IEC 61131-3

• Ladder diagram, graphical
• Function block diagram, graphical
• Structured text, textual
• Instruction list, textual deprecated. Per IEC 61131-3-2025, chapter 7.2 Instruction List is no longer included in Edition 4. Thus, IL is no longer part of IEC 61131-3.
• Sequential function chart, has elements to organize programs for sequential and parallel control processing, graphical.

Data types

Elementary Data Types (basic)

• Bit Strings – groups of on/off values
• * BOOL - 1 bit
• * BYTE – 8 bit
• * WORD – 16 bit
• * DWORD – 32 bit
• * LWORD – 64 bit
• INTEGER – whole numbers
• * SINT – signed short integer
• * INT – signed integer
• * DINT – signed double integer
• * LINT – signed long integer
• * USINT – Unsigned short integer
• * UINT – Unsigned integer
• * UDINT – Unsigned double integer
• * ULINT – Unsigned long integer
• REAL – floating point IEC 60559
• * REAL –
• * LREAL –

Elementary Data Types (Date and Time)

• Duration
• * TIME –. Literals in the form of T#5m90s15ms
• * LTIME –. Literals extend to nanoseconds in the form of T#5m90s15ms542us15ns
• Date
• * DATE – calendar date
• * LDATE – calendar date
• Time of day
• * TIME_OF_DAY / TOD – clock time
• * LTIME_OF_DAY / LTOD – clock time
• Date and time of Day
• * DATE_AND_TIME / DT – time and date
• * LDATE_AND_TIME / LDT – time and date

Elementary Data Types (Character / Character string)

• Existing
• * CHAR – Single-byte character
• * WCHAR – Double-byte character
• * STRING – Variable-length single-byte character string. Literals specified with single quote, 'This is a STRING Literal'
• * WSTRING – Variable-length double-byte character string. Literals specified with a double quote, "This is a WSTRING Literal"
• New in version 4 of the standard
• * UCHAR – Single character encoded according to UTF-8
• * USTRING - Variable-length character string in which each character is encoded according to UTF-8

Generic Data Types

• ANY
• ANY_DERIVED
• ANY_ELEMENTARY
• * ANY_MAGNITUDE
• ** ANY_NUM
• *** ANY_REAL: LREAL, REAL
• *** ANY_INT
• **** ANY_UNSIGNED: ULINT, UDINT, UINT, USINT
• **** ANY_SIGNED: LINT, DINT, INT, SINT
• ** ANY_DURATION: TIME, LTIME
• * ANY_BIT: LWORD, DWORD, WORD, BYTE, BOOL
• * ANY_CHARS
• ** ANY_STRING: STRING, WSTRING
• ** ANY_CHAR: CHAR, WCHAR
• * ANY_DATE: DATE_AND_TIME, DATE_AND_TIME, DATE, TIME_OF_DAY, LTIME_OF_DAY

User-defined Data Types

• Enumerated data type
• Enumerated data type with named value
• Subrange data type – puts limits on value i.e., INT for current
• Array data type – multiple values stored in the same variable.
• Structured data type – composite of several variables and types.
• Directly derived data type – type derived from one of the above types to give new name and initial value as a type.
• References – a kind of strongly typed pointer. Arithmetic operation of the value of this type is prohibited.

Variables

• Global
• Direct
• I/O Mapping – Input, Output, I/O
• External
• Temporary

Configuration

• Resource – Like a CPU
• Tasks – Can be multiple per CPU.
• Programs – Can be executed once, on a timer, on an event.

Program organization unit (POU)

• Functions
• * Standard: ADD, SQRT, SIN, COS, GT, MIN, MAX, AND, OR, etc.
• * Custom
• Function Blocks
• * Standard:
• * Custom – Libraries of functions can be supplied by a vendor or third party.
• Programs

Configuration, resources, tasks

• Configuration – processing resources, memory for IO, execution rates, number of tasks.

Object oriented programming (OOP)

• The 3rd revision of the standard describes how to implement OOP within the application programming