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What is boundary scan test? And why should you use it on your next design? In the next few minutes we will answer these questions by giving you a clear understanding of the power of boundary scan. You will discover why it is the preferred test method for a wide variety of applications. This educational technical video was created by TechSharpen in collaboration with Flynn Systems, the creators of the onTAP boundary scan automation software. Historically, the most straight-forward way to test electronic systems has been functional test. As the name implies, it means exercising a system as it is expected to be used in the target application. Though this approach continues to have merit, it has some significant drawbacks. First, it may be difficult to replicate a functional setup that sufficiently mimics the end application. Second, sufficiently testing the operational space of systems, with even moderate complexity, can be very difficult. An alternative to verifying functional operation is structural testing. This method tests individual partitions instead of looking at the system as a whole. It enables a more thorough testing that can verify corner cases which are difficult to access using functional test only. Structural test also has problems to overcome. Gaining access to internal nodes is a challenge. One traditional method for accessing internal nodes is employing a fixture with multiple electrical contacts, touching down on exposed metallic pads. This fixture is commonly called a "bed of nails." Unfortunately these fixtures are costly to fabricate and difficult to make a solid connection when there are many points to access simultaneously. This method becomes even more problematic as circuit technology shrinks, with a higher reliance on multiple-layered boards. It makes internal access almost impossible as nodes are buried under packages such as ball grid arrays. Boundary scan is an ingenious approach to structural testing that overcomes these challenges. Instead of relying on mechanical connections for access, it adds dedicated test circuitry to the system's ICs, using special registers inserted at the I/O pins. These registers can observe data on the I/O pins, and they can be used to override drive signals, providing test stimulus to the circuit. It is this combination of stimulating and observing internal nodes that provides a powerful mechanism for accurate structural testing. To gain test access to these registers, there is a separate serial data chain, independent of the functional paths. Test set-up information flows into the chain's input, propagating to the chain's output. If there are multiple ICs with boundary registers, they can be concatenated to make a longer chain. This same data chain is also used to off-load measured data. Typical boundary scan registers can have four different types of operations. One operation allows data to pass through the registers "transparently," without modification. This is the typical state of the circuit during normal functional operation. Another operation "captures" data coming into the register, without changing its value. This is how test data is observed. A third operation "updates" the output of the register,...