By following the description below, the SPI Interface is re-enabled.
Connect the Atmel AVR Dragon to the target with SPI (6-pin connection) as described above.
Load a project and Start a debug session using the "Start Debugging" command (found under the Debug pull-down menu in Atmel Studio).
In the debug menu, you should now be able to choose "Disable debugWIRE and close ".
Some precautions regarding the RESET line must be taken to ensure proper communication over the debugWIRE interface. If there is a pull-up on the RESET line, this resistor must be larger than 10kΩ, and there should be no capacitive load. The pull-up resistor is not required for debugWIRE functionality. Other logic connected to the RESET line should be removed.
It's not possible to use the debugWIRE interface if the lockbits on the target AVR are programmed. Always be sure that the lockbits are cleared before programming the DWEN fuse and never set the lockbits while the DWEN fuse is programmed. If both the debugWIRE enable fuse (DWEN) and lockbits are set, one can use High Voltage Programming to do a chip erase, hence clear the lockbits. When the lockbits are cleared the debugWIRE interface will be re-enabled.
The SPI Interface is only capable of reading fuses, signature, and do a chip erase when the DWEN fuse is unprogrammed.