Hello, I found (http://www.io.com/~nickb/atari/) this
site looking for classic games (Mame32, SNES, Atari)
and decided to try to learn Atari programming, since
all the resorces were there.
I need a little help, and later a lot of help.
trying to understand other people's code I came across
this:
"6 digit score display" - by Robin Harbron
adc #<zero
adc #>zero
what does it all mean?? - some kind of adressing mode
or assembler directive
and what the diff.
adc #zero or adc zero
I've been learning atari for about 2 week, I have a
very basic understanding and somewhat understand 6502
assembly from my VIC-20 days.
below is my 1st program, and working on something just
a little more chalenging now.
current proj. ATARI
last Proj. OPIC: http://www.geocities.com/tim300cx5/
;by Tim Salazar
processor 6502 ;compile for the 6502 processor
include vcs.h ;convenience names for ram <$80
org $F000 ;start prog. adresss
CountLow = $80 ;Playfield count
Timer = $84 ;count down pause (to slow things down)
Start
SEI ;SEt Interrupt disable
CLD ;CLear Decimal mode
LDX #$FF ;LoaD X - with #$FF (255)
TXS ;Transfer X to Stack pointer
LDA #0 ;LoaD A - with 0
ClearMem
STA 0,X
DEX
BNE ClearMem
LDA #$01
STA COLUBK ;set background colour (1)drk gray
LDA #$F0
STA COLUPF ;set play field colour ($f0)drk brown
LDA #$02
STA Timer ;Timer=2 (chang screen every 2/60th sec.)
LDA #$01
STA CTRLPF ;set bit(d0) to 1 to mirror left half
MainLoop
LDA #2 ;
STA VSYNC ;set (d1) bit of vert. sync (on)
STA WSYNC ;waits till leading edge of horizontal
blank
STA WSYNC
STA WSYNC
LDA #43
STA TIM64T
LDA #0
STA VSYNC ;Done with VSYNC'ing
DEC Timer
BNE WaitForVblankEnd
INC CountLow
LDA #$02
STA Timer
WaitForVblankEnd
LDA INTIM
BNE WaitForVblankEnd
LDY #191
STA WSYNC
STA VBLANK
LDA CountLow
TAX
STA WSYNC
ScanLoop ;Now scanning visable screen
STA WSYNC
LDA CountLow
STA PF2
STX COLUBK
DEX
DEY
BNE ScanLoop
LDA #2
STA WSYNC
STA VBLANK
LDX #30
OverScanWait
STA WSYNC
DEX
BNE OverScanWait
JMP MainLoop
org $FFFC
.word Start
.word Start
; So simple
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