An introduction to PLC/PAC programming

1. Chapter 03
Introduction to Chapter 03

2. 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

3. 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 ControlLogix/CompactLogix platforms
 Siemens S7-300 / S7-1200 series
 Allen Bradley Creative Components Workbench
(CCW), using the AB Micro 800 series PLCs
 Allen Bradley SLC500/MicroLogix information is
provided but not covered in class

4. IEC 61131-3 Standard
 The International Electrotechnical
Commission (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.

5. Goals & Benefits
IEC 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.
 a less steep learning curve for maintenance
technicians who have service more than one
brand of PLC/PAC.

6. 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…

7. 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

8. 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, later in this
course we will talk about bits, bytes, words,
numbers and number systems.