NAME   rev ADDR type chip Description
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DIWHIGH  p 1E4  W  A D Display window upper bits for start, stop
	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.