Microprocessor-controlled systems rely on precise, lightning-speed manipulation of binary bits. One misplaced data, address, or instruction bit caused by a programming error or faulty component can render the entire control scheme useless. Consequently software-based products require the use of specialized instruments for testing incoming LSI devices, for developing software, and for field maintenance. This article, describes microprocessor development aids (MDAs) and logic analyzers, which play particularly vital roles in software design and integration with hardware.