1. CSCI-100 Introduction to Computing
Circuit Design
Example

2. 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

3. 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

4. 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

5. 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

6. Circuit Construction Algorithm
(Algorithm and Example DONE IN CLASS)

7. 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