Chapter 03

Introduction to Chapter 03

Memory Structure & Organization

There are three basic types of memory structures and organizations: Address-based memory Tag-based memory Combination of Address/Tag-based memory

Memory Structure & Organization

There is no definitive standards in the way PLC/PAC manufacturers address memory; however, there are similarities.

When one system is learned, the other methods come fairly easily.

In this course we will be learning the basics of: Allen Bradley SLC-500 series / LogixPro Simulator Allen Bradley ControlLogix platform Siemens S7-300 / S7-1200 series Automation Direct 400 series (needed for

EMEC254 – Electromechanical Systems II)

IEC 61131-3 Standard

The International Electrotechnical Commision (IEC) has created a standard, IEC 61131-3 that governs PLC/PAC data types, instructions, structure and programming.

The standard is an attempt to make PLC/PAC manufacturers use the same programming methods in an open type architecture.

Goals & BenefitsIEC 61131-3

PLC/PAC systems are constantly increasing in complexity. Because of this, the goals and benefits of a standard are: to reduce the amount of training for

application programmers. to allow for the easier creation of increasingly

larger programs. the easier implementation of more complex

systems.

PLC/PAC Data Types

The standard defines data types. A data type is a data storage format that

can contain a specific type or range of values. Typical data types are: Boolean (BOOL) Byte Word Integer (INT) Dword (Double Word) And many others…

IEC Data Types

The IEC 61131-3 standard defines the elementary data types as: The types shown in red will be covered in this

course:

Boolean / bit string

Signed integer

Unsigned integer

Floating-point (Real)

Time, duration, date and character string

BOOL INT UINT REAL TIME

BYTE SINT USINT LREAL DATE

WORD DINT UDINT TIME_OF_DAY

DWORD LINT ULINT DATE_AND_TIME

LWORD STRING

Data Types - Storage

Data Type Storage Size

Boolean (BOOL) 1 Bit

Byte 8 Bits

SINT (Single Integer) 8 Bits

Word 16 Bits

Integer (INT) 16 Bits

DINT (Double Integer) 32 Bits

Most likely, Data Types are a foreign language to most students at this point. Therefore, let’s talk about bits, bytes, words, numbers and number systems.