Am Mittwoch, 9. Januar 2019, 12:56:23 CET schrieb Gerrit Heitsch: > On 1/9/19 12:49 PM, groepaz@gmx.net wrote: > > Am Mittwoch, 9. Januar 2019, 12:45:05 CET schrieb Gerrit Heitsch: > >> On 1/9/19 12:08 PM, Francesco Messineo wrote: > >>> On Wed, Jan 9, 2019 at 12:02 PM <silverdr@wfmh.org.pl> wrote: > >>>>> On 2019-01-09, at 11:43, Francesco Messineo > > > > <francesco.messineo@gmail.com> wrote: > >>>>>> At least IEC still allows more than two devices ;-) > >>>>>> > >>>>>> But no, the IEC on the C64 is another example of CR(ippled) hardware, > >>>>>> plus VIA-bug workaround ridden implementation. Its big brother GPIB, > >>>>>> while predating both, wasn't bad though.>>> > >>>>> > >>>>> Yes it was slow, but I couldn't think about a better compromise, > >>>>> really. > >>>> > >>>> The major issue was actually the speed - not really of the bus but of > >>>> the > >>>> 1541 implementation with 6522 software workarounds making the bus look > >>>> worse than it really was. Common thing was to add at least the parallel > >>>> connection to 1541, bringing it somewhat closer to the original GPIB. > >>>> And yes - it still allowed more than two devices and obviously not only > >>>> the floppy drives.> > >>> > >>> Yes, that was due to a bug in the 6522 chip. And sure, one of the > >>> first things that I purchased when I could, was the speeddos mod, > >>> even if I needed to go back to plain IEC speed whenever I wanted to > >>> plug the super-fast 300 bps user port modem :) > >>> > >> 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. > > > > http://a1bert.kapsi.fi/Dev/burst/ - VICE emulates this, and the C64RMK2 > > can do it too > > Ok, I wrote it in a way that is easy to misunderstand... This would also > include what would need to be done to a 1541 to change it. > > Would it be possile to replace one of the 6522 with a 6526 plus some > software adjustments or would you have to add a 6526? i'd say it can be done as you say... however the software changes would be quite massive, i guess. which probably is the reason for why the 6526 is ONLY used for burstmode in 157x (you can remove it if you dont use burstmode) -- http://hitmen.eu http://ar.pokefinder.org http://vice-emu.sourceforge.net http://magicdisk.untergrund.net PROGRAM n. A magic spell cast over a computer allowing it to turn one's input into error messages. tr.v. To engage in a pastime similar to banging one's head against a wall, but with fewer opportunities for reward.Received on 2019-01-09 14:01:53
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