REPEAT_UNTIL

Use the REPEAT_UNTIL loop to continue performing an action until conditions are true.

Operands

REPEAT

<statement>;

Structured Text

Operand	Type	Format	Enter
bool_ expression	BOOL	Tag expression	BOOL tag or expression that evaluates to a BOOL value (BOOL expression)

IMPORTANT:

Do not iterate within the loop too many times in a single scan.

The controller does not execute other statements in the routine until it completes the loop.

A major fault occurs when completing the loop takes longer than the watchdog timer for the task.

Consider using a different construct, such as IF_THEN.

Description

The syntax is:

The following diagrams show how a REPEAT_UNTIL loop executes and how an EXIT statement leaves the loop early.

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.

Affects Math Status Flags

Fault Conditions

A major fault will occur if	Fault type	Fault code
The construct loops too long	6	1

Example 1

If performing the following,	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;

Example 2

If performing the following,	Enter this structured text
Move ASCII characters from a SINT array into a string tag. (In a SINT array, each element holds one character.) Stop when you reach the carriage return. Initialize Element_number to 0. Count the number of elements in SINT_array (array that contains the ASCII characters) and store the result in SINT_array_size (DINT tag). Set String_tag[element_number] = the character at SINT_array[element_number]. Add 1 to element_number. This lets the controller check the next character in SINT_array. Set the Length member of String_tag = element_number. (This records the number of characters in String_tag so far.) If element_number = SINT_array_size, then stop. (You are at the end of the array and it does not contain a carriage return.) If the character at SINT_array[element_number] = 13 (decimal value of the carriage return), then stop.	element_number := 0;
	SIZE(SINT_array, 0, SINT_array_size);
	Repeat
	String_tag.DATA[element_number] := SINT_array[element_number];
	element_number := element_number + 1;
	String_tag.LEN := element_number;
	If element_number = SINT_array_size then
	exit;
	end_if;
	Until SINT_array[element_number] = 13
	end_repeat;

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