Re: Did Commodore cheat with the quad density floppies?

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?

  Gerrit