Embedded Systems Circuits and Programming

Chapter 3

Logic Gates and Circuit Components

3.1  Logic Gates

A logic gate can be a virtual or a physical device. In either case the logic gate takes one or more binary signals as input and produces a binary output as a logical function. The basic logical operations of AND, OR, XOR, and NOT are described in basic electronics and Boolean algebra texts. Although logic gates can be made from electromagnetic relays, mechanical switches, or optical components, nowadays they are normally implemented using diodes and transistors.

Charles Babbage’s Analytical Engine, devised around 1837, used mechanical logic gates based on gears. Electromagnetic relays were later used for logic gates, and these were eventually replaced by vacuum tubes, as Lee De Forest’s ...