WAIT Statement

 Action

 Suspends program execution while monitoring the status of a machine input
 port.

 Syntax


  WAIT  portnumber,  and-expression% ,  xor-expression%


 Remarks

 The  WAIT statement uses the following arguments.

-----------------------------------------------------------------------------
 Argument                                Description
 ----------------------------------------------------------------------------
 Argument                                Description
 ----------------------------------------------------------------------------
  portnumber                             An unsigned integer expression
                                         between 0 and 65,535, inclusive,
                                         that is the number of the machine
                                         input port.

  and-expression%                        An integer expression that is
                                         repeatedly combined with the bit
                                         pattern received at the port,
                                         using an  AND operator; when the
                                         result is nonzero, the  WAIT
                                         statement stops monitoring the
                                         port, and program execution
                                         resumes with the next program
                                         statement.

  xor-expression%                        Can be used to turn bits on and
                                         off in the received bit pattern
                                         before the  AND operation is
                                         applied.
 Argument                                Description
 ----------------------------------------------------------------------------
                                         applied.





 The  WAIT statement is an enhanced version of the  INP function; it suspends
 execution until a specified bit pattern is input from an input port, using
 the following four steps.

   -   1.  The data byte read from the port is combined, using an  XOR
       operation, with

         xor-expression%. If  xor-expression% is omitted, it is assumed to be
        0.

   -   2. The result is combined with  and-expression% using an  AND
       operation.

   -   3. If the result is zero, the first two steps are repeated.

   -   4. If the result is nonzero, execution continues with the next program
       statement.

       It is possible to enter an infinite loop with the  WAIT statement if
       the input port fails to develop a non-zero bit pattern. In this case,
       you must manually restart the machine.

   -   The following example program line illustrates the syntax of the  WAIT
       statement.
 WAIT HandShakePort, 2
 This statement will cause BASIC to do an  AND operation on the bit pattern
 received at the DOS I-O port HandShakePort with the bit pattern represented
 by 2 (00000010).




 Note

 The  WAIT statement is not available in OS-2 protected mode.

 See Also

  INP,  OUT

 Example


 The following example demonstrates the use of the  WAIT statement.

 ' Open and close the port at the proper baud rate.

 OPEN "COM1.9600,N,8,1,BIN" FOR RANDOM AS #1

 CLOSE #1

  PortNum% = &H3F8 'COM1

  NonPrintCharMask% = 96

 ' Wait until there's some activity on COM1.

 ' Mask out characters less than 32 for the first input character.

  LOCATE 12, 15. PRINT "Waiting for a printable input character. "

  WAIT PortNum%, NonPrintCharMask%

 ' Once a printable character comes in, execution continues.

 DO

     'Get a character from the port and evaluate.

     A% = INP(PortNum%)

     SELECT CASE A%

         CASE 7

             Character$ = "   BELL    "

         CASE 8

             Character$ = "BACK SPACE "

         CASE 9

             Character$ = "    TAB    "

         CASE 13

             Character$ = "    CR     "

         CASE 32

             Character$ = "   SPACE   "

         CASE 127

             Character$ = "    DEL    "

         CASE IS < 31, IS > 127

             Character$ = "unprintable"

         CASE ELSE

             Character$ = SPACE$(5) + CHR$(A%) + SPACE$(5)

     END SELECT

     LOCATE 12, 15

     ' Report the input character.

     PRINT "Numeric Value                    ASCII Character"

     LOCATE 14, 20

     PRINT A%; TAB(50); Character$

     IF A% > 127 THEN STOP

     LOCATE 23, 25

     PRINT "Press ANY key to quit."

 LOOP WHILE INKEY$ = ""

 END