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# Chapter 5 - PowerPoint PPT Presentation

Chapter 5. Introduction to PLC Operation. Objectives. Explain what binary information is and how it is used in PLCs. Describe how computer and PLC data are represented. Examine PLC memory and how it is used. Explain how data gets into a PLC.

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Chapter 5

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## Chapter 5

Introduction to PLC Operation

### Objectives

• Explain what binary information is and how it is used in PLCs.

• Describe how computer and PLC data are represented.

• Examine PLC memory and how it is used.

• Explain how data gets into a PLC.

• Identify what addresses are and how they are used in PLCs.

### The PLC Is a Digital Computer

• The PLC is a computer similar to a desktop or notebook computer.

• A PLC is an industrially hardened computer.

### Binary Concept

• Binary is based on two states, on or off.

• Two-state devices are described as either discrete or digital devices.

• Discrete or digital devices are simply either on or off.

### Binary Data Representation

• We communicate to others using groups of letters arranged into words.

• The PLC uses groups of bits called words.

• Different bit patterns represent different information.

### Bits

• Unlike English, computers have only two characters available, 1 or 0.

• Each 1 or 0 is called a binary digit, or bit.

• Binary is base or radix 2.

• A single bit is the smallest unit of computer data.

### PLC Words

• One measure of a computer’s capabilities is the length of the data words it can operate on.

• Current PLCs use 16-bit words.

• Newer PLCs use 32-bit words.

• SLC 500 family PLCs are 16-bit computers.

### 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).

### Input Data File

• Each input screw terminal has one memory location to store on or off status.

• Input data is stored in the input data file, also called the input status file.

• Input status file holds input status information, which is used to solve ladder program.

### Input Data File (cont’d.)

• Identified as an I type data file.

• Only one input status file allowed per project.

• Only has words created for actual modules in system.

### Output Data File

• Each output screw terminal has one memory location to store on or off status.

• Output data is stored in the output data file, also called the output status file.

### Output Data File (cont’d.)

• Output status file holds output status information to update outputs.

• The result of solving the ladder program.

• Output data sent to modules during output update portion of scan.

### Output Data File (cont’d.)

• Identified as an O type data file.

• Only one output status file allowed per project.

• Only has words created for actual modules in system.

### PLC Data Formats

• Two 8-bit Unsigned Bytes of Data

• 16-bit Unsigned Integer

• 16-bit Signed Integer

• Binary Coded Decimal

### PLC Memory Categories

• PLC memory is divided into two categories:

• System memory

• Application memory

### System Memory

• Differentiates a PLC from another type of computer device.

• Gives PLC its personality.

• Programmed into PLC at factory.

• Also called its operating system.

### SLC 500 Operating System

• SLC 5/03, 5/04 and 5/05 processors have field upgradable operating systems.

• Fix problems.

### Application Memory

• Stores user program.

• Stores data associated with user program:

• Input status file

• Output status file

• Timers and counters

• Numerical data such as recipes

• Results of math operations

• Ladder files 3 through 255 are subroutines.

Output status

Input status

Processor status

Binary or bits

Timers

Counters

Integer

Floating point

User defined

### Default Data Files

• Data files O through 8 are created by the processor with new project.

• Floating point file is available on SLC 500 modular processors 5/03, 5/04, and 5/05.

• 5/03 processor must have operating system OS 301 and above.

### Data File Identification

• O:Output Status File

• I:Input Status File

• S:Processor Status File

• Cannot create additional O, I, or S data files.

### Data File Identification

• B3Binary or bit file

• T4Timers

• C5Counters

• R6Control

• N7Integer

• F8Floating Point

### User Configurable Files

• Data files greater than file 8 up to file 255 can be created by the user.

• These are user-defined files.

• B, T, C, N, F file types.

• Each file can contain up to 255 elements with adequate processor memory.