The example schematic of the figure below shows a simple, one-board UUT.
Example UUT Schematic
The first step is to map various UUT states and modes. A counter provides two MSBs (most significant bits) for addressing a 64x4 bit static RAM (random access memory). RAM I/O (input/output) data share lines D0 – D3. The four address LSBs (least significant bits), A0 – A3, are inputs.
When UUTs are powered on, they can be in an unpredictable state. They must be initialized to a known state before testing can begin. Procedures for initialization are specific to each UUT design. Generally, all memory elements that affect the test must be initialized to set the UUT to a known state. In this example, initializing the board is achieved by initializing the counter. A vector is then applied to the inputs to test all board functions.