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debugWIRE is a serial communications protocol, designed by Atmel. It is used for on-chip debugging of Atmel AVR microprocessors.


debugWIRE is designed as a simpler alternative to JTAG, aimed at processors with limited resources. It is supported by most modern 8-bit AVRs. By using debugWIRE one has full read and write access to all memory and full control over the execution flow. It supports single-step, run-to-cursor, step-out, and software break instructions. A breakpoint (run-to-cursor) will be set by reprogramming the BREAK[1] opcode into the FLASH storage of the AVR. Care must be taken due to the limited guaranteed write cycles (10000) of the device.[2]

Programmer models[edit]

debugWIRE is supported by all modern debuggers from Atmel. This includes the Atmel-ICE, the JTAGICE3, the AVR Dragon and the JTAGICE mkII.

debugWIRE specifications[edit]

debugWIRE is activated by setting (programming to zero) of the fuse DWEN (debugWIRE enable), normally located in the high fuse byte. After this action the /RESET pin function isn't available anymore and the ISP protocol cannot be used. debugWIRE can be disabled with e.g. JTAGICE mkII by sending a special reset command that disables temporarily the debugWIRE function and reenables /RESET and also ISP until next power down cycle. debugWIRE is not able to program the fuses of a device. If you want to disable debugWIRE permanently you have to disable the function temporarily and program the fuse using the now available ISP function.[3] debugWIRE uses a 1 wire open drain serial connection. The default baud rate used is AVR clock/128. Sending a BREAK 0x00 will return 0x55 which is used to detect the baud rate. The AVR will return a BREAK when a breakpoint is hit or a collision is detected on the debugWIRE connection. 0x06 is used to disable debugWIRE and reenable /RESET and ISP, 0x07 resets the AVR, 0xF0 returns the PC, 0xF3 the debugWIRE ID.[4][5][6]


  1. ^ AVR Assembler Instructions
  2. ^ ATtiny25-ATtiny45-ATtiny85_Datasheet-Summary.pdf
  3. ^ debugWIRE article (in German)
  4. ^ The debugWIRE protocol
  5. ^ Simple stand-alone debugWIRE debugger (open source)
  6. ^ Microchip Makes (25 November 2015). "Advanced Debugging with Arduino Boards" – via YouTube.