05-04-2012, 10:41 AM
Digital Logic Tutorial and Design
Digital Logic Tutorial and Design.ppt (Size: 142.5 KB / Downloads: 97)
Digital Logic Lab(A mini-lab experience)
We are going to build both a combination lock and a flashing railroad crossing signal 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
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
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:
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
NOT Operator/Inverter Gate
The NOT gate reverses the input
All digital computers are built using only three gate types: AND, OR, and NOT
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
Try the Excel spreadsheet exercise
Digital XOR
We can build an electrical device that performs the logical XOR operation on voltage equivalents of logic values
An XOR gate has the
electrical schematic:
Multi-Input AND Gate
AND gates can be built with any number of inputs
Consider the symbol for the 4-input AND gate
F is true only when all the inputs are true (1’s)
Using the Excel workbook “EE-WISE-DigitalLab”, open the “Digital Locks” worksheet, and test this circuit
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
The number of inputs could be increased by using more and more AND gates
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
Digital Combination Lock
Let’s build a combination lock whose input (key code) combination is 0 1 1 0
Is there any other combination that works?