Agnus/
                  Read/   Denise/
Register Address  Write   Paula         Function
-------- -------  -----   -------       --------
HBSTOP     1C6      W      A( e ) horizontal line position for hblank stop
HBSTRT     1C4      W      A( e ) horizontal line position for hblank start
HCENTER    1E2      W      A( e ) horizontal position for vsync on interlace
HSSTOP     1C2      W      A( e ) horizontal line position for hsync stop
HSSTRT     1DE      W      A( e ) horizontal sync start (varhsy)
HTOTAL     1C0      W      A( e ) highest number count, horiz. line
                                     (VARBEAMEN=1)