11 May
2009
11 May
'09
8:12 p.m.
On 11 May 2009 at 22:26, Andrew Lynch wrote:
Hi Chuck! Thanks! By extensions, I mean the Disk IO
has a regular
Shugart mini-disk interface with all the usual signals and options.
It also has the "feature" interface which imports/exports the rest of
the NEC765/i8272 signals necessary for 8" and other drive support. An
8" drive cable with what signals are needed for that drive could be
fabricated using the Shugart mini-disk interface plus whatever
signals/options are needed from the feature connector. The 8" drive
cable would be custom to Disk IO and that drive but there are multiple
8" drive interfaces so that seemed to me to be the most flexible way
to provide support in a limited PCB space format.
Hi Andrew,
Good work!
I did check out your schematic (I think)--FDC_A.jpg and FDC_B.jpg and
I don't see the "special feature" connector anywhere.
Here are my comments on what I see, they're only speculation and
opinion, so please don't take them for anything more than that. I'm
certain that you had good reasons for doing what you did the way you
did it!
One of the problems with using a 4MHz Z80 on a raw data stream is
that the Z80A isn't fast enough to handle it. While a uC might do
that, the simplest seems to be the Catweasel's use of a 128K time-
domain memory. Leave it to the host processor to crunch the data
later. One could well more easily hook up a uC to the raw disk
interface, don't you think?
How does one derive the RWC/TG43 signal that some 8" drives require?
If there's an 8" connector, why is HDL not brought to it?
One thing that I'm not certain of is the use of the US0 and US1 pins
for select. The PC uses a separate register for select and leaves
US0 and US1 NC. I suspect that this bears on some aspect of 5.25"
operation and the 765's polling mode, but I'm not certain.
Would it be better to multiplex the READY signal to a set of jumpers
that allows one to select either the drive's own ready (all 8" drives
and most 5.25" have this) or a tied-high READY?
FWIW, the Victor 9000 disk format is variable datarate (or CLV,
depending on how you want to look at it).
Best regards as always,
Chuck