mirror of https://github.com/stella-emu/stella.git
193 lines
1.7 KiB
NASM
193 lines
1.7 KiB
NASM
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;;A demo using CBS Electronic's FA (12K) + RAM (256 bytes) bankswitching scheme
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;;3/20/09 By: Rick Skrbina
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processor 6502
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include "vcs.h"
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include "macro.h"
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;BG_Color_Read equ BG_Color_Write+256
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;PF_Color_Read equ PF_Color_Write+256
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;BG_Write equ $1000
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BG_Read equ BG_Write+256
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PF_Read equ PF_Write+256
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seg.u RIOT_vars
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org $80
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seg.u FA_RAM_vars
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org $1000
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BG_Write ds 1
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PF_Write ds 1
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seg bank_0
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org $D000
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rorg $F000
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repeat 512
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.byte $D0
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repend
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Bank0
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nop
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nop
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nop
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CLEAN_START
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lda #$FF
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sta PF_Write
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sta PF1
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lda #$0F
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sta COLUBK
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Start_Frame
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lda #2
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sta VBLANK
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sta VSYNC
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sta WSYNC
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sta WSYNC
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sta WSYNC
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lda #0
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sta VSYNC
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ldy #37
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VerticalBlank
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sta WSYNC
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dey
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bne VerticalBlank
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lda #0
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sta VBLANK
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ldy #192
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Picture
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sta WSYNC
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dey
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bne Picture
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lda #2
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sta VBLANK
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ldy #30
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Overscan
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sta WSYNC
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dey
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bne Overscan
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jsr Switch_To_1
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jsr Switch_To_2
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lda BG_Read
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sta COLUBK
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lda PF_Read
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sta COLUPF
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jmp Start_Frame
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org $D300
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rorg $F300
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Switch_To_1 ;$F300
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lda $FFF9
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nop
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nop
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nop
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nop
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nop
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nop
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rts
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Switch_To_2 ;$
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lda $FFFA
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nop
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nop
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nop
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nop
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nop
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nop
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rts
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org $DFFC
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rorg $FFFC
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.word Bank0
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.byte "B0"
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seg bank_1
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org $E000
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rorg $F000
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repeat 512
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.byte $00
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repend
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Bank1
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lda $FFF8
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Change_BG_Color
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clc
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lda BG_Read
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adc #1
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sta BG_Write
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rts
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org $E303
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rorg $F303
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jsr Change_BG_Color
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lda $FFF8
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org $EFFC
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rorg $FFFC
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.word Bank1
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.byte "B1"
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seg bank_2
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org $F000
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rorg $F000
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repeat 512
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.byte $00
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repend
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Bank2
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lda $FFF8
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Change_PF_Color
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sei
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lda PF_Read
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sbc #1
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sta PF_Write
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rts
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org $F30D
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rorg $F30D
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jsr Change_PF_Color
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lda $FFF8
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org $FFFC
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rorg $FFFC
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.word Bank2
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.byte "B2"
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