Rockwell-automation Logix5000 Controllers Structured Text Programming Instrukcja Użytkownika Pobierz pdf (Strona 31)

Publication 1756-PM007D-EN-P - November 2012 31

Program Structured Text Chapter 1

WHILE…DO

Use the WHILE…DO loop to keep doing something as long as certain

conditions are true.

Operands:

Structured Text

Description: The syntax is:

Operand Type Format Enter

bool_

expression

BOOL Tag

Expression

BOOL tag or expression that evaluates to

a BOOL value

WHILE bool_expression DO

<statement>;

END_WHILE;

IMPORTANT

Make sure that you do not iterate within the loop too many times in a single

scan.

• The controller does not execute any other statements in the routine until

it completes the loop.

• If the time that it takes to complete the loop is greater than the

watchdog timer for the task, a major fault occurs.

• Consider using a different construct, such as IF...THEN.

WHILE bool_expression1 DO

<statement>;

Statements to execute while

bool_expression1 is true

Optional

IF bool_expression2 THEN

EXIT;

If there are conditions when you want to

exit the loop early, use other statements,

such as an IF...THEN construct, to

condition an EXIT statement.

END_IF;

END_WHILE;

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Rockwell-automation Logix5000 Controllers Structured Text Programming Instrukcja Użytkownika Strona 31