Statement - Suspend the execution of a ST program.

Syntax

   WAIT <BOOL expression> ;

   WAIT_TIME <TIME expression> ;

Remarks

The WAIT statement checks the attached boolean expression and does the following:

- If the expression is TRUE, the program continues normally.

- If the expression is FALSE, then the execution of the program is suspended up to the next PLC cycle. The boolean expression will be checked again during next cycles until it becomes TRUE. The execution of other programs is not affected.

The WAIT_TIME statement suspends the execution of the program for the specified duration. The execution of other programs is not affected.

These instructions are available in ST language only and has no correspondence in other languages. These instructions cannot be called in a User Defined Function Block (UDFB). The use of WAIT or WAIT_TIME in a UDFB provokes a compile error.

WAIT and WAIT_TIME instructions can be called in a sub-program. However, this may lead to some unsafe situation if the same sub program is called from various programs. Re-entrancy is not supported by WAIT and WAIT_TIME instructions. Avoiding this situation is the responsibility of the programmer. The compiler outputs some warning messages if a sub-program containing a WAIT or WAIT_TIME instruction is called from more than one program.

These instructions should not be called from ST parts of SFC programs. This makes no sense as SFC is already a state machine. The use of WAIT or WAIT_TME in SFC or in a sub-program called from SFC provokes a compile error.

These instructions are not available when the code is compiled through a "C" compiler. Using "C" code generation with a program containing a WAIT or WAIT_TIME instruction provokes an error during post-compiling.

These statement are extensions to the standard and are not IEC61131-3 compliant.

ST Language

(* use of WAIT with different kinds of BOOL expressions *)
WAIT BoolVariable;
WAIT (diLevel > 100) AND NOT bAlarm;

WAIT SubProgCall ();

(* use of WAIT_TIME with different kinds of TIME expressions *)
WAIT_TIME t#2s;
WAIT_TIME TimeVariable;

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