What Is a JTAG Test and Why You Need to Know

Posted on September 2, 2020

Formed in 1985, Joint Test Action Group (JTAG) developed a method of verifying designs and testing printed circuit boards after manufacture. This method would later become the industry standard. Known as a JTAG test, the Standard Test Access Port and Boundary-Scan Architecture, or IEEE Standard 1149.1-1990, defines the structural description of testability features and how they may be used.

Debugging software

JTAG testing provides a means for testing connections on printed circuit boards or sub-blocks inside an integrated circuit. JTAG is an essential tool for debugging embed systems with no other resources. The process watches integrated circuit pin states, measures voltage, and analyzes the sub-blocks within the integrated circuit.
Available from the first instruction after CPU reset, JTAG assists in developing boot software. Furthermore, software developers can debug the software directly at the machine instruction level or high-level language source code.


The major advantage of the JTAG test is the ability to set and read the values on pins without direct physical access.

Boundary-scan supports the following board-level test functions:

• Interconnect wiring on a printed circuit board for shorts, opens and bridging faults
• Clusters of non-boundary scan logic
• Identification of missing, incorrectly oriented, or incorrectly selected components
• Identification of fixture problems
• Limited testing of individual chips on a board


ProScan speeds the debug process by eliminating the guesswork. With a graphical presentation, developers are provided an easy to read map. The display shows all pins and vectors, using different colors to differentiate between driving and receiving values and failures. The diagnostic messages appear on the screen alerting users of failures. These failures can be located directly from the message box by clicking on the specific alert.
ProScan is then used to further investigate any failures.
With a built-in netlist browser, users can delve deep into the test, interacting with pins, and set guards on pins if needed. Once all changes are made, recompile and run tests are handled by ProScan.

For more information on our cutting edge JTAG test, contact the professionals at Flynn Systems (603) 598-4444.