Storing and Organizing Data

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Storing and Organizing Data
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Why Do I Need to Understand How Data Is
Represented?

• In order to install, program,maintain, and
  troubleshoot todays PLCs, you must understand
  the different methods by which internal data is
  represented.

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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.

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PLC Words

• One measure of a computers capabilities is the
  length of the data words on which it can operate.
• Many current PLCs use 16-bit words.
• Many newer PLCs use 32-bit words.
• SLC 500 and PLC 5 family PLCs are 16-bit
  computers.
• Control Logix is a 32-bit computer.

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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.
• Controller
• The
• Monday

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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 Concept

• Two-state devices are described as either
  discrete or digital devices.
• Discrete or digital devices are simply either on
  or off.
• Binary is based on two states, on or off.

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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 word might look like
• 1010 1010 1010 1010 1010

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Information Represented as Combinations of Bits
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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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The Binary Number System Has the Following
Characteristics

• Two digits
• 0 or 1
• Base or radix
• 2
• Weights
• 1, 2, 4, 8, 16, 32, 64

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16-bit Binary Word Bit Weighting

• MSB LSB
• LSB least significant bit
• MSB most significant bit

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Binary Numbers Place Values
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Binary Number Weighting
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Decimal 0 through 7 Represented with Binary Bits
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Comparison of Decimal to Binary Numbers
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Parts of a 16-bit Word
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Bytes, Nibbles, and Bits
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PLC Data Formats

• Two 8-bit unsigned bytes of data
• 16-bit unsigned integer
• 16-bit signed integer
• 32-bit signed integer
• Binary coded decimal
• Hexadecimal

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Two 8-bit Unsigned Bytes of Data
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Hexadecimal
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16-bit Signed Integer
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16-bit Unsigned Integer
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32-bit Signed Integer (1 of 2)
Double Word
0 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0
0 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0
Lower 31 bits contain the value
Sign bit
32 bit signed integer data range
-2,147,483,648 to 2,147,483,647
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32-bit Signed Integer (2 of 2)
Double Word
0 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0
0 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0
Byte
Byte
Byte
Byte
Word
Word
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Basic PLC Data Types
Data Type Description Size Range
Bool Single bit Bit 1 ON 0 OFF
Sint 8 bits Byte -128 to 127
Int 16 bits Word -32,768 to 32,767
Dint 32 bits Double Word -2,147,483,648 2,147,483,647
Real Floating point Real or floating Point Larger than Dint or with Decimal point
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Data Table Format

• Words are 16 bits.
• Bits 0 through bit 15
• First word or bit is always 0.
• SLC 500 data tables can contain up to 256 words
  (0 to 255).
• PLC 5 data tables can contain up to 1,000 words
  (0 to 999).

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Words Arranged in a Data Table
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Status Table Words Assigned by Module
Requirements

• The number of status table words assigned depend
  on what a specific module needs.
• 16-point module equals 16 bits.
• 32-point module equals 32 bits.
• Four-channel analog equals four words.
• Eight-channel analog needs eight.

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SLC 500 I/O Configuration
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16-point Modules I/O Points Represented in a
Word
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Physical Input Conditions and the Corresponding
Input Data Word
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8-Point Input Module Represented in a Word
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SLC 500 Input Status Table
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24-point I/O Module Represented in Two Words
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Two Words Representing Inputs for a 32-bit Module
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Output Status File Correlation to Module
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SLC 500 Digital Outputs
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Four Words Representing a Four-channel Analog
Module
15 14 13 12 11 10 9
8 7 6 5 4 3
2 1 0
Channel 0
0 1 1 1 1 1 0 1 0 1 0 1 1 1 1 1
0 0 0 0 0 0 1 1 1 1 1 1 1 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1 0 0 1 1 1 1 1 1 1 0 0 0 0 0 0
Channel 1
Channel 2
Channel 3
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SLC 500 Analog Input Channels
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SLC 500 Output Analog Channels
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So, Whats in It for ME??

• I need to be able to work with different number
  systems.
• PLC configuration
• PLC troubleshooting
• Program interpretation
• Error code interpretation
• Data conversion to different hardware

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SLC 500 Analog Input Module Configuration

• You need to configure a 1747sc-INI4i analog input
  module.
• Module configuration specifications are listed
  below.

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Channel Configuration Word
Channel Data Word
SLC 500 Processor
Analog Input Module
Channel Status Word
Analog Input Signal
Channel Configuration
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Specifications

• Enable the input channel
• 4- to 20-mA input range
• Work in engineering units
• Pump to run maximum if open input
• 60-Hz input filter
• Auto calibration disabled

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What Do You Need to Do?

• Determine the 16-bit data word for the
  configuration.
• Convert the binary word into decimal.
• Program a move instruction on your SLC 500 ladder
  to move the configuration data to each analog
  channel.

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Input Channel Configuration Word
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(No Transcript)
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• What value will you enter into the move
  instructions source?

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Understanding Binary Coded Decimal (BCD)
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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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Binary Coded Decimal
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Two-digit BCD Thumb-wheel Interface
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Four-digit BCD Thumb-wheel
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Output Module Connected to Seven-segment Display
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Comparison of BCD to Decimal and Binary Numbers
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BCD Invalid Codes
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Decimal, Hexadecimal, and BCD Comparisons
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SLC 500 Conversion from BCD
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SLC 500 Converting to BCD
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PLC 5 Converting from BCD
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PLC 5 Converting to BCD