DIWHIGH

         This is an added register for Hires chips, and allows
         larger start & stop ranges. If it is not written, the above
         (DIWSTRT, STOP) description holds. If
         this register is written, direct start & stop positions
         anywhere on the screen. It doesn`t affect the UHRES pointers.


         BIT# 15  14  13  12  11  10  09  08  07  06  05  04  03  02  01  00
               X   X  H10 H1  H0  V10 V9  V8   X   X  H10 H1  H0  V10 V9  V8
                      (stop)                 |         (start)


         Take care (X) bits should always be written to 0 to
         maintain upwards compatibility. H1 and H0 values define
         70ns amd 35ns increments respectively, and new LISA bits.


   Note: In all 3 display window registers, horizontal bit
         positions have been renamed to reflect HIRES pixel
         increments, e.g. what used to be called H0 is now
         referred to as H2.