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PEN                      Light Pen Status                            Function

 y = PEN(n)

    Returns information about the status of the light pen. For the PEN
    function to be available, a PEN ON statement must first be executed.

           n    A numeric expression in the range 0 to 9; specifies the
                kind of information to be returned. Options are as
                follows:

                0   Returns -1 if light pen has been down since last PEN
                    function; otherwise returns 0.
                1   Returns x coordinate of location where pen was most
                    recently activated.
                2   Returns y coordinate of location where pen was most
                    recently activated.
                3   Returns -1 if pen switch is currently down; otherwise
                    returns 0.
                4   Returns x coordinate of last known valid pen location.
                5   Returns y coordinate of last known valid pen location.
                6   Returns row position of location where pen was most
                    recently activated.
                7   Returns column position of location where pen was most
                    recently activated.
                8   Returns row position of last known valid pen location.
                9   Returns column position of last known valid pen
                    location.