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   ldx #$FF
   stx $8000 ; select last PRG bank
   inx
   stx $5000 ; mapper 028 address $00 (CHR register)
   stx $8000 ; PRG bank 0 on UNROM, CHR bank 0 on 028
   inx
   stx $5000 ; restore mapper 028 address $01 (PRG register)
   ldx $BFFF ; 0 in bank 0, high byte of IRQ vector (>$C0) in last bank

   bmi ShowQuitOptionOnTitleScreen

  lda $FFFC
  cmp #<reset
  bne ShowQuitOptionOnTitleScreen

;load x with amount of scanlines to wait, should not be zero

Scanline_counter:

   ldy #11   ;2 (not included in cycle count till end)
-
   nop ; 2
   nop ; 2
   dey   ; 2
;branch not taken requires two machine cycles. Add one if the branch is taken
   bne -   ;3 (2 on last loop) =9*11-1...98

   txa ; 2 = 100
   lsr a ; 2 = 102 (set carry half of the time)
   bcc + ;2 or 3 (depending if branch taken) = 104/5
+
   nop ; 2 = 106/7
   dex   ; 2 = 108/9
   bne Scanline_counter ;3 (2 on last loop) = 111/12
      ; +2 (ldy at the top)=113/114 (as stated, one less on last loop)
      
   rts ; overhead, not counted...6
   
; short about 1 cycle every 6 lines, not counting the overhead (113.5 vs 113.667)
; examples
;ldx #6 = 5.98 scanlines
;ldx #60 = 59.90 scanlines
;ldx #240 = 239.64 scanlines