Rockwell-automation Logix5000 Controllers Structured Text Programming Manual do Utilizador descarregar pdf (Página 34)

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

Chapter 1 Program Structured Text

REPEAT…UNTIL

Use the REPEAT…UNTIL loop to keep doing something until 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 (BOOL expression)

REPEAT

<statement>;

UNTIL bool_expression

END_REPEAT;

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.

REPEAT

<statement>;

Statements to execute while

bool_expression1 is false

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;

UNTIL bool_expression1

END_REPEAT;

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Rockwell-automation Logix5000 Controllers Structured Text Programming Manual do Utilizador Página 34