What is a Boundary scan?
Boundary scan refers to a testing technique and methodology that involves building specific circuitry into an integrated circuit (IC) to facilitate testing, maintenance, and support of assembled printed circuit boards (PCBs).
Here are the key points related to boundary scan:
Design-for-Testability (DFT)
In VLSI (Very Large Scale Integration) design, where integrated circuits are highly complex, the concept of design-for-testability is crucial. It means that considerations for testing should be integrated into the design process from the beginning.
Limited Controllability and Observability
Testing a circuit requires the ability to access internal nodes for injecting test signals (controllability) and monitoring responses at internal nodes (observability). Unlike a printed circuit board, an integrated circuit has limited controllability and observability.
Registers and Scanning Shift Register
To enhance testability, registers can be strategically placed at critical testing points within the circuit. These registers can then be cascaded into a scanning shift register. This configuration enables the control and observation of internal signals during testing.
Boundary Scan Standard
Boundary scan takes the concept of enhancing testability a step further by introducing a standardized approach. The IEEE standard 1149.1 defines the boundary scan standard. This standard involves incorporating specific circuitry at the boundaries of the IC to enable efficient testing, maintenance, and support of assembled PCBs.
Assistance in Board-Level Testing
Boundary scan is particularly useful in the context of assembled printed circuit boards. It assists in testing not only individual ICs but also the interconnections and functionality of the entire board.
The objective of Test Scheme Development
The ultimate goal of developing a test scheme for a circuit is to identify the smallest set of test vectors (input combinations) necessary to verify the circuit functions. This is crucial, especially for large and complex circuits, where exhaustive testing (testing all possible combinations) is not feasible.
In summary, boundary scan is a testing methodology that involves incorporating specific circuitry and standards into integrated circuits to enhance testability, particularly for complex VLSI designs. It plays a significant role in ensuring the reliability and functionality of circuits during the testing phase and throughout their operational life.