On Wed, Jan 9, 2019 at 12:45 PM Gerrit Heitsch <gerrit@laosinh.s.bawue.de> wrote: > > On 1/9/19 12:08 PM, Francesco Messineo wrote: > > On Wed, Jan 9, 2019 at 12:02 PM <silverdr@wfmh.org.pl> wrote: > >> > >> > From what I read, Commodore had planned to do a rework of the 1541 > using a 6526 (probably like in the 1570/71, or just replacing one 6522 > with a 6526), but someone deleted the necessary traces to use the shift > register from the C64 schematics and when that was found, they already > had a lot of boards produced. So they dropped the rework of the drive > and went with bit banging I/O. And they even had to slow that down > compared to the VIC-20 due to the badlines VIC-II introduced. > > I would really be interested in what would be necessary to get a C64 to > what was initially planned. see how they did the "burst mode" between 1571 and C128. On the 1571 there's an additional 6526 with only two pins used, they didn't even bother to substitute one of the 6522. Afair, on the C128 side, there's a cmos switch that routes the signals from the IEC bus either on the C64-like circuit or to the 6526 shifter register I/O (and the same cmos switch thing must be also on the 1571 side, I'm going from memory). The hardware part shouldn't be a problem, all i takes is more or less implement the C128/1571 burst mode. Of course both C64 and 1541 kernels would need to be patched, and that would render both not compatible with the rest of the world. FrankReceived on 2019-01-09 13:02:18
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