Boundary Scan In Fault Diagnosis Of Digital Circuits

With the increasing scale of digital circuits, the electric systems become more and more complex, and difficulty of fault diagnosis has been improved. The fault diagnosis technology has become a popular subject.The paper first introduces the theory and basic concepts of fault diagnosis in digital circuits, and explains the diagnosis methods of multiple faults in digital circuits. In combinational circuits system, we mainly study pseudo exhaustive method and fault table method by example; in sequential logic circuits system, we mainly study circuit test method and conversion checking method by example. And the difficulties in fault diagnosis of sequential logic circuits are analyzed.After that the paper discusses about the basic theory and method of boundary scan in fault diagnosis. Then the paper focuses on basic structures in boundary scan, including TAP controller and main registers. Then it analyses several common algorithms. The advantage of conventional algorithm is easy to test and code. The disadvantage is that fault diagnosis test is time-consuming and complicated, and its fault diagnosis ability is poor. Conventional algorithms include shift algorithm, binary algorithm, modified counting sequence algorithm, compensation algorithm. Relatively "smart" algorithms, such as the w-step adaptive algorithm and Gann test vector generation algorithm, combine with relevant information. These algorithms greatly reduce the number of test vectors, and shorten the test time, but need longer test time at the same time.Then from the points of both device and system, the testability of boundary scan is studied. The testability of the device depends on whether the device supports boundary scan. When it comes to the system, every system has some devices which don’t support boundary scan, we can connect them with devices which support boundary scan or external digital I/O devices. So the boundary scan chain connects both devices which support boundary scan and devices which don’t support boundary scan, and greatly improves the coverage of fault diagnosis in system.Finally, we design a boundary scan test system for a radar receiver. The software part covers from TAP controller test, boundary scan device self-test to boundary scan test. The hardware applies for multi types of digital circuits in radar receiver. The system is tested and proved to be right.