CSCI-100 Introduction to Computing Circuit Design Example

Abstraction in hardware design A transistor is too elementary a device to act as the fundamental design component Map hardware devices to Boolean logic by using AND, OR, and NOT gates as the building blocks This seemingly minor change in viewpoint (from transistors to gates) has profound effect on how computer hardware is designed and built We no longer need deal with anything electrical We no longer require knowledge of transistors, voltages, or currents Design more complex devices in terms of logic, not electronics Conversion from logic to hardware design can be automated

FROM LAST CLASS Gate The term gate suggests a simple circuit that controls the flow of electricity In the case of a NOT gate, the flow of electricity is manipulated so that the output signal is always opposite of the input signal We can think of a gate as computing a function of binary values 0 represents no current; 1 represents current symbol to the left (triangle w/ circle) used to denote NOT gate truth table to right describes mapping of input to output

Many other simple circuits can be defined to perform useful tasks FROM LAST CLASS Many other simple circuits can be defined to perform useful tasks AND gate – produces voltage on its output wire if both input wires carry voltage OR gate – produces voltage on its output wire if either input wire carries voltage AND, OR, and NOT gates can be combined to construct all the circuitry required to store and manipulate information within a computer

Circuits A circuit is a collection of logic gates Transforms a set of binary inputs into a set of binary outputs Values of the outputs depend only on the current values of the inputs

Circuit Construction Algorithm (Algorithm and Example DONE IN CLASS)

Example: Design a circuit (using AND, OR, and NOT gates) that implements a “Two or More” function with three inputs. This circuit is given three 1-bit values, a, b, and c as input. It outputs a 1 if at least two of its inputs are 1. Otherwise, It outputs a 0. (DONE IN CLASS) 7