Program 8. pg 233›0000        10  .PAGE›            11 ;›            12 ;necessary operating system and hardware equates›            13 ;›026F        14 GPRIOR = $026F ;GTIA priority control (shadow)›D01A        15 COLBK  = $D01A ;background color register›D01B        16 PRIOR  = $D01B ;GTIA priority control (hardware)›D40A        17 WSYNC  = $D40A ;horizontal blank synchronization›            18 ;›            19 ;›0000        20  *= $0600›            21 ;›            22 ;this service routine for the display list interrupt›            23 ;can be placed anywhere in RAM, and was placed on page six›            24 ;only for purposes of demonstration›            25 ;›            26 ;begin interrupt service routine code›            27 ;›            28 ;save contents of accumulator›            29 ;›0600 4B     30  PHA›            31 ;›            32 ;get the multicolor player, fifth player, and priority bits›            33 ;››0601 AD6F02 34  LDA GPRIOR›            35 ;›            36 ;force the GTIA mode select bits to zero but save the other bits›0604 293F   37  AND #$3F›            38 ;›            39 ;wait until next scan line for a nice clean change›            40 ;›0606 8D0AD4 41  STA WSYNC›            42 ;›            43 ;change hardware register until VBLANK›            44 ;›0609 8D1BD0 45  STA PRIOR›            46 ;›            47 ;reset COLOR4 to zero (for modes 9 and 11)›060C A900   48  LDA #$00›060E 8D1AD0 49  STA COLBK›            50 ;›            51 ;restore accumulator›            52 ;›0611 68     53  PLA›            54 ;›            55 ;return from the display list interrupt›            56 ;›0612 40     57  RTI›            58 ;›            59 ;end of interrupt service routine›            60 ;›