Abstract: An automatic test equipment for the functional testing of electrical printed circuit board assemblies is constructed as the combination of a programmable controller based upon a microcomputer and selected interface modules which can be plugged into the controller system backplane in any of a number of module interconnection locations and in any combination of module types with the controller being adapted to interrogate the modules as to their type and location and organize its routines accordingly. The controller has an advantageous bus structure for resource sharing within the equipment, and provides facilities for various forms of input/output modules as well as for analog stimulus/response modules, programmable waveform generator modules, signature analysis and frequency measurement modules, real time emulation modules, etc., and for the connection of computer standard utilities such as keyboard, light-pen graphics, printer, etc.