Editing AVR microcontrollers (section)

=== 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.