Debug wire is an interface which enables debugging AVR microcontrollers by using one wire. All new AVR microcontrollers with less than 16kByte memory have built in one wire bidirectional debugging interface which allows debugging devices at the real time.

Like JTAG interface DebugWIRE can handle full execution and program flow control. It also supports unlimited number of breakpoints, adjusting memory contents. Good thing is that interface doesn’t require additional pins as only RESET pin is used for debugging purposes.

To enable debugwire interface DWEN fuse has to be programmed also lock bits has to be un-programmed. Then RESET port pin is activated as open-drain bi directional I/O pin with pullup enabled. Reset pin becomes communication gateway between target and emulator. When debugging external reset circuitry should be disconnected – so no external reset source will be present during debugging.

Debug wire adapter-debugger communicates through one data register DWDR which can only be accessed by debugger.

Using debugwire there it isnot possible to program Fuse settings, so it has to be done via ISP as debugWire is only for debugging and not for programming like JTAG. So once debugwire is enabled ISP becomes disables as RESET pin purpose is changed. So you need to restore from dw withing debugging system to be able to program chip again. Debugwire interface can be accessed using AVRStudio and AVRJTAG MKII adapter. With AVRStudio and AVRJTAG MKII you dont have bother about entering DW and exiting from debugging as it is done automatically.

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This entry was posted on Tuesday, June 5th, 2007 at 11:34 am and is filed under AVR Microcontrollers. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.