[stella] More complicated differences between 6502 and 6507?

Subject: [stella] More complicated differences between 6502 and 6507?
From: Oliver Achten <achten@xxxxxx>
Date: Sun, 14 Oct 2001 17:32:32 +0200 (MEST)
Hello guys!

I have a question concerning (possible) internal differences between the
6502 and the 6507. I am currently working on my "Super VCS" Project, that means,
i have developed a small board which plugs into the 6507 Socket, which
consists of 8K BIOS ROM, 32KB SRAM, a 6502 CPU and a 6522 VIA. With this
modification, you can download binaries via the Parallel Port into the 32K SRAM and
execute them, including full VCS compability (switching off the upper Adress
lines A13-A15 and write protect the RAM). The system is currently running and
working, BUT, from testing nearly every PAL rom i found, i discovered 3 ROMS
which behave strange. In Dodge'em, the scoreboard is messed up (reversed
digits, wrong SOund effects), in Haunted House, the Player is misplaced on the
left side (the game is not Playable), and in Berzerk, the PLAYER missile is
visible on the left side in the opening screen ((C) 1982 ATARI ). This happens
also, when i plug in the original cartridge (the external Adress lines
disabled). Since every complicated kind of game is working (e.g. Solaris, Demon
Attack), i question myself if there are any internal differences between the 6502
and the 6507. Theoretically, there shouldn´t. I´m using a original MOS6502
CPU from a 1541 Floppy. HAs anyone information about this?

Thank you for your patience! :)


      Oliver achten

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