Rockwell-automation Logix5000 Controllers Structured Text Programming Manual de usuario descargar pdf (Pagina 32)

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

Chapter 1 Program Structured Text

These diagrams show how a WHILE...DO loop executes and how an EXIT

statement leaves the loop early.

Arithmetic Status Flags: Not affected

Fault Conditions:

Example 1:

While the bool_expression is true, the controller

executes only the statements within the

WHILE…DO loop.

To stop the loop before the conditions are true, use an

EXIT statement.

Statement 1

Statement 2

Statement 3

BOOL expression

True

False

Rest of the routine

Yes

Statement 1

Statement 2

Statement 3

BOOL expression

True

False

Rest of the routine

A major fault will occur if Fault type Fault code

The construct loops too long 6 1

If you want this Enter this structured text

The WHILE...DO loop evaluates its conditions first. If the

conditions are true, the controller then executes the

statements within the loop.

This differs from the REPEAT...UNTIL loop because the

REPEAT...UNTIL loop executes the statements in the construct

and then determines if the conditions are true before

executing the statements again. The statements in a

REPEAT...UNTIL loop are always executed at least once. The

statements in a WHILE...DO loop might never be executed.

pos := 0;

While ((pos <= 100) & structarray[pos].value <> targetvalue)) do

pos := pos + 2;

String_tag.DATA[pos] := SINT_array[pos];

end_while;

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