Agnus/
                  Read/   Denise/
Register Address  Write   Paula         Function
-------- -------  -----   -------       --------
VSSTOP     1CA      W      A( E ) Vertical line position for VSYNC stop
VSSTRT     1E0      W      A( E ) Vertical sync start   (VARVSY)
VTOTAL     1C8      W      A( E ) Highest numbered vertical line
                                      (VARBEAMEN=1)