Richard Cini rich.cini at verizon.net
Sat Nov 30 20:15:14 CST 2019

    	The current P112 is a reissue from years ago, right? I remember I had one — and I may still have it somewhere — but I only used it with 3.5” drives. Somehow I think it was built that way by design (the board outline fit on a drive). 
I don’t know how available the code is, but I would look at the firmware on the board. To me it sounds like it has a bad drive definition. The 8272 is pretty easy to program for (I use it on my IMSAI). 
As an aside, I use a modified YD-380 (5.25” HD) drive to replace the 8” drives on my IMSAI so as a quick test you could use one of those. At least it can step to 80 tracks and has the same speed and bit rate. I have instructions on my site how to use it. 

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On Sat, Nov 30, 2019 at 8:42 PM -0500, "Bill Gunshannon via cctalk" <cctalk at classiccmp.org> wrote:

On 11/30/19 8:28 PM, Fred Cisin via cctalk wrote:
>>> A lot could depend on how the software is interpreting the FDC return
>>> codes.
>>> In the case of PC BIOS (765), error code number 4) that would mean that
> On Sun, 1 Dec 2019, Bill Gunshannon via cctalk wrote:
>> I think you missed something.  This is a P112 SBC not a PC.  I watch
>> the head step from track to track until it runs into the stop after
>> passing the last real track.  I have a dbit 8" adapter and it displays
>> the track count and I watch it go from 0 to 79.  I am assuming the
>> problem is that wherever the disk parameters are being stored on the
>> P112 they are wrong for 8" disks.
> That's exactly why I said that it depended on how the software 
> interprets error codes, and used PC as an eaxample for comparison, not 
> that it would necessarily be the same.
> You are absolutely right that I don't know anything about P112 disk access.

I was hoping there would  be people here who did.  I have had these
SBC's for several years but have never even powered one up before.

> You are right that the disk parameters are obviously wrong for 8", if 
> only the wrong track count.  I have seen THAT error before.
> Are the OTHER parameters at least usable?

I have no way of knowing.  My first test was to try formatting a disk
and then reading a (blank) directory.  But, as I said, while it says
the format was successful it can not read the disk.

> If it says "sector not found", then there is a possibility (LIKE the PC 
> example that I used), that that may mean that it sees sectors, but not 
> the right ones.  But, there is still the possibility that it is using 
> that message for any and all disk errors.

Again this is why I need to find someone with experience with the P112.
I am beginning to suspect these were not as popular in reality as they
seemed to be on mailing lists.

> BTW, I understand that NEC uses 77 tracks on their high density 5.25 and 
> 3.5 inch formats, and 360RPM for 3.5".   (Same parameters for all three 
> sizes!)

Well, I haven't tried 5.25" but 3.5" disks format/read/write just fine.


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