Hardware Abstractions: Logic Gates

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In this lesson we will look at some additional examples of how the Big Idea of *Abstraction* is used in computing. We will focus on low-level hardware abstractions, in particular, on logic gates, the fundamental computational building blocks of electronic circuits. We'll take a first look "under the hood," so to speak, to see how computers process binary information.

Computers use Logic Gates to process a Boolean logic function on one or more inputs to produce a desired output. Studying the symbolic abstraction of logic gates through wiring diagrams and truth tables will assist students in understading the abstraction levels of computer programiming.

This unit will provide an interactive environment using a Logic Gate Simulator to help students grasp the various types of logic gates used in computers.

Make sure that you do the following:

- Click on the links for all of the gates
- Understand the truth tables
- Use the Logic Gate Simulator, using Toggle Switches, Wire, Gates, and a Light Bulb.
- Do the Self Check, including the AP Exam Question
- Make sure that you Update your Google Site

**Review** (Courtesy of "All About Circuits")
- AND Gate: Output is “high” only if first input and second input are both “high.”
- OR Gate: Output is “high” if input A or input B are “high.”
- NAND Gate: Output is not “high” if both the first and the second input are “high.”
- NOR Gate: Output is not “high” if either the first input or the second input are “high.”
- NAND Gate: A Negative-AND gate behaves like a NOR gate.
- NOR Gatge: A Negative-OR gate behaves like a NAND gate.
- XOR Gate: Output is “high” if the input logic levels are different.
- XNOR Gate: Output is “high” if the input logic levels are the same.