The debugWIRE communication pin (dW) is physically located on the same pin as the external reset (/RESET). An external reset source is therefore not supported when the debugWIRE interface is enabled.

The debugWIRE Enable fuse (DWEN) must be set on the target device in order for the debugWIRE interface to function. This fuse is by default un-programmed when the Atmel AVR device is shipped from the factory. The debugWIRE interface itself cannot be used to set this fuse. In order to set the DWEN fuse, SPI mode must be used. The software front-end handles this automatically provided that the necessary SPI pins are connected. It can also be set using SPI programming from the Atmel Studio programming dialog.

To disable the debugWIRE interface, use high-voltage programming to un-program the DWEN fuse. Alternately, use the debugWIRE interface itself to temporarily disable itself, which will allow SPI programming to take place, provided that the SPIEN fuse is set.

Note: If the SPIEN fuse was NOT left programmed, Atmel Studio will not be able to complete this operation, and high-voltage programming must be used.

Having the DWEN fuse programmed enables some parts of the clock system to be running in all sleep modes. This will increase the power consumption of the AVR while in sleep modes. The DWEN Fuse should therefore always be disabled when debugWIRE is not used.

When designing a target application PCB where debugWIRE will be used, the following considerations must be made for correct operation:

Never program the lock-bits on the target device. The debugWIRE interface requires that lock-bits are cleared in order to function correctly.