Application of real-time simulation for test

In-circuit testing is a mature technology, yet it has compromising issues. One issue is the application of device test programs from a program library. These programs are viable for testing components in free air, but adjustments are often required when applying these tests to a device on a populated circuit board. Such test modification, such as test pruning and arbitrary masking, frequently reduces the quality of test. One way to resolve this shortcoming is through the use of a real-time software reference model. During testing, the software model receives information about device interconnections and tied pins. The test software then runs the device test program against both the software model and the actual device. The software model results are then compared to the device measured results to determine if the test passed or failed. The key advantage of this technique is that component testing may be performed in-circuit without knowledge of how the device is connected in the circuit. This is extremely useful for testing assemblies that have little or no support documentation. This paper describes the technical details of this approach, its implementation in a test instrument and the results of its application.