first

background/background.asm

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+  .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 $0200, x
+  STA $0400, x
+  STA $0500, x
+  STA $0600, x
+  STA $0700, x
+  LDA #$FE
+  STA $0300, x
+  INX
+  BNE clrmem
+   
+vblankwait2:      ; Second wait for vblank, PPU is ready after this
+  BIT $2002
+  BPL vblankwait2
+
+
+  LDA #%11111111   ;intensify blues
+  STA $2001
+
+Forever:
+  JMP Forever     ;jump back to Forever, infinite loop
+  
+ 
+
+NMI:
+  RTI
+ 
+;;;;;;;;;;;;;;  
+  
+  
+  
+  .bank 1
+  .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

background/background.bat

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+NESASM3 background.asm
+pause

background/background.fns

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+; background.asm
+Forever                          = $C042
+vblankwait1                      = $C014
+vblankwait2                      = $C038
+clrmem                           = $C019
+RESET                            = $C000
+NMI                              = $C045