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palette.asm
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palette.asm
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;
; Atari palette viewer
;
; by Oscar Toledo G.
; https://nanochess.org/
;
; Creation date: Nov/04/2022.
; Revision date: Nov/13/2022. Added NTSC definition to choose NTSC/PAL.
;
PROCESSOR 6502
INCLUDE "vcs.h"
NTSC = 1 ; Define to 1 for NTSC, 0 for PAL
FRAME_LOW = $0080
FRAME_HIGH = $0081
COLUMN = $0082
ORG $F000
START:
SEI
CLD
LDX #$FF
TXS
LDA #$00
CLEAR:
STA 0,X
DEX
BNE CLEAR
SHOW_FRAME:
LDA #$88
STA COLUBK
STA WSYNC
LDA #2
STA VSYNC
STA WSYNC
STA WSYNC
STA WSYNC
LDA #0
STA VSYNC
IF NTSC
LDX #36
ELSE
LDX #61
ENDIF
TOP:
STA WSYNC
DEX
BNE TOP
LDA #0
STA VBLANK
LDA FRAME_HIGH
ASL
AND #$0E
STA COLUMN
LDX #0
VISIBLE:
STA WSYNC
LDA #$0F
STA PF1
TXA
CLC
ADC COLUMN
STA COLUPF
STA WSYNC
STA WSYNC
STA WSYNC
STA WSYNC
STA WSYNC
STA WSYNC
STA WSYNC
STA WSYNC
STA WSYNC
LDA #$00
STA PF1
STA WSYNC
STA WSYNC
TXA
CLC
ADC #$10
TAX
BCC VISIBLE
LDA #2
STA VBLANK
IF NTSC
LDX #30
ELSE
LDX #55
ENDIF
BOTTOM:
STA WSYNC
DEX
BNE BOTTOM
INC FRAME_LOW
BNE L1
INC FRAME_HIGH
L1:
JMP SHOW_FRAME
ORG $FFFC
.word START
.word START