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.
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