Differences between the KERNAL ROMs 901486-06 and 901486-07 Apparently, 901486-06 is only for NTSC-M systems with 14318181/14 Hz clock frequency and a 6560 video chip. The 901486-07 ROM is for PAL-B systems with 17734472/16 Hz clock frequency and a 6561 video chip. "<" = 901486-06 ">" = 901486-07 First, there is a difference at $e475. It must be a version number or something. < e470: c6 58 4c 74 c4 41 20 33 c5 4c 77 c6 ff ff ff ff : .XLt.A 3.Lw..... --- > e470: c6 58 4c 74 c4 e8 20 33 c5 4c 77 c6 ff ff ff ff : .XLt.. 3.Lw..... Then there is the video chip initialization table, which gets copied from $ede4 to $9000. The horizontal and vertical screen origin coordinates differ. < ede0: ff ff ff ff 05 19 16 2e 00 c0 00 00 00 00 00 00 : ................ --- > ede0: ff ff ff ff 0c 26 16 2e 00 c0 00 00 00 00 00 00 : .....&.......... 60 Hz VIA timer ($4289+2=17035 on R6, $4826+2=18472 on R7): < fe30: ef a9 82 8d 1e 91 20 8d ef a9 c0 8d 2e 91 a9 89 : ...... ......... < fe40: 8d 24 91 a9 42 8d 25 91 60 85 b7 86 bb 84 bc 60 : .$..B.%.`......` --- > fe30: ef a9 82 8d 1e 91 20 8d ef a9 c0 8d 2e 91 a9 26 : ...... ........& > fe40: 8d 24 91 a9 48 8d 25 91 60 85 b7 86 bb 84 bc 60 : .$..H.%.`......` Table of RS-232 timing constants: < ff50: 91 ae 98 02 86 a8 68 a8 68 aa 68 40 92 27 40 1a : ......h.h.h@.'@. < ff60: c6 11 74 0e ee 0c 45 06 f1 02 46 01 b8 00 71 00 : ..t...E...F...q. < ff70: 2a 00 48 8a 48 98 48 ba bd 04 01 29 10 f0 03 6c : *.H.H.H....)...l --- > ff50: 91 ae 98 02 86 a8 68 a8 68 aa 68 40 e6 2a 78 1c : ......h.h.h@.*x. > ff60: 49 13 b1 0f 0a 0e d3 06 38 03 6a 01 d0 00 83 00 : I.......8.j..... > ff70: 36 00 48 8a 48 98 48 ba bd 04 01 29 10 f0 03 6c : 6.H.H.H....)...l