The book introduces the reader to the world of microprocessor technology in an accessible form. It contains materials covering various aspects of microprocessor design: from information about the simplest logical elements to a statement of principles for the development of microprocessor systems and quite complex multi-module programs for them. Of the variety of microprocessors, microcontrollers of the MCS-51 family are considered as an example. The choice is due to their prevalence, availability and support from major manufacturers such as Analog Devices and Texas Instruments. The described methods for developing microprocessor devices can also be applied when using microcircuits of other families. Much attention is paid to building the structure, principles of writing and debugging programs for microcontrollers in C and assembly languages. Ready-made templates for writing programs in assembler are provided and the features of using the C language for implementing specific devices are shown. In preparing the book, materials from lectures on microprocessors given by the author for a number of years at the Siberian State University of Telecommunications and Informatics were used. For a wide range of radio amateurs and programmers