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README.md

CODESYS (IEC 61131-3) for Beginners - Part 1

Table of Contents

Introduction

CODESYS is a development environment for programming controller applications in line with the IEC 61131-3 standard.

IEC 61131-3 defines three graphical and two textual programming language standards

  • IL (Instruction List, text) is an assembler like programming language (Is now deprecated but available for backward compatibility)
  • ST (Structured Text, text) is similar to programming in Pascal or C
  • LD (Ladder Diagram, graphic) enables the programmer to virtually combine relay contacts and coils
  • FBD (Function Block Diagram, graphic) enables the user to rapidly program both Boolean and analogue expressions
  • SFC (Sequential Function Chart, graphic) is convenient for programming sequential processes and flows

Additional graphical editor available in CODESYS not defined in the IEC standard: CFC (Continuous Function Chart, graphical) is a sort of freehand FBD editor. Other than in the network-oriented FBD editor where the connections between inputs, operators and outputs are set automatically they have to be drawn by the programmer. All boxes can be placed freely which makes it possible to program feedback loops without interim variables.

Data Type

Integer

Data type Description Minimum value Maximum value Memory size
SINT Signed Short Integer -128 127 1 byte
INT Signed Integer -32768 32767 2 bytes
DINT Signed Double Integer -2147483648 2147483647 4 bytes
LINT Signed Long Integer -263 263-1 8 bytes
USINT Unsigned Short Integer 0 255 1 byte
UINT Unsigned Integer 0 65535 2 bytes
UDINT Unsigned Double Integer 0 4294967295 4 bytes
ULINT Unsigned Long Integer 0 264-1 8 bytes

Real (Floating-point)

Data type Description Minimum value Maximum value Memory size
REAL Real (Float) -3.402823e+38 3.402823e+38 4 bytes
LREAL Long Real (Double) -1.7976931348623158e+308 1.7976931348623158e+308 8 bytes

Character / Character string

Data type Description Memory size
CHAR Single character 1 byte
WCHAR Single character 2 bytes
STRING Variable-length character Variable-length single-byte character
WSTRING Variable-length character Variable-length single-byte character

Bit string

Data type Description Memory size
BYTE 8 bit binary 1 byte
WORD 16 bit binary 2 bytes
DWORD 32 bit binary 4 bytes
LWORD 64 bit binary 8 bytes

Boolean

Data type Description Memory size
BOOL 0/FALSE 1 bit

Date/Time

Data type Description Initial value
TIME Duration T#0s
LTIME Duration LTIME#0s
DATE Calendar date –
LDATE Calendar date LDATE#1970‐01‐01
TIME_OF_DAY or TOD Time of day TOD#00:00:00
DATE_AND_TIME or DT Date and time of day –

Identifiers

Rules of naming identifiers

  • Motor, motor, and mOtOr are refered as same identifier.
  • Begin with a letter or an _ (underscore).
  • Numbers are allowed. But cannot put in first character.
  • Cannot contain a space.
  • Cannot end with an underscore or have two underscores.

Example of correct Identifiers

  • MoTor
  • _Motor
  • Mo_tor
  • Motor_lvl2_3

Example of incorrect identifiers

  • motor__1 (two underscores)
  • 1_motor (numbers first)
  • Motor 1 (space)
  • Motor_ (ends with underscore)

Literals

Integer Literals

Decimal Binary Octal Hexadecimal
0 2#00000000 8#000 16#00
38 2#0010_0110‬ 8#046 16#26
-17 -2#0001_0001 or
2#1110_1111		 −8#21 or
8#357		 -16#11 or
16#EF

Time Literals

Date/Time Description
d days
h hours
m minutes
s seconds
ms milliseconds

Example Time Literals

  • T*#30s
  • T#‐25s (negative time)
  • T#12.4ms
  • t#12h
  • T#12h23m42s
  • t#12h_23m_42s_67ms

Date/Time Literals

The literal should follow the form:

  • DATE or D # Year ‐ Month no. ‐ Day no.

  • TIME_OF_DAY (TOD):
    TIME_OF_DAY or TOD # Hours : Minutes : Seconds (Note that hours, minutes, and seconds are separated by a colon, while year, month, and day
    are separated by a hyphen.)

  • DATE_AND_TIME (DT):
    DATE_AND_TIME or DT # DATE‐literal ‐ TOD‐literal

Example Date/Time Literals

  • DATE#2020‐09‐30
  • D#1987‐11‐17
  • time_of_day#14:25:00
  • TOD#17:30:45
  • DATE_AND_TIME#2020‐10‐02‐13:45:00
  • dt#2020‐05‐09‐17:08:00

Character string Literal

Single quote ' is used for CHAR and STRING.
Double quotes " is used for WCHAR and WSTRING.

Example Character string Literal

aString := 'This is a STRING'
aWString := "This is a WSTRING"

Variables

Types Description
VAR Local variables
VAR_GLOBAL Global variables outside of POU*
VAR_INPUT Pass variables into POU*
VAR_OUTPUT Return variables from POU*
VAR_IN_OUT Pass and return variables from POU*
VAR_EXTERNAL Access Global variables from POU*
VAR_STAT Static variables
VAR_TEMP Variables deleted after POU* exit
VAR_INST Only for methods of a function block
VAR_CONFIG I/O addresses
VAR_ACCESS Direct access to hardware variables

* POU - Program Organization Unit

Variables Syntax

VAR_TYPE
  VAR NAME : ARRAY [lower..upper] OF DATATYPE;
  VAR NAME : ARRAY [lower1..upper1, lower2..upper2] OF DATATYPE;
END_VAR_TYPE

Example Variables

VAR
  xJsonParseTrigger : BOOL := TRUE;
END_VAR

VAR_INPUT
  udiSizeData : UDINT;
  sPointer : STRING(255);
END_VAR

VAR_OUTPUT
  xBusy : BOOL;
  xError : BOOL;
  sStatus : STRING;
END_VAR

Constants and Retain

VAR CONSTANT
  Setpoint : INT := 75;
END_VAR
VAR RETAIN
  Setpoint : INT := 75;
END_VAR

Array

Array Syntax

TYPE
  Tab_1dim : ARRAY [lower..upper] OF DATATYPE;
  Tab_2dim : ARRAY [lower1..upper1, lower2..upper2] OF DATATYPE;
END_TYPE

Example defining Array Data Types

VAR
  One_dim: ARRAY [0..9] OF USINT;
  Two_dim: ARRAY [1..2, 1..5] OF INT;
  Three_dim: ARRAY [0..3, 0..3, 0..3] OF REAL;
END_VAR

Data Structure

Declared with the following syntax :

TYPE Name_of_datatype:
  STRUCT
    <Declaration of datatype 1>;
    <Declaration of datatype 2>;
    <Declaration of datatype n>;
  END_STRUCT
END_TYPE

Example declaration of Data Structure

TYPE MOTOR_SIGNAL:
    STRUCT
        Raw_value : WORD;
        Scaled_value : REAL;
        Min_raw : INT (‐32767..0);
        Max_raw : UINT (0..32768)
    END_STRUCT
END_TYPE

Data Type Conversion

Example From Boolean to Other Data Types

B := BOOL_TO_INT(TRUE); (* Result: 1 *)
O := BOOL_TO_STRING(TRUE); (* Result: 'TRUE' *)
RI := BOOL_TO_TIME(TRUE); (* Result: T#1ms *)
N := BOOL_TO_TOD(TRUE); (* Result: TOD#00:00:00.001 *)
G := BOOL_TO_DATE(FALSE); (* Result: D#1970‐01‐01 *)

Example From Floating‐Point to Other Data Types

J := REAL_TO_INT(7.5); (* Result: J = 8 *)
A := REAL_TO_INT(7.4); (* Result: A = 7 *)
C := REAL_TO_INT(−7.5); (* Result: C = −8 *)
K := REAL_TO_STRING(35.27) (* Result: K = '35.27' *)

B := TRUNC_INT(−23.6) (* Result: B = −23 *)
B := REAL_TO_INT(−23.6) (* Result: B = −24 *)