Editing AVR microcontrollers (section)

== Debugging interfaces ==
<!--NOTE: This section was originally started by copying part of http://en.wikibooks.org/wiki/Embedded_Systems/Atmel_AVR#Debugging_Interfaces on February 20, 2011 -->
The AVR offers several options for debugging, mostly involving on-chip debugging while the chip is in the target system.

=== debugWIRE ===
{{Main|debugWIRE}}
[[debugWIRE]] is Atmel's solution for providing on-chip debug capabilities via a single microcontroller pin. It is useful for lower pin-count parts which cannot provide the four "spare" pins needed for JTAG. The JTAGICE mkII, mkIII and the AVR Dragon support debugWIRE. debugWIRE was developed after the original JTAGICE release, and now clones support it.

=== JTAG ===
The Joint Test Action Group ([[JTAG]]) feature provides access to on-chip debugging functionality while the chip is running in the target system.<ref>{{cite web|url=http://www.avrfreaks.net/index.php?module=FreaksArticles&func=downloadArticle&id=17|title=Guide to understanding JTAG and security fuses on the AVR|access-date=2012-09-19}}{{Dead link|date=July 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> JTAG allows accessing internal memory and registers, setting breakpoints on code, and single-stepping execution to observe system behaviour.

Atmel provides a series of JTAG adapters for the AVR:

# The Atmel-ICE<ref>{{cite web|url=http://www.atmel.com/tools/atatmel-ice.aspx|title=Atmel-ICE - Atmel Corporation|publisher=Atmel.com|access-date=2015-09-11}}</ref> is the latest adapter. It supports JTAG, debugWire, aWire, SPI, TPI, and PDI interfaces.
# The JTAGICE 3<ref>{{cite web|url=http://www.atmel.com/dyn/products/tools_card.asp?tool_id=17213&category_id=163&family_id=607&subfamily_id=2138|title=JTAGICE 3- Atmel Corporation|publisher=Atmel.com|access-date=2012-09-19}}</ref> is a midrange debugger in the JTAGICE family (JTAGICE mkIII). It supports JTAG, aWire, SPI, and PDI interfaces.
# The JTAGICE mkII<ref>{{cite web|url=http://qaswww.atmel.com/tools/avrjtagicemkii.aspx|title=AVR JTAGICE mkII|work=Atmel|url-status=dead|archive-url=https://archive.today/20130215133712/http://qaswww.atmel.com/tools/avrjtagicemkii.aspx|archive-date=15 February 2013|access-date=13 January 2013}}</ref> replaces the JTAGICE and is similarly priced. The JTAGICE mkII interfaces to the PC via USB, and supports both JTAG and the newer debugWIRE interface. Numerous third-party clones of the Atmel JTAGICE mkII device started shipping after Atmel released the communication protocol.<ref>{{cite web|url=http://www.atmel.com/dyn/resources/prod_documents/doc2587.pdf |archive-url=https://web.archive.org/web/20050516182708/http://www.atmel.com/dyn/resources/prod_documents/doc2587.pdf |archive-date=2005-05-16 |url-status=live|title=JTAGICE mkII Communication Protocol|access-date=2012-09-19}}</ref>
# The AVR Dragon<ref>{{cite web|url=http://www.atmel.com/tools/avrdragon.aspx|title=AVR Dragon|work=Atmel|access-date=13 January 2013}}</ref> is a low-cost (approximately $50) substitute for the JTAGICE mkII for certain target parts. The AVR Dragon provides in-system serial programming, high-voltage serial programming and parallel programming, as well as JTAG or debugWIRE emulation for parts with 32&nbsp;KB of program memory or less. ATMEL changed the debugging feature of AVR Dragon with the latest firmware of AVR Studio 4 – AVR Studio 5 and now it supports devices over 32&nbsp;KB of program memory.
# The JTAGICE adapter interfaces to the PC via a standard serial port.<ref>{{Cite web|url=http://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-42710-AVR-JTAGICE-mkII_UserGuide.pdf |archive-url=https://web.archive.org/web/20170702215107/http://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-42710-AVR-JTAGICE-mkII_UserGuide.pdf |archive-date=2017-07-02 |url-status=live|title=AVR JTAGICE mkII User's Guide|website=microchip.com|access-date=25 March 2020}}</ref> Although the JTAGICE adapter has been declared "[[End-of-life (product)|end-of-life]]" by Atmel, it is still supported in AVR Studio and other tools.

JTAG can also be used to perform a [[boundary scan]] test,<ref>[http://atmel.com/dyn/corporate/view_detail.asp?ref=&FileName=JTEGICE.html&SEC_NAME=product JTAGICE Press Release, 2004.] {{webarchive|url=https://web.archive.org/web/20110707183223/http://atmel.com/dyn/corporate/view_detail.asp?ref=&FileName=JTEGICE.html&SEC_NAME=product|date=2011-07-07}}</ref> which tests the electrical connections between AVRs and other boundary scan capable chips in a system. Boundary scan is well-suited for a production line, while the hobbyist is probably better off testing with a multimeter or oscilloscope.