C128 assembly program

silly-slide

. 1800 LDX #$00         # This clears the SID memory
       LDA #$00
       STA $D400,X
       INX
       CPX #$29
       BNE $1804

. 180C LDX #$0F         # Set master volume
       STX $D418
       LDX #$4F         # Set attack/decay
       STX $D405
       LDX #$08         # Set duty cycle high byte
       STX $D403
       LDX #$00         # Set frequency high byte.
       STX $D401
       LDX #$41         # Pulse, gate on
       STX $D404

. 1825 LDA $D012        # Vertical refresh wait
       CMP #$FF
       BNE $1825

       CLC              # Add to frequency
       LDA #$03         
       ADC $D400
       LDA #$00
       ADC $D401
       STA $D401
       CMP #$F0         # If frequency not tapped, blah.
       BPL $1825

       LDA #$0B         # Shorten decay for the last.
       STA $D405

. 1846 LDX #$00
. 1848 LDA $D012        # Vertical refresh wait again.
       CMP #$FF
       BNE $1848
       INX
       CPX #$20
       BNE $1848
       BRK

J F1800