Rockwell-automation Logix5000 Controllers Structured Text Programming Manuale Utente Scaricare il pdf (Pagina 35)

Publication 1756-PM007D-EN-P - November 2012 35

Program Structured Text Chapter 1

These diagrams show how a REPEAT...UNTIL 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 false, the controller

executes only the statements within the

REPEAT…UNTIL loop.

To stop the loop before the conditions are false, use

an EXIT statement.

Statement 1

Statement 2

Statement 3

BOOL expression

False

True

Rest of the routine

BOOL expression

False

True

Rest of the routine

Statement 1

Statement 2

Statement 3

Yes

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 REPEAT...UNTIL loop executes the statements in the

construct and then determines if the conditions are true before

executing the statements again.

This differs from the WHILE...DO loop because the WHILE...DO

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

conditions are true, the controller then executes the

statements within the loop. 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 := -1;

REPEAT

pos := pos + 2;

UNTIL ((pos = 101) OR (structarray[pos].value = targetvalue))

end_repeat;

1 2 ... 30 31 32 33 34 35 36 37 38 39 40

Commenti su questo manuale

Nessun commento

Rockwell-automation Logix5000 Controllers Structured Text Programming Manuale Utente Pagina 35

Commenti su questo manuale

Prodotti e manuali riguardandi Apparecchiature Rockwell-automation Logix5000 Controllers Structured Text Programming