Class Notes (806,584)
CSC258H1 (46)
Lecture

CH 1 - Logic Gates and Transistors

5 Pages
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School
University of Toronto St. George
Department
Computer Science
Course
CSC258H1
Professor
Steve Engels
Semester
Winter

Description
INTRODUCTION  Assuming that certain signals can be turned on (ONE) or off  Course Goals (ZERO), we need to have ways to combine these singals together o Understand the underlying architecture of computer systems o Learn how to use thisarchitecture to store data and create  every electronic device combines input signals to behaviour. create output signals o Use the principles ofhardware design to createdigital logic  Ex. Ctrl Alt Del: if the Ctrl, Alt, and Delete buttons are solutions to given problems. being pressed, restart the computer  Linking hardware an software Ctrl Alt Del Restart o Everything is 1’s and 0’s 0 0 0 0 o int: 0 0 1 0 (demical) 1234  (binary) 11000000111001 31 31 0 1 0 0  By default ints are 32 bits long, 2 positive values, 2 0 1 1 0 negative values 1 0 0 0  Total 2 integers 1 0 1 0  Singed Integers: range from 2 to 2 -1 32 1 1 0 0  Unsinged Integers: range from 0 to 2 -1 1 1 1 1  Different ranges for long, short, and byte o if statements:  Ex. Train signals: if three train tracks converge onto a if value: single track, only turn on the green light if a single track has a train waiting # what is value “True”? T1 T2 T3 GO  False usually is 0, True usually is 1  If value is long and is 0.0 then it evaluates to false 0 0 0 0  Different data type, different requirements for T/F 0 0 1 1 0 1 0 1 o Power buttons 0 1 1 0  On & off are just binary singals  Eletrical signals 1 0 0 1 o The “ONE” and “ZERO” notations denotes high low voltage applied 1 0 1 0 1 1 0 0 between two points 1 1 1 0  ZERO: little to no voltage across the points  ONE: typically, a voltage difference of 5 volts  Logic gates o for integers, read 32 signals, determine high/low as 1/0 to produce o Complex circuits aren’t drawn as switches  Diagrams with switches are horrible to read and draw a number  Only an abstraction for what really happens anyways o Instead, logic gates are created to embody certain common digital logic combinations  Represented by their truth tables  Certain gate functions conincide with typical Boolean operators:  AND, OR, NOT, XOR o AND gate i.e. A AND B o Controlling Signals  typically change the voltage value that’s measured at a particular point through use of switches and/or gates A B Y 0 0 0 0 1 0 1 0 0 1 1 1 o Combining singals  Switches are physical devices for manually closing a circuit to control singals o OR gate i.e. A OR B  Gates are semi-conductor devices that close a circuit A B Y electrically 0 0 0 0 1 1 1 0 1 1 1 1 o NOT gate i.e. NOT A o Buffer A Y 0 1 A Y 1 0 0 0 1 1 o NAND gates are the most commonly-used gates in most circuits o XOR gate i.e. (A OR B)  Cheaper and smaller to fabricate  AND/OR combinations can be expressed entirely by NAND gate circuits o Multiple-input logic gates are permitted  more switches in eries or in parallel A B Y  NOT is just NAND with both inputs the same o Little circles denote an inverted signal but only when directly 0 0 0 adjacement to a gate’s input or output lines 0 1 1 1 0 1  these are equivalent: 1 1 0 o Creating complex circuits o NAND gate i.e. NOT (A AND B)  creating circuit logic is the same as working with boolean logic in Python, C or Java  Y = (!A AND !B AND !C) or (!A AND B AND C) or (A AND B AND C) A B Y 0 0 1 0 1 1 1 0 1 1 1 0 o Expressing Digital Logic  Given a logic circuit, determine the truth table that describes its behavior  Sometimes illustrated using a waveform o NOR gate A B C Y 0 0 0 0 0 0 1 1 A B Y 0 1 0 1 0 0 1 0 1 1 1 0 1 0 1 0 0 1 1 0 0 1 0 1 1 1 1 0 1 1 0 0 1 1 1 0  Digital logic tasks o Given a truth table determine the circuit that creates it o Look at the conditions that cause high output singals o Express the high conditions as a boolean statement, then covert this to gates TRANSISTORS  Conductivity of materials  Transistors Introduction o Eletricity can flow freely through a solid if there are free valence o Transistors form the basic building blocks of all computer hardware electrons in outter layer after the solid is formed  Allowed logical devices  modern computer o Elements’ conductivity depending on # eletrons in the it’s valence o Used for applications such as amplification, switching and digital logic shell and orbit of the valence shell design.  Eletroncs entering a material on one side traverse through the  Where do transistors fit elements through the valence shell o LOGIC GATE (made from) Transistors (based on) pn-  By exchanging positions with valence electrons of junctions (made from) Semiconductors elements  exit electron != initial electron  pn-junctions = a junction made from 2 materials a “p” and a “n”  Elements w/ full valence shell = not conductors  Eletricity Introduction  Higher outter orbit better flow b/c less attraction force from o Electricity is caused by the flow of charged particles, usually electrons protons in neucleus  Some materials allow flow better than others  Carbon bonds closer b/c lower outter orbit  ex. Metals vs. Rubber/Plastic (disallow eletrons to flow)  Silicon bonds further b/c higher outter orbits o Particle flow from of high electrical potential regions to low  Both have 4 eletroncs in the valence shell, shares w/ 4 electrical potential other of the element to complete orbit, but silicon  Similar to gravitational potential materials are better conductors o This potential is referred to as voltage o Semiconductor materials (silicon, germanium) straddle the boundary  How much electrical potential is in a source between conductors and insulators  Group = 0 V, charge energy are compared vs. the ground  behaving like one or the other, depending on factors like  Charges above 0 V (high voltage) wants a path to the ground temperature and impurities in the material (low voltage) o The rate of this flow is called the current  Eample Circuit Design o Circuit diagrams are composed of:  Sources  Voltage source & Current source
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