Phil Dumpster wrote:
"Michael J. Mahon" wrote:
And if you think that transferring images at 19200 baud is a pain,
wait until you find out about the special hardware you'll need to
attach an Apple drive to a PC. ;-) Writing Apple II disks on a
PC is not possible without unusual hardware and software which
is much harder to find and use than ADT.
Has anyone ever tried to build a bus converter to adapt the 62 pin 8 bit
ISA
bus to the peculiarities of the apple bus? You would then be able to put a
real
disk II controller into an ISA machine and then be able to use it with some
dedicated software that would emulate the apple operating system, at least as
far as the disks were concerned.
Seems to me the hardware would be trivial - the 64K memory space of the
apple
bus could be mapped into the D or E block of the ISA machine. Slot select
signals could be generated the same way they are on a real apple. Only bus
timing might be a little sticky but could be accounted for.
I went down this path a few years ago... My first idea was to simply
interface a Disk ][ drive to the PC parallel port--it has enough inputs
and outputs to control the drive. Then I discovered that, regardless
of the speed of the processor, the maximum sampling rate of a signal
on the parallel port is limited by the (often virtual) ISA bus to about
500kHz--not fast enough to do direct head signal decoding (which
requires about 2MHz sampling).
Next idea was to interface a Disk ][ Controller card to the parallel
port, which could be done, but would require a couple of clocks to
be generated outside the PC, so a medium-sized box would be
required between the parallel port and the Disk ][, with external
power supply.
Both solutions would have required re-writing RWTS for the PC
(an amusing task except for the difficulty of getting tight real-time
control on the PC).
At this point I reevaluated the situation and noted that adapting a
Disk ][ Controller to the ISA bus would eliminate some parallel
port issues (but still have ISA timings) and the need for an external
power supply and box.
This still seems to be the "path of least resistance" for accessing
Apple II disks on a PC (I have no Catweasel experience, and that
community seems to have little interest in Apple II's). It would
require some hardware hacking a PC and a PC version of RWTS
(with timing finessed, somehow...). Since my primary interest
was _reading_ Apple II disks, I would have been willing to re-read
several times to get a track read--a way of tolerating the timing
glitches caused by interrupts in the PC/Windows environment.
The combined effects of my having access to other convenient
ways to get bits back and forth between my Apples and my PCs
and the obsolescence of the ISA bus have caused me to put
this on the "back burner". ;-)
Maybe someone else will take a run at it...
-michael