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This note describes the microdiagnostic approach being used on the Standard Computer MLP-900 processor. This machine is microprogrammable and designed for general-purpose emulation, simulation, and interpretation. As a consequence it has a number of features that make it unusually well suited for the application of microdiagnostics. These include a READ-WRITE control memory, one clock microinstructions, a general-purpose microinstruction repertoire, almost complete microprogram access to the hardware, and the ability to specify test operands as immediate values. These features plus the highly encoded form of microprogramming used greatly facilitate the design and programming of component-oriented test programs. This results in a microdiagnostic which is very compact, has a very short execution time, and requires a relatively short development time. Other advantages include a relatively low hardcore, very thorough testing, and high fault resolution.