background.asm

  .inesprg 1   ; 1x 16KB PRG code
  .ineschr 1   ; 1x  8KB CHR data
  .inesmap 0   ; mapper 0 = NROM, no bank swapping
  .inesmir 1   ; background mirroring
;;;;;;;;;;;;;;;
  .bank 0
  .org $C000 
RESET:
  SEI          ; disable IRQs
  CLD          ; disable decimal mode
  LDX #$40
  STX $4017    ; disable APU frame IRQ
  LDX #$FF
  TXS          ; Set up stack
  INX          ; now X = 0
  STX $2000    ; disable NMI
  STX $2001    ; disable rendering
  STX $4010    ; disable DMC IRQs

vblankwait1:       ; First wait for vblank to make sure PPU is ready
  BIT $2002
  BPL vblankwait1

clrmem:
  LDA #$00
  STA $0000, x
  STA $0100, x
  STA $0300, x
  STA $0400, x
  STA $0500, x
  STA $0600, x
  STA $0700, x
  LDA #$FE
  STA $0200, x
  INX
  BNE clrmem
   
vblankwait2:      ; Second wait for vblank, PPU is ready after this
  BIT $2002
  BPL vblankwait2


LoadPalettes:
  LDA $2002             ; read PPU status to reset the high/low latch
  LDA #$3F
  STA $2006             ; write the high byte of $3F00 address
  LDA #$00
  STA $2006             ; write the low byte of $3F00 address
  LDX #$00              ; start out at 0
LoadPalettesLoop:
  LDA palette, x        ; load data from address (palette + the value in x)
                          ; 1st time through loop it will load palette+0
                          ; 2nd time through loop it will load palette+1
                          ; 3rd time through loop it will load palette+2
                          ; etc
  STA $2007             ; write to PPU
  INX                   ; X = X + 1
  CPX #$20              ; Compare X to hex $20, decimal 32 - copying 32 bytes = 4 sprites
  BNE LoadPalettesLoop  ; Branch to LoadPalettesLoop if compare was Not Equal to zero
                        ; if compare was equal to 64, keep going down              
              
              
LoadBackground:
  LDA $2002             ; read PPU status to reset the high/low latch
  LDA #$20
  STA $2006             ; write the high byte of $2000 address
  LDA #$00
  STA $2006             ; write the low byte of $2000 address
  LDX #$00              ; start out at 0
LoadBackgroundLoop:
  LDA background, x      ; load data from address (background + the value in x)
  STA $2007              ; write to PPU
  INX                    ; X = X + 1
  CPX #$F0              ; Compare X to hex $FF, decimal 16*16 - copying 4kb
  BNE LoadBackgroundLoop ; Branch to LoadBackgroundLoop if compare was Not Equal to zero
                         ; if compare was equal to 128, keep going down
  LDX #$00              ; start out at 0
LoadBackgroundLoop2:
  LDA background+256, x      ; load data from address (background + the value in x)
  STA $2007              ; write to PPU
  INX                    ; X = X + 1
  CPX #$F0              ; Compare X to hex $FF, decimal 16*16 - copying 4kb
  BNE LoadBackgroundLoop2 ; Branch to LoadBackgroundLoop if compare was Not Equal to zero
                         ; if compare was equal to 128, keep going down
  LDX #$00              ; start out at 0
LoadBackgroundLoop3:
  LDA background+512, x      ; load data from address (background + the value in x)
  STA $2007              ; write to PPU
  INX                    ; X = X + 1
  CPX #$F0              ; Compare X to hex $FF, decimal 16*16 - copying 4kb
  BNE LoadBackgroundLoop3 ; Branch to LoadBackgroundLoop if compare was Not Equal to zero
                         ; if compare was equal to 128, keep going down
  LDX #$00              ; start out at 0
LoadBackgroundLoop4:
  LDA background+768, x      ; load data from address (background + the value in x)
  STA $2007              ; write to PPU
  INX                    ; X = X + 1
  CPX #$F0              ; Compare X to hex $FF, decimal 16*16 - copying 4kb
  BNE LoadBackgroundLoop4 ; Branch to LoadBackgroundLoop if compare was Not Equal to zero
                         ; if compare was equal to 128, keep going down


LoadAttribute:
  LDA $2002             ; read PPU status to reset the high/low latch
  LDA #$23
  STA $2006             ; write the high byte of $23C0 address
  LDA #$C0
  STA $2006             ; write the low byte of $23C0 address
  LDX #$00              ; start out at 0
LoadAttributeLoop:
  LDA attribute, x      ; load data from address (attribute + the value in x)
  STA $2007             ; write to PPU
  INX                   ; X = X + 1
  CPX #$F0              ; Compare X to hex $F0, decimal 16*16 - copying 256 bytes
  BNE LoadAttributeLoop  ; Branch to LoadAttributeLoop if compare was Not Equal to zero
                        ; if compare was equal to 128, keep going down

  LDA #%10010000   ; enable NMI, sprites from Pattern Table 0, background from Pattern Table 1
  STA $2000

  LDA #%00011110   ; enable sprites, enable background, no clipping on left side
  STA $2001

Forever:
  JMP Forever     ;jump back to Forever, infinite loop
  

NMI:
  LDA #$00
  STA $2003       ; set the low byte (00) of the RAM address
  LDA #$02
  STA $4014       ; set the high byte (02) of the RAM address, start the transfer
  ;RTI             ; return from interrupt
;;;;;;;;;;;;;;  
  
  .bank 1
  .org $E000
palette:
  .db $0F,$13,$23,$33,  $0F,$13,$23,$33,  $0F,$13,$23,$33,  $0F,$13,$23,$33 ;;background palette
  .db $0F,$13,$23,$33,  $0F,$13,$23,$33,  $0F,$13,$23,$33,  $0F,$13,$23,$33 ;;sprite palette

background:
  ;.db $00,$00,$00,$00,$00,$00,$00,$00, $00,$00,$00,$00,$00,$00,$00,$00

  .db $00,$00,$00,$00,$00,$00,$00,$00
  .db $00,$01,$02,$03,$04,$05,$06,$07,$08,$09,$0A,$0B,$0C,$0D,$0E,$0F
  .db $00,$00,$00,$00,$00,$00,$00,$00

  .db $00,$00,$00,$00,$00,$00,$00,$00
  .db $10,$11,$12,$13,$14,$15,$16,$17,$18,$19,$1A,$1B,$1C,$1D,$1E,$1F
  .db $00,$00,$00,$00,$00,$00,$00,$00

  .db $00,$00,$00,$00,$00,$00,$00,$00
  .db $20,$21,$22,$23,$24,$25,$26,$27,$28,$29,$2A,$2B,$2C,$2D,$2E,$2F
  .db $00,$00,$00,$00,$00,$00,$00,$00

  .db $00,$00,$00,$00,$00,$00,$00,$00
  .db $30,$31,$32,$33,$34,$35,$36,$37,$38,$39,$3A,$3B,$3C,$3D,$3E,$3F
  .db $00,$00,$00,$00,$00,$00,$00,$00

  .db $00,$00,$00,$00,$00,$00,$00,$00
  .db $40,$41,$42,$43,$44,$45,$46,$47,$48,$49,$4A,$4B,$4C,$4D,$4E,$4F
  .db $00,$00,$00,$00,$00,$00,$00,$00

  .db $00,$00,$00,$00,$00,$00,$00,$00
  .db $50,$51,$52,$53,$54,$55,$56,$57,$58,$59,$5A,$5B,$5C,$5D,$5E,$5F
  .db $00,$00,$00,$00,$00,$00,$00,$00

  .db $00,$00,$00,$00,$00,$00,$00,$00
  .db $60,$61,$62,$63,$64,$65,$66,$67,$68,$69,$6A,$6B,$6C,$6D,$6E,$6F
  .db $00,$00,$00,$00,$00,$00,$00,$00

  .db $00,$00,$00,$00,$00,$00,$00,$00
  .db $70,$71,$72,$73,$74,$75,$76,$77,$78,$79,$7A,$7B,$7C,$7D,$7E,$7F
  .db $00,$00,$00,$00,$00,$00,$00,$00

attribute:
  .db %00000000, %00000000, %00000000, %00000000, %00000000, %00000000, %00000000, %00000000
  .db %00000000, %00000000, %00000000, %00000000, %00000000, %00000000, %00000000, %00000000
  .db %00000000, %00000000, %00000000, %00000000, %00000000, %00000000, %00000000, %00000000
  .db %00000000, %00000000, %00000000, %00000000, %00000000, %00000000, %00000000, %00000000

  .org $FFFA     ;first of the three vectors starts here
  .dw NMI        ;when an NMI happens (once per frame if enabled) the 
                   ;processor will jump to the label NMI:
  .dw RESET      ;when the processor first turns on or is reset, it will jump
                   ;to the label RESET:
  .dw 0          ;external interrupt IRQ is not used in this tutorial
;;;;;;;;;;;;;;  
  
  
  .bank 2
  .org $0000
  .incbin "mario.chr"   ;includes 8KB graphics file from SMB1