Rockwell Automation Logix5000 Controllers Structured Text Programming Manual - Manual (Page 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
No
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;