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Digital Logic Tutorial and Design Lab1 Digital Logic Lab (A mini-lab experience) • We are going to build both a combination lock using digital logic devices • To build these circuits we will draw upon knowledge or resources developed by several areas of electrical engineering • First, we will need to learn a little about digital logic Some Definitions • Definition: Discrete System - a system with a finite number of sizes or measures – Shoes, Dresses, Pants, Bolts, Pencils • Definition: Digital System - a Discrete System with only two values of system variables: 1 and 0 – True/False; Yes/No; Male/Female; On/Off • Let’s compare digital and continuous (analog) systems – Digital signals are binary; analog signals are real-valued numbers – Digital is less susceptible to noise Analog Waveform Voltage (V) 5 Time 0 Digital Waveform 1 1 Voltage (V) 5 0 Time 0 4 Breadboard • A Breadboard is very useful for trying out new electronic circuits and for experimentation. Electronic components and integrated circuit (IC) chips can be plugged into the small holes and connected into temporary circuits. How Does a Breadboard Work The top row is linked horizontally (for the positive of the power supply) and the bottom row is also linked horizontally (for the negative of the power supply). The remaining holes on the breadboard are connected vertically in columns of five holes with no link across the gap across the horizontal centre of the breadboard. AND Operator • Let’s look at the relationship between the semantic and logical operator known as the AND operator • Consider: If the car is fueled AND the engine works, then the engine will start • AND means that both conditions must be true in order for the conclusion to be true 7 Digital AND • We can build an electrical device that performs the logical AND operation on voltage equivalents of logic values • An AND gate has the electrical schematic: A Inputs Output B For digital logic: True = 1 is 5 volts False = 0 is 0 volts • Practice with the Excel spreadsheet 8 OR Operator • Another basic operator is the OR • Consider: If I have cash OR a credit card, then I can pay the bill • OR works such that the output is true, if either of the two inputs is true 9 NOT Operator/Inverter Gate • The NOT gate reverses the input A • All digital computers are built using only three gate types: AND, OR, and NOT B NOT Operator Truth Table A B 0 1 1 0 10 XOR (Exclusive OR) Operator • Let’s look at the relationship between the semantic and logical operator known as the XOR operator • Consider a biological example: If gender A XOR gender B, then reproduction is possible • XOR works such that output is activated (equal to one) if both inputs are of a different value 11 Led(light emitting diode) Led is a semiconductor light source Red, yellow and green (unlit) LEDs used in a traffic signal Chips • Basic logic chips often come in 14-pin packages. • Package sizes and styles vary. • Pin 1 is indicated with a dot or half-circle • Numbers are read counterclockwise from pin 1 (viewed from the top) Pin 14 Pin 8 Pin 1 Pin 7 14 Chips • Chips require a voltage to function Pin 14 Pin 8 Pin 1 Pin 7 • Vcc is equal to 5 volts and is typically pin 14 • Ground is typically pin 7 15 Chips – Specification Sheet Voltage The voltage and ground pins must be connected for the device to function. Check the specification sheet to make sure. Ground Diagram from http://www.onsemi.com 16 Chips – Specification Sheet A B C D Diagrams from http://www.onsemi.com 17 Wiring a chip IN IN Vcc OUT Lab Exercise Vcc Probe 18 Lab Exercise • Using the experimenter’s boards, connect the circuit provided to you in the following pages. 19 Layout of the SK-10 Experimenter's Board 20 Layout of the SK-10 Experimenter's Board Flat Side 7400 Wires 21 Logic Diagram of Lab 22 Digital Combination Lock exercise 23 Multi-Input AND Gate • AND gates can be built with any number of inputs • Consider the symbol for the 4-input AND gate A B C D F • F is true only when all the inputs are true (1’s) 24 Digital Combination Lock • Using 3 two-input AND gates, we could build a combination lock that requires a four-digit code, specifically: 1 1 1 1 1 AND 1 1 AND 1 1 AND 1 1 • The number of inputs could be increased by using more and more AND gates 25 Digital Combination Lock • We could build a combination lock that only uses the AND gate, but that would be of little use since everyone would know our combination, namely 1 1 1 1 • To build a more interesting combination lock, we will utilize the NOT (inverter) gate 0 1 26 Digital Combination Lock • Let’s build a combination lock whose input (key code) combination is 0 1 1 0 0 1 AND 1 1 AND 1 1 AND 0 1 1 • Is there any other combination that works? 27 “Picking” a Digital Lock Use the truth table below to record the lock outputs for the different lock combinations. Input Combination A B C D 0 0 0 0 0 0 0 1 0 0 1 0 0 0 1 1 0 1 0 0 0 1 0 1 0 1 1 0 0 1 1 1 1 0 0 0 1 0 0 1 1 0 1 0 1 0 1 1 1 1 0 0 1 1 0 1 1 1 1 0 1 1 1 1 Lock #1 Lock Output Lock #2 Lock #3 Lock #4 Lock #5