[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Vaporware alert!] Portable Apple II Clone Concept
mdj wrote:
Michael J. Mahon wrote:
True, but reimplementing the Woz machine is not trivial, and using
a Disk ][ Controller would be kind of a tribute to a virtuoso design.
;-)
Indeed. It also gets around the problem of hard to find DB-19
connectors :-)
Good point! ;-)
I guess I envisaged just shifting the state machine into the PIC, which
should be simple enough by simply replicating the logic in software,
and using the PIC's other outputs to control motor on/off and stepper
motor phases. Using the whole card would require a fair number of I/O
pins from a micro, by the time you connected up the data bus plus
sufficient address lines, and then you still need to generate a clock
signal for it, but I guess that's simple enough circuitry. I'd say
either approach is about the same about of work.
Agreed.
It would, however, look really really cool having a little box with a
PC connection + a 50 pin card edge connector sitting exposed on it's
top surface ;-)
I have to admit, I really like that, too--and it pretty much eliminates
the need to label the box for its function. ;-)
The design serves other purposes too - it could just as easily drive a
UniDisk 3.5" - good for transferring IIGS titles or moving larger
amounts of data to a real Apple II.
I guess you know you're a member of the oily hand brigade when this
idea seems infinitely more appealing to a few days hacking Copy ][+ to
write to an image file as its destination media ;-)
As a long-time hardware/software guy, I always look for an elegant
software hack before turning into a solder slinger, but both domains
have their rewards. ;-)
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. ;-(
I wonder it this was an artifact of PC's being a lot slower a decade
ago, or some inherent limitation. I guess in a modern PC the parallel
port still hangs off a virtual ISA bus for compatibility, but I'm
unsure if this virtual bus still clocks along at 8Mhz
No, this was done on a very fast machine--in fact, that's why I thought
it would be quite easy. I was thinking about the PC and its parallel
port in the same way that I think about an Apple or a microcontroller/
All legacy I/O in PCs is controlled through several layers of bus
conversion, terminating in a virtual ISA bus running at original PC
speed. Not only is the ISA bus slow, there are lots of opportunities
for contention and non-deterministic delays getting to it from the
processor.
Needless to say, when I put a scope on the parallel port, I was
quite disillusioned. That's when I packed up my "trivial" design
and moved on to other things... ;-(
In any case, it might be worth checking out the throughput of
USB-Parallel dongles; these things might allow significantly higher
performance.
Bandwidth, maybe--latency, never. And deterministic timing--forget it!
USB is a *network*, not a bus!
Anything you attach to USB must be "loosely coupled" on a scale of
at least tens of microseconds.
-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."