Write Address Detailed Functions
VBLANK
This address controls vertical blank and the latches and
dumping transistors on the input ports by writing into bits
D7, D6 and D1 of the VBLANK register.
D1 [ 1 = start vert. blank, 0 = stop vert. blank]
D6 [ 1 = Enable I4 I5 latches, 0 = disable I4 I5 latches]
D7 [ 1 = dump I6I1I2I3 ports to ground, 0 = remove dump
path to ground]
Note : Disable latches (D6 = 0) also resets latches to
logic true