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Re: [Vaporware alert!] Portable Apple II Clone Concept

mdj wrote:


Michael J. Mahon wrote:



Yes, that was my conclusion, too.  Disk ][ controllers are quite
plentiful, so putting one inside the interface box seemed the most
straightforward solution.



Either that, or since the controller is so simple, just replacing its
functionality with PIC + 74LS since you're building a circuit anyway.


True, but reimplementing the Woz machine is not trivial, and using
a Disk ][ Controller would be kind of a tribute to a virtuoso design.
;-)


I did have some concerns about writing (I was mostly concerned with
reading).  There are lots of jitter sources in PCs that would require
some hardware solution for precisely timed write loads.



True. There might be just enough memory space inside a microcontroller
that an entire track can be buffered, but then the read/write logic
would need to written for the microcontroller instead.


That would be pushing 8KB, which I think of as a little large for
most PICs.  It would take an external SRAM.


Alternatively, the RTC in a PC has sufficient resolution to handle this
issue.


That seems the better approach--the microcontroller only needs to
implement a FIFO.


Accessing it inside of an OS like Windows would probably be
problematic. You could get away with it on Linux were you can manage
close enough to realtime scheduling + access to the RTC from a usermode
application. Personally I'd be more than happy with read-only; the idea
for me is to get data off obsolete media, not put it back on ;-)


That was my goal, too.


Another gotcha that's prevented me from playing with this extensively
in the past is the need for a -12V power source, which is something
that's not readily obtainable from a PC's user accessible ports and
power connectors. Somehow the thought of building power supplies makes
my teeth hurt :-)


I used a DC-DC converter for the negative voltages, but planned on
using an external power supply in any case.

I got as far as running a Disk ][, seeking the head, and trying
to read the head signal before finding that I couldn't read it fast
enough.  ;-(

-michael

Music synthesis for 8-bit Apple II's!
Home page:  http://members.aol.com/MJMahon/

"The wastebasket is our most important design
tool--and it is seriously underused."