Adressdecoding for Commodore 1541 Floppy Drive

[FraEgg]

Hello Michael,

I used your great Romulator 6502 in my Commodore 1541 floppy drive. I can now use many floppy speeders like DolphinDos etc. with it. However, there is a small improvement for your Romulator in a 1541 floppy drive. The IO ICs VIA are at address $1800 and $1C00 and are mirrored by the simple address decoding every 2K in the address space. This has the disadvantage that with the romulator from $2000 - $7FFF I cannot provide any additional memory through the romulator, as the VIAs then interfere with write accesses /WE. But I have found a solution. If you set the A15 on the mainboard address bus to high, then the VIAs no longer interfere and I can insert additional RAM from $2000-$BFFF. Then DOS and KERNAL appear. Maybe that would be a feature for the Romulator. I have an intermediate board running at the moment. But I think that something like this can also be built into the Romulator as a feature.

Logic:
Stop VIAs Mirroring on 1541 Floppydrive
------
CPU A15----+ |
CPU A14----+ OR + ----A15 Mainboard 1541 Floppydrive
CPU A13----+ |
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Greetings from Berlin
Frank