Re: VC1541 with fast serial?

Den Mon, 26 Aug 2019 14:18:11 +0200 skrev Gerrit Heitsch
<gerrit_at_laosinh.s.bawue.de>:
> On 8/26/19 2:02 PM, groepaz_at_gmx.net wrote:
> > Am Montag, 26. August 2019, 13:53:21 CEST schrieb afachat_at_gmx.de:
> >> Hi there,
> >>
> >> has anyone actually every tried to convert the VC1541 to use the
> >> fast serial bus of the C128?
> >>
> >> As I see it, on the UC3 VIA here
> >> http://www.zimmers.net/anonftp/pub/cbm/
> >> schematics/drives/new/1541/short-251748-rev.E-left.gif there still
> >> are
> >>
> >> - Port A0-7
> >> - CB1
> >> - CB2
> >>
> >> unconnected. These could be used to
> >>
> >> - CB1/2 shift out under T2 control and
> >> - PA0-7: connected to a 74LS164 serial-to-parallel shift-in
> >> register
> >>
> >> The only other thing needed would probably be a 74LS14 Schmitt
> >> trigger input driver, a 7406 output driver, and potentially
> >> replacing the PB6 drive ID input with an SRQIN input, and of
> >> course a fly-wire to the IEC's SRQIN pin 1.
> >>
> >> What do you think?
> > 
> > you also need some extra synchronisation to eliminate the via bug
> > with external clocking (which is basically the reason for why its
> > not used in the 1541). i vaguely remember it being described in
> > either one of the datasheets, or perhaps application notes.
> 
> It might be easier to do what Commodore has done in the 1570/71 and
> use an additional 6526 just for the shift register. Then borrow the
> code from the 1571.

That would most likely be the solution that requires the least amount
of work to get it up and running. 

Captain Obvious says that the con is of course that it needs a CIA. For
a one-off or general DIY project that might not be a problem, but if
someone were to order a bunch of PCBs and sell either as a complete kit
or ready-built thing it might be troublesome to source CIAs.

Since the source code seems to be available for the 1570/1571, it might
be rather easy to lobotomize the MFM code from it.
http://www.zimmers.net/anonftp/pub/cbm/src/drives/index.html

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