Portable PXI Bus Digital Circuit Board Test and Diagnosis System

　　Since the 1950s, with the development of microelectronics technology, communication technology and computer network technology and the widespread application of large-scale integrated circuits, the maintenance of digital circuit faults in electronic equipment has become more and more complicated, and the testing difficulty has become increasingly greater. At the same time, the testing and diagnosis research of digital circuits has also made breakthrough progress. The pseudo-exhaustive method, Boolean difference method, characteristic analysis method, random test method, D-front sensitization method and causal function method belonging to the test generation algorithm of combinational circuits, the time frame expansion method and simulation-based method belonging to the test generation algorithm of sequential circuits, etc., have made the diagnosis theory of digital systems more perfect. However, the calculation work of digital circuit fault diagnosis is complex, the test overhead is huge, and there are still many difficulties in engineering practice. Therefore, how to use these theories and test methods to perform fault diagnosis better and faster is a problem that needs to be solved urgently. The development of automatic test equipment (ATE) is a revolution in testing technology, which has brought about the maturity of test equipment and provided new prospects for the application of test diagnosis theory in engineering.

　　Aiming at the development demand of digital circuit automatic test system, Aerospace Measurement and Control Company focuses on the test of more complex sequential circuits in digital circuits, takes digital circuits containing CPU, FPGA, etc. as test objects, and combines the currently commonly used sequential circuit simulation methods to successfully develop a portable automatic test system based on PXI bus technology (HTEDS8300 portable PXI bus digital circuit board test and diagnosis system). The system has the characteristics of high cost performance, small size, easy to carry, and low difficulty in TPS development. It is suitable for the design verification, testing and maintenance of semiconductors, aerospace/defense, communications and consumer electronic products in the military and civilian fields. The following specifically introduces the hardware and software composition and characteristics of the HTEDS8300 portable PXI bus digital circuit board test and diagnosis system, and uses the system to realize the automatic test of digital circuit boards containing CPUs.

　　PXI (PCI Extensions for Instrumentation) is a PC-based modular instrument platform for measurement and automation systems. It combines the electrical performance of the PCI bus with the rugged, modular, and European mechanical characteristics of CompactPCI, and adds hardware features such as trigger bus and local bus suitable for instrument use, making it a high-performance, low-cost development platform for measurement and automation systems. The HTEDS8300 portable PXI bus digital circuit board test and diagnosis system uses a PXI chassis embedded controller, with a light and compact structure and is easy to carry.

　　This system adopts the functional test method, directly using the input and output interfaces of the circuit as the excitation point and response point, and determines whether the board under test is working properly by comparing with the expected response, and locates the fault to the minimum replaceable unit. For the internal nodes in the circuit board, they can be connected through fixtures, probes and other equipment.

　　The system is equipped with 4 digital I/O modules for sending and collecting digital signals of digital circuits. Considering that a general CPU circuit board contains at least 32-bit address lines and 32-bit data lines and other control lines, the system is equipped with 104 digital I/O channels with a maximum data rate of 50MHz, which can be expanded to 352 channels at most. When testing digital circuit boards containing CPUs and FPGAs, the test port needs to change direction according to the timing. The test system has the ability to test the direction of real-time dynamic input and output, and can perform real-time hardware comparison of the collected response data.

　　Currently, most digital circuit boards are equipped with chips with boundary scan ports. In order to meet the testing requirements of such circuit boards, the system provides a boundary scan test channel that complies with IEEE1149.1.

　　In addition, the system is equipped with a digital oscilloscope module. This is mainly because in digital circuit testing, especially in high-speed digital circuit testing, an oscilloscope is needed to observe dynamic waveforms and measure characteristic values ​​such as waveform rise/fall time, so as to provide a basis for fault diagnosis. The test system is also equipped with a 6.5-digit digital multimeter that can measure voltage, current, resistance, inductance, capacitance and impedance. In this way, different resources in the system such as digital I/O and oscilloscope can work synchronously during testing, and the automatic test method is more flexible and diverse, which can meet the user's testing needs for complex digital circuits.

　　The system is equipped with an external circuit board test fixture, which can be freely rotated 180 degrees, so that the tester can fix the circuit board and flip the circuit board to measure both sides of the circuit board when analyzing and testing the circuit board.

　　The system is suitable for testing and diagnosing various types of digital circuit boards, and can isolate and locate the fault to the smallest replaceable unit (component) where the fault occurs. The test scope includes: medium and small scale integrated digital circuit PCBs; medium and small scale programmable logic series chips; large-scale integrated circuits with boundary scan interfaces, CPU chips, DSP signal processing circuit PCBs, and other types of digital circuit PCBs.

　　The system software is mainly composed of 7 parts: test and diagnosis program (TPS) development, test and diagnosis program execution, comprehensive query, information sharing, system maintenance, system security, and online help. It can realize the development and execution of test and diagnosis programs for various types of PCBs. The system completes the fault detection and location of PCBs through the information obtained through testing and the analysis and judgment of the test and diagnosis program.

　　In order to enable circuit board testers and maintenance personnel to break the tradition of completing circuit board test and diagnosis by writing code programs and reduce the technical difficulty of developers editing TPS, the software platform adopts a graphical TPS editing environment, providing a universal development environment that can complete the development, debugging and operation of TPS for different types of circuits. The system software can use the standard IEEE1445 format data output by digital circuit simulation software to test circuit boards, thereby improving the work efficiency and development quality of TPS developers.

　　The software platform provides a visual interface wizard function. By using the various process modules provided by the platform in conjunction with the corresponding functional components, users only need to input expert knowledge and other necessary information to establish a specific diagnostic program. Developers can complete TPS development without learning and performing complex source code, avoiding the drawback of one circuit module corresponding to one set of diagnostic software in the past, and having strong versatility and scalability.

　　At present, most digital circuit board test systems are basically used to test and diagnose digital circuit boards without CPU and FPGA. The common point of these circuit boards is that the response and stimulus correspond one to one, that is, the program controls the automatic test equipment to input signals to the circuit board. When the input of the circuit board is determined, the circuit board generates a corresponding output signal. According to this fixed input-output relationship, it is easy to judge the fault of the circuit board and the fault node. However, for circuit boards with microprocessor devices, this test method cannot be simply used to perform fault detection on ATE equipment. Since the microprocessor uses three buses or programming ports to control the circuit, the timing of the input and output of this type of circuit board is not fixed, which leads to the fact that each input stimulus and output response may not correspond one to one. In view of this problem, when judging the fault, the bus signal or port signal must be reliably controlled to ensure that each time is a synchronous test, that is, to ensure that the timing of each input stimulus signal is consistent. In this way, when comparing with the expected response signal, the fault will not be wrongly judged due to the difference in timing.

　　The control signal of the microprocessor is actually a digital signal, and the test system can provide more than 104 dynamic I/O signals. Therefore, the I/O signals of the test system can be used to simulate the signals of each pin of the microprocessor and drive other functional modules in the circuit, thereby simulating the timing of the microprocessor device, completing the purpose of synchronous testing, and effectively detecting the faults of other functional modules. If other functional modules are normal but the circuit board cannot work, the fault can be located on the microprocessor.

　　Take a CPU equipment board as an example to verify the I/O test capability of the system. The CPU of the circuit board controls the FLASH, temperature sensor and drive motor through the serial and parallel bus.

　　

　　Circuit diagram

　　The platform can select the I/O signal level voltage, change the I/O signal direction every cycle, edit the test stimulus and response signal in the graphical development environment provided by the software, and collect the response signal to test the circuit board in an interactive way. The system can accurately locate the circuit board fault and effectively improve the test efficiency.