Design considerations and DFT to enable testing of digital interfaces

In the last 15 years, the specifications for digital interfaces have evolved significantly, from specifying only nominal or typical values to specifying extreme maximum or minimum values that are observable at the pins of the device to values that are not directly observable at the pins of the device. There has been a corresponding evolution of high volume manufacturing (HVM) testing methods. This tutorial paper summarizes the various digital interfaces specifications, the techniques used to test then, and the associated design considerations and design for test (DFT) circuitry. The example specifications and test data are from my experience on Intel Pentium-Pro, Pentium III and Pentium 4 microprocessors.