Changes
== I/O Port Address ==
The project is rather unclear about the recommended I/O address: The Decoder's (used in the CPC example source code uses ) is Port F8F0h(ie. However, shorten Link 1 on the [[Maplins 8bit Input Port project ]]). Bit7 Dotclock (probably derived from E.O.C.) (end of ADC conversion) Bit6 Sync (used as hsync) (which is, among others, explicitely intended for use with the Decodersample program doesn't seem to do any vsync handling?) does use Port F8Exh. Bit5-4 Unknown/unused Bit3-0 Luminance
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 ==
Here is a commented version of the original sample code...
--- basic code ---
5 MEMORY 30000:MODE 2
10 LOAD"wefax1.obj"
20 INPUT "enter horizontal resolution 1-4";resh
30 IF resh>0 AND resh<5 THEN POKE <resmod>,resh ELSE CLS:GOTO 20
40 CALL <entryoint>
50 CALL <rerun>
60 GOTO 50
--- asm 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: ;--- y loop ---
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: ;--- x loop ---
di
resmod equ $+1 ;\horizontal resolution
ld d,2 ;<-- MODIFIED (1..4) ;/
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 ; next x
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 ; next y
jr nc,newlin ;
ei ;frame done ;
ret ;return to basic ;
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 ==
* Weather Satellite Down Converter – Part 2 - project 23 (not yet scanned, does somebody have it on paper?)
* Weather Satellite Prediction Table - project 24 (not yet scanned, does somebody have it on paper?)
[[Category:Peripherals]]
