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WAIT suspends program execution while monitoring the status of a machine
input port.
 
WAIT  portnumber, and-expression% [,xor-expression%]
 
Usage Notes
    ■ 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:
 
      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 nonzero 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 DOS I/O port HandShakePort with the bit
      pattern represented by 2 (00000010).