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The story behind the JTAG standard: Why is this technology a game-changer for circuit board testing?
In the development and manufacturing of electronic products, ensuring the reliability and performance of circuit boards is critical. This is why Boundary Scan technology has become so important. The core of this technology lies in the IEEE 1149.1 standard developed by the Joint Test Action Group (JTAG) in 1990 and has since gained widespread acceptance. The JTAG standard not only changes the method of testing circuit boards, but also improves the efficiency of fault diagnosis, becoming an indispensable part of modern electronic design.
Boundary scan provides a method for testing interconnects without the need for physical test probes, by adding test cells on each pin.
Testing principle
Boundary scan's architecture allows for testing of printed circuit board interconnects, which is difficult to achieve with traditional test methods. By adding test cells on each external pin, these cells can selectively cover the functionality of the pin. This allows the test system to effectively apply signals to the pins and check the signal's correctness. If a short or open circuit occurs, the test system can quickly catch the problem, thereby reducing error rates.
Chip internal infrastructure
To provide boundary scan functionality, integrated circuit vendors add additional logic to their devices, including scan cells for each external interconnect. These scan units form an external boundary scan shift register and operate together with the JTAG test access port controller. This enables scanning between internal logic design blocks so that these integrated components can be tested as if they were separate chips on a circuit board.
The overlapping use of these internal scan chains is a common requirement in chip design.
Testing mechanism and operation methods
The boundary scan test mechanism allows the test system to feed data back to the test system through the clock for analysis. With modern dense circuit boards, the use of physical test probes has become increasingly difficult, however, boundary scan technology makes testing more efficient by providing on-demand access possibilities. Design testing has always been a major consideration in many chip designs, and boundary scan test vectors are often delivered in sequence vector format (SVF).
Circuit board test infrastructure
High-end commercial JTAG test systems are usually able to import design 'netlists' and boundary scan models from CAD/EDA systems to automatically generate test applications. These test systems can efficiently find faults in circuits, providing precise location of open or short circuits, and are often used in conjunction with other test systems. These commercial systems are expensive, but well worth the investment for professionals looking for efficient testing.
Application in fault diagnosis and development process
Boundary scan architecture also shows its advantages during the development phase of embedded systems. By turning a JTAG access port into a low-speed logic analyzer, developers can effectively observe and analyze system performance without relying on specialized hardware. This flexibility makes JTAG the tool of choice for many development and testing activities.
The importance of JTAG testing is not only reflected in the testing level, but also accelerates the process of product development and reliability assurance.
Historical background
Since James B. Angell proposed the concept of serial testing at Stanford University, many large companies have gradually realized the importance of testing technology, especially IBM's development of level-sensitive scan design (LSSD). These historical backgrounds laid the foundation for the development of JTAG boundary scan technology and became the widely used standard today.
Market status and future challenges
As electronic design continues to advance, JTAG and boundary scan technology still face new challenges, especially in emerging technology fields such as multi-chip packaging (MCP) and system-on-chip (SoC). How to continue to improve testing efficiency and ensure the testability of the design will be an important issue for the industry in the future.
In summary, the implementation of the JTAG standard not only changes the game rules of circuit board testing, it also redefines our understanding of the internal structure testing of devices. With the rapid development of technology, what innovative technologies will appear in the future to further improve the efficiency and reliability of testing?
