Re: Did Commodore cheat with the quad density floppies?

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.

  Gerrit