Introduction

JTAG*,* which stands for Joint Test Action Group, is a standard that defines a way to test and debug electronic circuits. It was created in the 1980s as a way to improve the testing and programming of printed circuit boards (PCBs) and has since become an essential tool for electronic design and manufacturing.

***JTAG*** allows for the testing and programming of digital and analog circuits, including microprocessors, memory devices, and other digital and mixed-signal components. The standard defines a set of signals that are used to perform various operations on the circuit, such as reading and writing data, controlling the circuit's state, and checking for faults.

The JTAG standard is implemented using a set of pins on the circuit, which are used to connect the circuit to a JTAG controller, also known as a JTAG probe. The JTAG controller is typically a specialized piece of hardware or software that is used to communicate with the circuit and perform the desired operations.

One of the key advantages of JTAG is that it allows for testing and programming of the circuit without the need for physical access to the individual components. This is particularly useful for circuits that are located on PCBs that are difficult or impossible to access, such as those that are embedded in a larger system or are part of a complex network of interconnected components.

JTAG also provides a way to test and diagnose faults in a circuit. The standard includes a set of tests that can be performed on the circuit to check for various faults, such as short circuits, open circuits, and other common problems. These tests can be run at any time during the development or manufacturing process, allowing for rapid identification and correction of any issues.

In addition to testing and debugging, JTAG is also used for programming of devices. Many microcontrollers and other digital devices can be programmed using the JTAG standard, allowing for rapid and efficient programming of large numbers of devices.

Overall, JTAG is an essential tool for electronic design and manufacturing, providing a way to test and program circuits in a rapid and efficient manner. While it is a complex standard that requires specialized hardware and software, it is widely used and supported by many different vendors and manufacturers, making it an important part of the modern electronic design process.

JTAG Technology

JTAG is commonly referred to as boundary-scan and defined by the Institute of Electrical and Electronic Engineers (IEEE) 1149.1, which originally began as an integrated method for testing interconnects on printed circuit boards (PCBs) implemented at the integrated circuit (IC) level. As PCBs grew in complexity and density—a trend that continues today—limitations in the traditional test methods of in-circuit testers (ICTs) and bed of nails fixtures became evident. Packaging formats, specifically Ball Grid Array (BGA) and other fine pitch components, designed to meet ever-increasing physical space constraints, also led to a loss of physical access to signals.

These new technology developments led to dramatic increases in costs related to designing and building bed of nails fixtures; at the same time, circuit board test coverage also suffered. JTAG/boundary-scan presented an elegant solution to this problem: build functionality into the IC to assist in testing assembled electronic systems.

Today, JTAG is used for everything from testing interconnects and functionality on ICs to programming flash memory of systems deployed in the field and everything in-between. JTAG and its related standards have been and will continue to be extended to address additional challenges in electronic test and manufacturing, including test of 3D ICs and complex, hierarchical systems.

History of JTAG