Issue 24 October 2008
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  SEI         ; Set the interrupt flag, disabling interrupts 
              ; needs to be done or the cpu will crash during
              ; execution of an IRQ set-up

  LDA#$37     ; For this example tutorial, make sure the     
  STA$01      ; Kernal is enabled by configuring the mem config register.

  LDA#$00     ; Initialise music by loading A with zero (song
  JSR$1000    ; number for most players) and call the address.

  LDA#$01     ; Set raster IRQ compare flags, needed during
  STA$D01A    ; and IRQ execution.
  STA$D019    ;

  LDA#$7F     ; Set CIA register bits to check for IRQ
  STA$DC0D    ; interrupt during each frame.
  LDA$DC0D    ; Latch $DC0D register.

  LDA#$0F     ; Set the IRQ vector addresses with the address
  STA$0315    ; of the interrupt execution program. This example is
  LDA#$30     ; memory location $0F30. $0315 stores the most
  STA$0314    ; significant byte, where $0314 stores the least.

  LDA#$68     ; Set target interrupt raster line. This will     
  STA$D012    ; be the raster position when an interrupt is detected.

  LDA#$1B     ; Set gfx mode to text view and MSB of raster to
  STA$D011    ; zero.

  CLI         ; Clear Interrupts

  RTS         ; Return from Subroutine (back to point of caller)

  LDA$D012    ; Check the raster line is equal or over the     
  CMP$D012    ; target raster line before continuing, BNE$0F33  
              ; branching back if not equal. "$0F33"           
              ; represents the jump address.

  DEC$D020    ; Decrease border colour by 1
  JSR$1003    ; Call music play address to play music each frame.

  INC$D020    ; Increment border colour this will show a change 
              ; in the border colour and show how many         
              ; raster lines are used in the music player

  LDA#$01     ; Reset Raster irq flag to run another raster       
  STA$D019    ; IRQ check at the frame.

  JMP$EA31    ; Jump to Kernal routine that loads registers to       
              ; original states and returns from interrupt.

+------------------------------------------------------------+
|Raymond C. Bryan 651-642-9890 vox   |The battle is sometimes|
|Raymond Computer 651-642-9891 fax   |to the small for       |
|2402 Univsity Ave  -email: raycomp  |the bigger they are    |
|St Paul MN 55114  _at_visi_dot_com  |the harder they fall.  |
|USA Amiga - Commodore               |James Thurber          |
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