In 1990, the IEEE 1149.1 standard formally defined the approach, specifying the four signal lines (TDI, TDO, TMS, and TCK – data in, data out, mode select and clock) and the behaviour of the Test Access Port (TAP) controller. Boundary scan allows test data to be shifted into and out of a device, enabling test software to stimulate and observe circuit behaviour without requiring physical access to component leads. By cycling through various signal combinations on the pins, the system can detect shorts, opens, and stuck-at faults across accessible nets.
One of the key benefits of boundary scan is that, since it eliminates the need for physical probing, test points can be removed – it only requires the four TAP signals to be available on a connector. Additionally, the tests are swift, typically taking around a minute for interconnect tests and functional tests of some devices. Multiple JTAG devices can be daisy-chained, allowing them to share a single set of TAP connections or they can be placed on separate scan chains for increased speed. With these methods, access can be gained to all JTAG devices, maximising test coverage on the board.
XJTAG’s suite of tools provides a comprehensive system to setup and execute boundary scan testing:
–XJDeveloper guides users through board setup, provides statistics on test coverage, and supports functional testing of components like LPDDR, eMMC, and flash memory.
–XJRunner enables tests created in XJDeveloper to be run in production environments without exposing editable project files, preserving design IP.
–XJAnalyser allows live control and observation of individual JTAG pins, helping engineers quickly confirm fault locations.
Boundary scan continues to evolve. Standards such as IEEE 1149.6 extend testing capabilities to high-speed differential and AC-coupled signals, another area supported by XJTAG’s platform. Additionally, as JTAG adoption grows in sectors such as aerospace, automotive, and communications, the complexity and number of JTAG-enabled devices on boards are increasing. XJTAG has responded with tools like the XJLink-PF40, which supports up to 8 simultaneous JTAG chains in four voltage domains, offering scalable performance for larger designs.
JTAG was developed to solve a real engineering problem: how to reliably test modern, complex PCBs without relying on physical access. Since its standardisation, it has become a foundational tool in the electronics manufacturing and validation process. XJTAG gives you the tools you need to use the built-in capabilities in your devices to maximise your test coverage.
If you would like more information on XJTAG or would like to sign up for a free trial, please get in contact with them here: XJTAG.com/contact
