Rockwell-automation Logix5000 Controllers Structured Text Programming Manual do Utilizador descarregar pdf (Página 22)

22 Publication 1756-PM007D-EN-P - November 2012

Chapter 1 Program Structured Text

IF...THEN

Use IF…THEN to do something if or when specific conditions occur.

Operands:

Structured Text

Description:

The syntax is:

To use ELSIF or ELSE, follow these guidelines.

1. To select from several possible groups of statements, add one or more

ELSIF statements.

• Each ELSIF represents an alternative path.

• Specify as many ELSIF paths as you need.

• The controller executes the first true IF or ELSIF and skips the rest

of the ELSIFs and the ELSE.

2. To do something when all of the IF or ELSIF conditions are false, add

an ELSE statement.

Operand Type Format Enter

bool_

expression

BOOL Tag

Expression

BOOL tag or expression that evaluates to

a BOOL value (BOOL expression)

IF bool_expression THEN

<statement>;

END_IF;

IF bool_expression1 THEN

<statement >;

Statements to execute when

bool_expression1 is true

Optional

ELSIF bool_expression2 THEN

<statement>;

Statements to execute when

bool_expression2 is true

Optional

ELSE

<statement>;

Statements to execute when

both expressions are false

END_IF;

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Rockwell-automation Logix5000 Controllers Structured Text Programming Manual do Utilizador Página 22