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Copyright © 2002 Delmar Thomson Learning
Chapter 4
Number Systems
Copyright © 2002 Delmar Thomson Learning
Objectives
Identify the commonly used number systems used in PLCs.
Convert binary data to decimal.Examine how data is stored in PLC
data tables.Describe how BCD field devices
interface.
Copyright © 2002 Delmar Thomson Learning
Why Do I Need to Understand How Data Is Represented?
In order to install, program,maintain, and troubleshoot today’s PLCs, you must understand the different methods by which internal data is represented.
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Number Systems Typically Used with PLCs
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We Use Words to Represent Information
Our words are groups of characters grouped together to represent something.
The words we use are of different lengths: ControllerTheMonday
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We Use Symbols Called Numbers to Represent Data
Everyday numbers are decimal.
12,345
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Computers Do Not Understand
Computers do not understand the words and numbers humans use.
Computers have their own language called binary.
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Binary Language
Binary information is also represented in groups of characters.
A group of BInary digiTs called bits can be organized into words.
Binary bits consist of only two characters: 1 and 0
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Binary Words
16 bits grouped together is called a word.
A binary would might look like:
1010 1010 1010 1010 1010
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Decimal Numbers
Ten Digits 0,1,2,3,4,5,6,7,8,9
Base or radix 10
Weights 1, 10, 100, 1000 …..
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Decimal Number System
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Sixteen-Bit Binary Word Bit Weighting
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Comparison of Decimal to Binary Numbers
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Decimal Place Value Equivalent
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Comparison of Decimal to Binary Numbers
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Four-Digit BCD Thumb-Wheel
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Comparison of BCD to Decimal and Binary Numbers
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Single-Digit BCD Thumb-Wheel Interfaced to a PLC
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Binary-Coded Decimal Number Bit Patterns
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Two-Digit BCD Thumb-Wheel Interface
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BCD Invalid Codes
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Thumb-Wheel Dialed to 11
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Thumb-Wheel Dialed to 743
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Output Module Connected to Seven-Segment Display
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Decimal 0 through 7 Represented with Binary Bits
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Octal Number System Place Values
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Decimal, Hexadecimal, and BCD Comparisons
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Place Values of Hexadecimal
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