Changes
The decoder outputs some control signals and an 8bit luminance signal. That data can't be squeezed through the 8bit input port, so some of the luminance bits are left unconnected (the CPC's color palette couldn't display them anyways).
== Source Code ==
io_port equ 0F8F0h
temp equ 40000
lum equ 40001
xreg equ 40002
yreg equ 40004
hxreg equ 40006
blkadd equ 40008
org 0A028h ;=41000 decimal
entrypoint:
ld a,00h
ld [hxreg+1],a
call 0BC0Eh ;SCR_SET_MODE
rerun:
ld hl,160-1
ld [xreg],hl
ld hl,200-1
ld [yreg],hl
ld ix,bytead+15 ;\
ld a,0fh ;ink index ;
ld [temp],a ;ink index ;
colset: ;
ld a,[ix] ;ink address ;
ld b,a ; init ink 0..15
ld c,a ;
ld a,[temp] ;ink index ;
call 0BC32h ;SCR_SET_INK ;
ld hl,temp ;ink index ;
dec [hl] ;ink index ;
jp m,wtfrm ;lop done ;
dec ix ;ink address ;
jp colset ;lop next ;/
wtfrm:
call 0BD19h ;MC_WAIT_FLYBACK
call 0BD19h ;MC_WAIT_FLYBACK
loop1:
di
ld bc,io_port
line: ;\
in a,[bc] ;[port] ;
bit 6,a ;[port].bit6 ;
jr z,line ;/
enline: ;\
in a,[bc] ;[port] ;
bit 6,a ;[port].bit6 ;
jr nz,enline ;/
ld d,0Ah ;\
delay: ; delay
dec d ;
jr nz,delay ;/
loop2:
di
ld d,2
ld bc,io_port
smpl: ;\
in a,[bc] ;[port] ;
bit 7,a ;[port].bit7 ;
jr nz,smpl ;/
ensmpl: ;\
in a,[bc] ;[port] ;
bit 7,a ;[port].bit7 ;
jr z,ensmpl ;/
dec d
jr nz,smpl
getlum:
in a,[bc] ;[port] ;\
and a,0fh ;[port].bit0-3 ;
ld [lum],a ;/
rra ;\
rr b ;
rra ;
rr b ;
rra ;
rr c ;
rra ;
rr b ;
ld d,0 ;
rlc b ;
rr d ;
rr d ;
rlc b ;
rr d ;
rr d ;
rlc c ;
rr d ;
rr d ;
rlc b ;
rr d ;/
ld a,[xreg]
rra
jr nc,nolft
or a ;cy=0
rr d
nolft:
ld [hxreg],a
ld a,d ;pixel value
ld [temp],a ;pixel value
ld hl,5000h ;\
ld a,[yreg] ;
srl a ;\ ;
srl a ; ;
srl a ;/ ;
ld e,a ;
ld d,0 ;
ld b,8 ;
mult: ;
add hl,hl ;
jr nc,noadd ;
add hl,de ;
noadd: ;
djnz mult ;
ld [blkadd],hl ;/
ld a,[yreg] ;\
sla a ;\ ;
sla a ; ;
sla a ;/ ;
and a,38h ; calc vram address
ld h,a ;
ld l,0 ;
ld bc,[blkadd] ;
add hl,bc ;
ld bc,0c000h ;vram base ;
add hl,bc ;
ld hl,[hxreg] ;
add hl,bc ;/
ld a,[temp] ;pixel value ;\
ld ix,xreg ;
bit 0,[ix] ;
jr nz,plot ; draw pixel
or a,[hl] ;merge pixels ;
plot: ;
ld [hl],a ;/
ld bc,0001h
ld hl,[xreg]
or a ;cy=0
sbc hl,bc
jr c,nexy
ld [xreg],hl
jp loop2
nexy:
ld hl,160-1
ld [xreg],hl
ld hl,[yreg]
or a ;cy=0
sbc hl,bc
jr nc,newlin
ei
ret
newlin:
ld [yreg],hl
jp loop1
bytead: ;color palette (increasing luminance on green monitor)
db 0,1,2,4, 5,6,8,10, 12,14,16,18, 20,22,24,26
== Scanned Articles ==
