5.
Define
Modulo.
Set registers BPLIMOD and BPL2MOD. Set modulo to 0 for
non-interlaced, 40 for interlaced.
6.
Write
Copper
Instructions
To
Handle
Redisplay.
7.
Enable
Color
Display.
Set
bit
9
in
BPLCONO
to
enable the color display
on
a
composite video monitor. RGB video is not affected.
EXAMPLES
OF
FORMING
BASIC
PLAYFIELDS
The
following examples show how
to
set the registers and write the coprocessor lists for
two different play fields.
The
first example sets up a 320 x 200 playfield with one bit-plane, which is located
at
$21000. Also, a Copper list is set up
at
$20000.
CUSTOM
BPLCONO
BPLCONI
BPLCON2
BPLIMOD
DDFSTRT
DDFSTOP
DIWSTRT
DIWSTOP
VPOSR
COLOROO
COLOROI
COLOR02
COLOR03
DMACON
COPILCH
LEA
MOVE.W
MOVE.W
MOVE.W
MOVE.W
MOVE.W
MOVE.W
MOVE.W
MOVE.W
MOVE.W
EQU
$DFFOOO
EQU $100
EQU $102
EQU $104
EQU $108
EQU $092
EQU $094
EQU $08E
EQU $090
EQU $004
EQU $180
EQU $182
EQU $184
EQU $186
EQU $096
EQU $080
CUSTOM,AO
#$1200,BPLCONO(AO)
#O,BPLCONl(AO)
#O,BPLIMOD(AO)
#$0038,DDFSTRT(AO)
#$OODO,DDFSTOP(AO)
#$2C81,DIWSTRT(AO)
#$F4Cl,DIWSTOP(AO)
#$OFOO,
COLOROO(AO)
#$OFFO,COLOROl(AO)
; Copper location register 1
; (high three bits)
;AO
points at custom chips
; One bit-plane, enable composite color
;Set horizontal scroll value to 0
;Set modulo to 0 for all odd btt-planes
;Set data-fetch start to $38
;Set data-fetch stop to
$DO
;Set
DIWSTRT
to $2C81
;Set
DIWSTOP
to $F4C1
;Set background color to red
;Set color register
1 to yellow
Playfield Hardware
55
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