Structured Text (ST), a programming language used in
Programmable Logic Controllers (PLCs).
Structured Text is a high-level language that's widely used in industrial
automation and control systems. It's a text-based language that allows
programmers to write logic and control code for PLCs, which are used in
various industries such as manufacturing, oil and gas, water treatment,
and more.
ST is known for its ease of use, flexibility, and readability, making it a
popular choice among PLC programmers.
What is Structured Text (ST)?
Structured Text (ST) is a high-level programming language used to program
Programmable Logic Controllers (PLCs). It's a text-based language that
allows you to write logic and control code for PLCs.
Key Features of ST:
- Easy to Read: ST code is written in plain English, making it easy
to understand and maintain. - High-Level Language: ST is a high-level language, meaning it
abstracts away from the low-level details of the hardware, allowing you to
focus on the logic of your program. - Platform Independent: ST code can be run on any PLC that supports
the language, regardless of the manufacturer or model.
Basic Syntax:
Here's a simple example of an ST program:
PROGRAM Example
VAR
Input : BOOL;
END_VAR
IF Input THEN
Output := TRUE;
ELSE
Output := FALSE;
END_IF
Let me explain what each part does:
PROGRAM
is the keyword that starts a new program.Example
is the name of our program.VAR
declares variables, which are stored values used in our program.
In this case, we have two variables:Input
andOutput
.- The
IF
statement checks a condition (in this case, whetherInput
is
TRUE or FALSE). - If the condition is true, then the code inside the
THEN
block is
executed. - If the condition is false, then the code inside the
ELSE
block is
executed.
Basic Data Types:
ST uses various data types to store values. Here are some common ones:
- BOOL: A boolean value that can be TRUE or FALSE.
- WORD: A 16-bit unsigned integer value.
- DWORD: A 32-bit unsigned integer value.
- REAL: A floating-point number with a maximum of 8 decimal places.
Control Statements:
ST supports various control statements, such as:
- IF-THEN-ELSE: Used to execute different code based on conditions.
- FOR: Used for looping through a range of values.
- WHILE: Used for looping until a condition is met.
- CASE: Used for executing different code based on the value of an
expression.
That's a basic introduction to Structured Text (ST) and its syntax! Do you
have any specific questions or topics you'd like me to cover next?
teach me more
Let's dive deeper into Structured Text (ST) programming.
Variables and Data Types
In ST, variables are declared using the VAR
keyword. Here are some
examples:
VAR
Input : BOOL; // boolean variable
Counter : WORD := 0; // 16-bit unsigned integer variable with initial
value 0
Temperature : REAL := 20.5; // floating-point number variable with
initial value 20.5
END_VAR
ST supports various data types, including:
- BOOL: A boolean value that can be TRUE or FALSE.
- WORD: A 16-bit unsigned integer value (0-65535).
- DWORD: A 32-bit unsigned integer value (0-4294967295).
- REAL: A floating-point number with a maximum of 8 decimal places
(-3.40E38 to 3.40E38). - TIME: A time value in hours, minutes, and seconds.
Operators
ST supports various operators for performing arithmetic, comparison,
logical, and assignment operations:
- Arithmetic Operators:
+
(addition)-
(subtraction)*
(multiplication)/
(division)MOD
(modulo operation)
- Comparison Operators:
=
(equal to)<>
(not equal to)<
(less than)>
(greater than)<=
(less than or equal to)>=
(greater than or equal to)
- Logical Operators:
AND
(logical AND)OR
(logical OR)NOT
(logical NOT)
Control Statements
ST supports various control statements for executing different code:
- IF-THEN-ELSE:
IF Input THEN
Output := TRUE;
ELSE
Output := FALSE;
END_IF
- FOR:
FOR Counter := 0 TO 10 DO
LED := TRUE;
END_FOR
- WHILE:
VAR
Counter : WORD := 0;
END_VAR
WHILE Counter < 5 DO
LED := TRUE;
Counter := Counter + 1;
END_WHILE
- CASE:
CASE Input OF
FALSE:
Output := FALSE;
TRUE:
Output := TRUE;
END_CASE
Functions
ST supports user-defined functions for reusing code:
FUNCTION Add(a : WORD; b : WORD) : WORD
VAR
Result : WORD;
END_VAR
Result := a + b;
RETURN Result;
END_FUNCTION
You can call the Add
function using:
Output := Add(10, 20);
Arrays and Structures
ST supports arrays and structures for storing multiple values:
- Arrays:
VAR
Array : ARRAY[0..9] OF WORD;
END_VAR
Array[5] := 50;
- Structures:
TYPE
Point : STRUCT
X : WORD;
Y : WORD;
END_STRUCT
END_TYPE
Point.X := 10;
Point.Y := 20;
These are some of the basic features and constructs in Structured Text
(ST). Do you have any specific questions or topics you'd like me to cover
next?
Loops
ST supports various types of loops for executing code repeatedly:
- FOR Loops:
FOR i := 0 TO 9 DO
Output[i] := TRUE;
END_FOR
- WHILE Loops:
VAR
i : WORD := 0;
END_VAR
WHILE i < 10 DO
Output[i] := TRUE;
i := i + 1;
END_WHILE
- DO-UNTIL Loops:
VAR
i : WORD := 0;
END_VAR
DO
Output[i] := TRUE;
i := i + 1;
UNTIL i >= 10
Arrays
ST supports arrays for storing multiple values:
TYPE
MyArray : ARRAY[0..9] OF WORD;
END_TYPE
You can initialize an array using:
MyArray := [0, 20, 30, 40, 50, 60, 70, 80, 90, 100];
Or you can access individual elements of the array using:
Output := MyArray[5]; // Output will be 50
Structures
ST supports structures for storing multiple values:
TYPE
Point : STRUCT
X : WORD;
Y : WORD;
END_STRUCT
END_TYPE
MyPoint : POINT;
You can initialize a structure using:
MyPoint := [X:=10, Y:=20];
Or you can access individual elements of the structure using:
Output := MyPoint.X; // Output will be 10
Records
ST supports records for storing multiple values:
TYPE
Point : RECORD
X : WORD;
Y : WORD;
END_RECORD
END_TYPE
MyPoint : POINT;
You can initialize a record using:
MyPoint := [X:=10, Y:=20];
Or you can access individual elements of the record using:
Output := MyPoint.X; // Output will be 10
Functions
ST supports user-defined functions for reusing code:
FUNCTION Add(a : WORD; b : WORD) : WORD
VAR
Result : WORD;
END_VAR
Result := a + b;
RETURN Result;
END_FUNCTION
You can call the Add
function using:
Output := Add(10, 20); // Output will be 30
Subroutines
ST supports subroutines for executing code:
SUBROUTINE MySub
VAR
i : WORD;
END_VAR
FOR i := 0 TO 9 DO
Output[i] := TRUE;
END_FOR
END_SUBROUTINE
You can call the MySub
subroutine using:
MySub();
Type Definitions
ST supports type definitions for creating new data types:
TYPE
MyType : TYPE DEFINITION OF WORD;
END_TYPE
You can use the MyType
type in your code like any other built-in type.
Library Functions
ST supports library functions for accessing pre-defined functions and
variables:
VAR
i : WORD := Lib_Add(10, 20);
END_VAR
You can use library functions to access pre-defined functions and
variables.
Object-Oriented Programming
ST supports object-oriented programming (OOP) concepts such as classes,
objects, inheritance, and polymorphism:
- Classes:
CLASS MyClass
VAR
X : WORD;
END_VAR
CONSTRUCTOR MyClass
VAR
i : WORD := 0;
END_VAR
X := i;
END_CONSTRUCTOR
- Objects:
VAR
myObject : MyClass;
END_VAR
myObject := new();
- Inheritance:
CLASS MySubClass : MyClass
VAR
Y : WORD;
END_VAR
CONSTRUCTOR MySubClass
VAR
i : WORD := 0;
END_VAR
Y := i;
END_CONSTRUCTOR
- Polymorphism:
FUNCTION MyFunction(obj : OBJECT)
VAR
result : WORD;
END_VAR
CASE obj OF
MyClass :
result := MySubClass.X;
MySubClass :
result := MySubClass.Y;
END_CASE
RETURN result;
END_FUNCTION
Event-Driven Programming
ST supports event-driven programming (EDP) concepts such as events,
handlers, and publishers:
- Events:
EVENT MyEvent
VAR
data : WORD;
END_VAR
- Handlers:
ON_EVENT(MyEvent)
VAR
i : WORD := 0;
END_VAR
data := i;
END_ON_EVENT
- Publishers:
PUBLISH(MyEvent, 10);
Graphical User Interface
ST supports graphical user interface (GUI) programming concepts such as
windows, buttons, labels, and text boxes:
- Windows:
WINDOW MyWindow
VAR
width : WORD := 400;
END_VAR
CREATE(MyWindow, width, 300);
- Buttons:
BUTTON MyButton
VAR
text : STRING := "Click me!";
END_VAR
CREATE(MyButton, 100, 50);
- Labels:
LABEL MyLabel
VAR
text : STRING := "Hello, world!";
END_VAR
CREATE(MyLabel, 150, 20);
- Text boxes:
TEXT_BOX MyTextBox
VAR
width : WORD := 200;
END_VAR
CREATE(MyTextBox, width, 50);
**Networking^[[200~```st
TYPE
Point : RECORD
X : WORD;
Y : WORD;
END_RECORD
END_TYPE
MyPoint : POINT;
You can initialize a record using:
```st
MyPoint := [X:=10, Y:=20];
Or you can access individual elements of the record using:
Output := MyPoint.X; // Output will be 10
Functions
ST supports user-defined functions for reusing code:
^[[201~**
ST supports networking programming concepts such as sockets, clients, and
servers:
- Sockets:
SOCKET MySocket
VAR
port : WORD := 8080;
END_VAR
CREATE(MySocket, port);
- Clients:
CLIENT MyClient
VAR
server : STRING := "localhost";
END_VAR
CONNECT(MyClient, server, 8080);
- Servers:
SERVER MyServer
VAR
port : WORD := 8080;
END_VAR
LISTEN(MyServer, port);
Database
ST supports database programming concepts such as connections, queries,
and transactions:
- Connections:
DATABASE MyDatabase
VAR
host : STRING := "localhost";
END_VAR
CONNECT(MyDatabase, host);
- Queries:
QUERY MyQuery
VAR
query : STRING := "SELECT * FROM users;";
END_VAR
EXECUTE(MyQuery, query);
- Transactions:
TRANSACTION MyTransaction
VAR
transaction : BOOL := TRUE;
END_VAR
BEGIN(MyTransaction);
...
COMMIT(MyTransaction);
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标签:WORD,Text,Structured,ST,Output,VAR,END,supports From: https://www.cnblogs.com/PrepAndPonder/p/18516692