Abstract: A programmable fault injection tool (PFIT) for the texting of the diagnostic capabilities of a computer or digital processing system is disclosed. The PFIT is made up of event compare hardware and error injection hardware.The event compare hardware of the PFIT is user programmable through menu-driven software to compare a particular stored event, either a digital word or sequence of words, with an event measured within the system under test. The stored event can be changed by the user under program control so as to provide a generalized fault injection tool. In addition, the tool includes a mask memory that allows certain bits in a word to be masked, or ignored, when the state of the bit within the word is inconsequential.The error injection hardware of the PFIT is controlled by the event compare hardware to inject faults by short circuiting voltage nodes within the system under test to ground or a supply voltage.