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WAIT action


Function
Temporary suspension of the execution of actions.
Declaration
 WAIT expression

 
or
 
WAIT

Parameters
expression in Expressions of BOOL type.

Description
WAIT action with an expression:
Holding the execution of an action till the condition is not met. The condition is met, when a value of the expression is TRUE.

WAIT action without expression:

Holding the execution of actions till the last assignment is executed. This variant of the action WAIT allows to remove time hazards and also check the assignment success. Assignment to a local variable is immediate (synchronously with the execution of actions). On the other hand, assignment to an object (setting an object value) represents only a request and its execution may take a while. There is the possible risk of time hazard.
Example
It assumes the existence of the object U.Int of User variable type, integer value type.
 
; assignment with delay
 U.Int := 1  ; value assignment 
 WAIT  ; waiting for the assignment
 ; if the action WAIT is successful (no error), 
; the value of the object U.Int is certainly 1
 IF U.Int = 1 THEN ; value test
   ; the branch THEN-ELSE is executed whenever the value of the object U.Int is 1 
 ELSE
   ; the branch ELSE-ENDIF won't be never executed
ENDIF
 
U.Int := 2
 ; In this case there is not guaranteed that the value of the object U.Int will be 2 
 ; it depends on the current system load ... 
  IF U.Int = 1 THEN
 ELSE
 ENDIF 

 
The action WAIT allows to test the success of the assignment of a value to an object. For example, writing into an output I/O tag, that is performed via process D2000 KOM.
Example
It assumes the existence of the object M.Cmd of I/O tag type, output integer type.
 
 INT _maxWriteCount = 10 ; maximal count of writings
 INT _writeCount ; writing counter
 
 ON  ERROR WriteFailed ; error handle
 
 _writeCount := 0
 WriteRetry:
   IF _writeCount >= _maxWriteCount GOTO WriteLoopFailed
     _writeCount := _writeCount + 1
     M.Cmd := 1
     WAIT
     ; Successful writing
     END 
 
 ; Writing failed _maxWriteCount-times
  WriteLoopFailed:
   END
 ; unsuccessful writing handle
 WriteFailed:
 GOTO WriteRetry

 
The listed example handles all the error states, that may occur during a writing:
  • process D2000 KOM is not running,
  • station communication failure,
  • writing into a device failed,
  • object is not in the manual mode.

In case of assigning a selection, then this is controlled as the whole. Every fractional writing must be well executed. Such a situation occurs, for the assignment of a value of structure type, if references to objects are in individual items.


Example
Structure definition SD.Rec contains one item of Integer type with the name Int and two items of Object type with the names s Obj1 and Obj2.

The structure type of the object SV.Rec of Structured variable type is SD.Rec and its row number is 2. There are the objects M.1, M.2, M.3, M.4 - output I/O tags of Integer type.


 
RECORD  NOALIAS (SD.Rec) _locArr ; local variable of Structure type
                                 ; disables references to objects 
 REDIM _locArr[2]                ; resizing the array length    
; assignment of values to the local variable of Structure type
_locArr[1]^Int  := 1 
 _locArr[1]^Obj1 := 1 
 _locArr[1]^Obj2 := 2
 _locArr[2]^Int  := 2 
 _locArr[2]^Obj1 := 3
 _locArr[2]^Obj2 := 4
 
; assign references to the objects
 SET SV.Rec[1] ^Obj1 AS M.1
 SET SV.Rec[1] ^Obj2 AS M.2
 SET SV.Rec[2] ^Obj1 AS M.3
 SET SV.Rec[2] ^Obj2 AS M.4
 WAIT  ; execution of the reference change in the system  
 P1:
 SET SV.Rec AS _locArr ; assignment of the whole value
 WAIT 

 
In the example, in the line marked by the label P1, there is performed the assignment of quite 6 values, 4 of which execute assignments to the I/O tags (using the reference to object). The operation success may be verified the following action WAIT. Possible failure of arbitrary assignment will cause the error.

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