Xebec Posted July 25, 2017 Share Posted July 25, 2017 Hey folks -- According to this, If you have a PAL ANTIC (in a NTSC machine), a ROM change will trick PAL software into working. (With some some timing/color issues as others have noted) http://www.myatari.com/nirdary.html "In order to "trick" software programs written for PAL machines to make the software think it's running on a real PAL machine, a minor modification of the OS is required. The required modification was very simple: I just changed address $C386 to be "1" instead of "0"" .. If I have an Ultimate 1MB Upgrade and a PAL Antic - can I literally just edit the bit at $C386 in a ROM and upload that to the U1MB? Or is there some ROM encoding I need to consider first? Is C386 a hex address bit -- so I would go to position 50054 in the ROM file to make the change? Thanks, John H Quote Link to comment Share on other sites More sharing options...
Marius Posted July 25, 2017 Share Posted July 25, 2017 Not sure... But IIRC the OS does a checksum check on powerup. If it does not match it jumps into ram/rom test in selftest. I could be wrong... it has been quite a while since I modified OS ROMS... but I think it is true... Quote Link to comment Share on other sites More sharing options...
+DrVenkman Posted July 25, 2017 Share Posted July 25, 2017 Not sure... But IIRC the OS does a checksum check on powerup. If it does not match it jumps into ram/rom test in selftest. I could be wrong... it has been quite a while since I modified OS ROMS... but I think it is true... I don't think that's the case. I have a modified (padded out) version of OSb I use in my Ultimate 1MB for very rare instances when I need it; I've customized the Memo Pad header just a bit ... 1 Quote Link to comment Share on other sites More sharing options...
Roydea6 Posted July 25, 2017 Share Posted July 25, 2017 OSB has no self test check sum routine, so any modification is not noticed by the OS./or hardware. 2 Quote Link to comment Share on other sites More sharing options...
Rybags Posted July 25, 2017 Share Posted July 25, 2017 (edited) The XL OS keeps a flag in Ram to signify Pal/NTSC. But the 400/800 OS doesn't. I can't recall any 3rd party software that refers to it - the majority by far reads the PAL register on GTIA which in itself is flawed since it's Antic which determines if the system is 60/262 or 50/312. IMO it's practically pointless changing the OS like that, and it will screw with the tape bitrate lookup (not a huge problem). A benefit though is that it will correct the key auto-repeat which on a machine with PAL Antic/NTSC GTIA would otherwise slow down annoyingly. Edited July 25, 2017 by Rybags Quote Link to comment Share on other sites More sharing options...
Xebec Posted July 26, 2017 Author Share Posted July 26, 2017 So what bit do I modify on the ROM ? Quote Link to comment Share on other sites More sharing options...
Roydea6 Posted July 26, 2017 Share Posted July 26, 2017 So what bit do I modify on the ROM ? Read your first POST. Quote Link to comment Share on other sites More sharing options...
Xebec Posted July 26, 2017 Author Share Posted July 26, 2017 Read your first POST. I'd be modifying the ROM from a PC - so is $C386 the straight address from 0 or is there an offset? Quote Link to comment Share on other sites More sharing options...
Rybags Posted July 26, 2017 Share Posted July 26, 2017 The order of the OS when in Rom files should be: XL/XE 0000 - 0FFF corresponds to the OS normally living @ C000-CFFF 1000 - 17FF corresponds to the 2K Self-Test which switches in at 5000-57FF 1800 - 1FFF the FP Rom @ D800-DFFF 2000 - 3FFF the OS Rom @ E000-FFFF 400/800 0000 - 07FF FP Rom @ D800 0800 - 27FF OS Rom @ E000 3 Quote Link to comment Share on other sites More sharing options...
Kyle22 Posted July 27, 2017 Share Posted July 27, 2017 (edited) The XL/XE OS starts at $C000. If you are looking for what's in ROM at address $C386, then you would change $0386 in the ROM image. Edit: Clarification. Edited July 27, 2017 by Kyle22 Quote Link to comment Share on other sites More sharing options...
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