VLOOP: MOVE.W
VLl:
AND.W
BEQ
MOVE.W
MOVE.W
BPL
MOVE.L
BRA
MOVE.L
BRA
; Character list
INTREQR(AO),DO
#$0020,DO
VLOOP
#$0020,INTREQ(AO)
VPOSR(AO),DO
VLl
#$20000,BPLIPTH(AO)
VLOOP
#$20050,BPLIPTH(AO)
VLOOP
;Read interrupt requests
jMask
off
all but vertical blank
jLoop until vertical blank comes
jReset vertical interrupt
jRead
LOF
bit into
DO
bit
15
jlf
LOF
=
0,
jump
;LOF = 1, point to $20000
;Back to top
;LOF =
0,
point
to
$20050
;Back to top
DC.L $18FC3DFO,$3C6666D8,$3C66COCC,$667CCOCC
DC.L
$7E66COCC,$C36666D8,$C3FC3DFO,$OOOOOOOO
DC.L
$FFFFFFFF
Forming
a
Dual-playfield
Display
For
more flexibility
in
designing your background display, you can specify two playfields
instead of one. In dual-playfield mode, one play
field
is
displayed directly
in
front of the
other. For example, a computer game display might have some action going on in one
playfield in the background, while the other playfield is showing a control panel
in
the
foreground. You can then change either the foreground or the background without hav-
ing
to
redesign the entire display. You can also move the two playfields independently.
A dual-playfield display
is
similar to a single-playfield display, differing only
in
these
aspects:
o Each play
field
in a dual display is formed from one, two or three bit-planes.
o
The
colors in each playfield (up to seven plus transparent) are taken from
different sets of color registers.
o You must set a bit
to
activate dual-playfield mode.
58 Play
field
Hardware
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