIRE interface, the pinout shown in Figure 6-7 should be used.

Figure 6-7. debugWIRE (SPI) Header Pinout

Note: The debugWIRE interface can not be used as a programming interface. This means that the SPI interface must also be available (as shown in Figure 6-8) in order to program the target.

When the debugWIRE enable (DWEN) fuse is programmed and lock-bits are un-programmed, the debugWIRE system within the target device is activated. The RESET 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 debugger.