5 Jan
2013
5 Jan
'13
2:06 a.m.
Howdy folks.
I have a handful of 5.25" floppy disks for an Ohio Scientific C1, which I would like
to image. Anyone have any info on this disk format, or know of a tool that can read them?
They don't appear to be in a WD177x-style format... at least not one intelligible to
ImageDisk or Tim Mann's catweasel tools. There is at least one C1 emulator out there
with support for disk image files, so I have some hope somebody's already done the
dirty work for me.
If nothing already exists, low-level info on the format would be awesome as then I'd
have something to work with, trying to extend Karsten Scheibler's catweasel tools.
A few cursory trudges through t3h Googles have borne little fruit so far.
ok
bear.
--
until further notice
5 Jan
5 Jan
3:45 p.m.
On Sat, Jan 05, 2013 at 02:06:32AM -0800, r.stricklin wrote:
Howdy folks.
I have a handful of 5.25" floppy disks for an Ohio Scientific C1, which
I would like to image. Anyone have any info on this disk format, or know
of a tool that can read them?
For the 8" disks OSI used a serial chip to write data to the drive. The
drive had an internal data separator. I think the 5.25" used the same
format. Its incompatible with any normal disk controller chip. Only raw
transition tools could image the disk.
If you have an OSI a dump program is here
http://osiweb.org/software.html
This thread previously discussed it. It seemed to conclude none of the
current tools have been programmed to decode that format.
http://www.classiccmp.org/pipermail/cctalk/2012-February/312129.html
The source code for the dumper may give you info on decoding the
format. I may be able to dig up where the 8" format is documented if
it helps.
6 Jan
6 Jan
1:47 a.m.
bear (r.stricklin) wrote:
Howdy folks.
I have a handful of 5.25" floppy disks for an Ohio Scientific C1, which I would like
to image. Anyone have any info on this disk format, or know of a tool that can read them?
They don't appear to be in a WD177x-style format... at least not one intelligible to
ImageDisk or Tim Mann's catweasel tools. There is at least one C1 emulator out there
with support for disk image files, so I have some hope somebody's already done the
dirty work for me.
The winOSI emulator uses a raw disk dump format.? The dump can be produced, as
David G. pointed out, using the disk dump utility.
For a detailed discussion of the disk format, look at The OSI Gazette, Compute! #20, Jan
1982.? The Gazette in issue #21 contains a discussion of the disk routines.? Both are
available at http://www.osiweb.org/journals.html#Computes_Gazette
OSI (Meaning Mike Cheiky) used a regular UART to write the data stream to the disk, using
discrete TTL logic and one-shots to do the MFM encoding and decoding, and a standard PIA
chip to drive the floppy control lines, managing the disk state in software.? This allowed
OSI to have a disk interface before the standard chips were available.? (At the time, S100
systems handled disk interfacing with boards full of TTL; Apple handled it by having Woz
and a few chips; and CBM hoped to use the GPIB interface to get a disk for free, but it
didn't work out that way).? So all in all, you have to hand it to Cheiky for coming up
with a cheap solution based on commodity chips--not as clever as Woz's interface, but
since OSI had less cloud with drive manufacturers than apple, it was a win to be able to
use a standard drive.
If you make any images, I would be very interested in getting copies of them for the
archive.
Best regards,
Dave
4:23 p.m.
Dave wrote:
not as clever as Woz's interface, but since OSI
had less cloud with drive manufacturers than apple,
I don't think Apple had any clout whatsoever with drive manufacturers in
early 1978. What, some new fruit company in California? If anything,
Ohio Scientific had more clout with drive manufacturers, as they had
already been buying floppy drives since late 1976 and hard drives since
early 1977. (Apple didn't introduce a hard drive until late 1981.)
I imagine that by mid-1979 Apple was buying at least an order of
magnitude more floppy drives than Ohio Scientific, but it didn't start
out that way.
it was a win to be able to use a standard drive.
There's nothing that precludes using a clever controller design such as
Woz' Disk II controller with a standard drive. Apple using an SA390
rather than an SA400 was a cost reduction, but the basic Woz controller
concept can work fine with standard drives.
Also, I don't think there's any reason to think that Shugart wouldn't
have sold the SA390 to any OEM customer.
Eric
5:12 p.m.
Before OSI, AES was using a USRT as part of its floppy controller, as
did several other manufacturers (I think Zilog did also on the dev systems).
You could also occasionally run across Fairchild Macrologic CDC
generators in the old gear.
The big difference between the USRT-based and genuine floppy controllers
was the bit ordering within a byte.
The first WD floppy controllers were seriously expensive. Apparently,
initial yields on them were pretty low.
--Chuck
7 Jan
7 Jan
6:38 a.m.
On Saturday (01/05/2013 at 02:06AM -0800), r.stricklin wrote:
Howdy folks.
I have a handful of 5.25" floppy disks for an Ohio Scientific C1, which I would like
to image. Anyone have any info on this disk format, or know of a tool that can read them?
They don't appear to be in a WD177x-style format... at least not one intelligible to
ImageDisk or Tim Mann's catweasel tools. There is at least one C1 emulator out there
with support for disk image files, so I have some hope somebody's already done the
dirty work for me.
If nothing already exists, low-level info on the format would be awesome as then I'd
have something to work with, trying to extend Karsten Scheibler's catweasel tools.
A few cursory trudges through t3h Googles have borne little fruit so far.
I think you will find that the C1 used an async UART (MC6850) and a PIA
(MC6820) to interface to the floppy drives. The drives were typically MPI
(Control Data's disk division) drives that had the data separator built
onto the drive. Over the years there were lots of articles about building
improved data separators but I think the original async UART connecting
to the drive's READ and WRITE data paths remained the same design.
Weird / unique and definitely not compatible with any WD17xx format as
you mentioned.
There's good stuff here,
http://www.osiweb.org/
including schematics of the 470 floppy interface card that is probably the
origin of all of it,
http://www.osiweb.org/manuals/470.pdf
Chris
--
Chris Elmquist
8:22 a.m.
From: Chris Elmquist <chrise at pobox.com>
I think you will find that the C1 used an async UART
(MC6850) and a PIA
(MC6820) to interface to the floppy drives.?
Actually, the ACIA was used in synchronous mode, and the MFM encoding was derived from
both the clock and data signals.
Dave
8 Jan
8 Jan
4:46 a.m.
On Monday (01/07/2013 at 08:22AM -0800), Dave wrote:
From: Chris Elmquist <chrise at pobox.com>
The ACIA was run in divide-by-1, external clock mode, with the clock
being derived from the data using the clock extractor on the floppy drive
(originally) and other circuits over time. But it was still async,
with a start bit and 1 or 2 stop bits per byte.
The 6850 does not have a synchronous mode like a USART such as AMI
S2350, which has a true synchronous mode (can sync to a start byte per
frame rather than a start bit per byte) and was also popular in floppy
controllers such as the Heathkit H-17 and Percom LFD-400 for SS-50 bus
both 10-hole hard-sector, and all from about the same time.
Chris
--
Chris Elmquist
I think you will find that the C1 used an async
UART (MC6850) and a PIA
(MC6820) to interface to the floppy drives.?
Actually, the ACIA was used in synchronous mode, and the MFM encoding was derived from
both the clock and data signals.
4366
days inactive
4369
days old
7 comments
6 participants
participants (6)
-
bear＠typewritten.org -
cclist＠sydex.com -
chrise＠pobox.com -
dfnr2＠yahoo.com -
djg＠pdp8online.com -
eric＠brouhaha.com