NES APU demo

sqr1.asm

.include "constants.inc"
.include "header.inc"

.segment "CODE"
.proc irq_handler
  RTI
.endproc

.proc nmi_handler
  RTI
.endproc

.import reset_handler

.export main
.proc main
  ; enables square-1 channel
  LDA #%00000001
  STA APUFLAGS

  ; sets duty cycle to 50% and max volume
  LDA #%10111111
  STA SQ1_ENV

  ; plays a C# note
  LDA #$C9
  STA SQ1_LO
  LDA #$00
  STA SQ1_HI

forever:
  JMP forever
.endproc

.segment "VECTORS"
.addr nmi_handler, reset_handler, irq_handler

.segment "CHARS"
.res 8192
.segment "STARTUP"

sqr1_sqr2_triangle.asm

.include "constants.inc"
.include "header.inc"

.segment "CODE"
.proc irq_handler
  RTI
.endproc

.proc nmi_handler
  RTI
.endproc

.import reset_handler

.export main
.proc main
  ; enables the square 1, square 2 and triangle channels
  LDA #%00000111
  STA APUFLAGS

  ; sets the square channel 1 duty cycle to 50% and max volume
  LDA #%10111111
  STA SQ1_ENV

  ; plays a C# note on the square channel
  LDA #$C9
  STA SQ1_LO
  LDA #$00
  STA SQ1_HI

  ; sets the square channel 2 duty cycle to 50% and max volume
  LDA #%10111111
  STA SQ2_ENV

  ; plays an E note on the square channel 2
  LDA #$A9
  STA SQ2_LO
  LDA #$00
  STA SQ2_HI

  ; disable triangle channel internal controllers and turns
  ; on the channel
  LDA #%10000001
  STA TRI_CTRL

  ; plays a G# note on the triangle channel
  LDA #$42
  STA TRI_LO
  LDA #$00
  STA TRI_HIGH

forever:
  JMP forever
.endproc

.segment "VECTORS"
.addr nmi_handler, reset_handler, irq_handler

.segment "CHARS"
.res 8192
.segment "STARTUP"

sqr2.asm

.include "constants.inc"
.include "header.inc"

.segment "CODE"
.proc irq_handler
  RTI
.endproc

.proc nmi_handler
  RTI
.endproc

.import reset_handler

.export main
.proc main
  ; enables square-2 channel
  LDA #%00000010
  STA APUFLAGS

  ; sets duty cycle to 50% and max volume
  LDA #%10111111
  STA SQ2_ENV

  ; plays an E note
  LDA #$A9
  STA SQ2_LO
  LDA #$00
  STA SQ2_HI

forever:
  JMP forever
.endproc

.segment "VECTORS"
.addr nmi_handler, reset_handler, irq_handler

.segment "CHARS"
.res 8192
.segment "STARTUP"

triangle.asm

.include "constants.inc"
.include "header.inc"

.segment "CODE"
.proc irq_handler
  RTI
.endproc

.proc nmi_handler
  RTI
.endproc

.import reset_handler

.export main
.proc main
  ; enables the triangle channel
  LDA #%00000100
  STA APUFLAGS

  ; disable triangle channel internal controllers and turn
  ; on the channel
  LDA #%10000001
  STA TRI_CTRL

  ; plays a G# note
  LDA #$42
  STA TRI_LO
  LDA #$00
  STA TRI_HIGH

forever:
  JMP forever
.endproc

.segment "VECTORS"
.addr nmi_handler, reset_handler, irq_handler

.segment "CHARS"
.res 8192
.segment "STARTUP"