Re: Reading Commodore 900 disks in the 8250 (LP)

Commodore 900 Floppy Di8/c
1. System Overview
...
The data storage method used today is
GCR ( Group Coded Recording ). The subsystem supports the later addition of
hardware and software for the MFM format. The floppy drive is a 96 TPI
(tracks-per-inch) mechanism.

On Thu, Jan 11, 2024 at 8:17 AM Santo Nucifora <santo.nucifora_at_gmail.com>
wrote:

> It's 80 tracks according to the C900 Floppy Specifications document where
> it talks about the number of sectors per track.  Document is here:
> https://vintagecomputer.ca/files/Commodore/C900/C900%20Floppy%20Specification.pdf
>
> Santo
>
> On Thu, Jan 11, 2024 at 8:10 AM Francesco Messineo <
> francesco.messineo_at_gmail.com> wrote:
>
>> On Thu, Jan 11, 2024 at 2:03 PM Francesco Messineo
>> <francesco.messineo_at_gmail.com> wrote:
>> >
>> > On Thu, Jan 11, 2024 at 1:58 PM Santo Nucifora <
>> santo.nucifora_at_gmail.com> wrote:
>> > >
>> > > Just to clarify:
>> > >
>> > > The 8250/SFD-1001 uses a Matsushita JU-570 or JU-570-2 drive mech.
>> The C900 uses a JA-560-012 drive mech and the serial number on mine is in
>> the 100s.  I have never seen another drive in the wild.  Other than the
>> C900 documentation, I have not been able to find any other info on these
>> drives.
>> >
>> > according to this document:
>> >
>> https://retrocmp.de/fdd/panasonic/Panasonic_JU-475-4_Service_Manual_OCR.pdf
>> > The JA-560 is a 96 TPI drive
>> Ok maybe this can be indeed a too quick conclusion, the -012
>> additional part number may indicate a different head actuator that
>> makes it a 100 TPI drive. Indeed there seems to be no documentation
>> about these drives. I would just try to find information about the
>> disk format, 80 VS 77 tracks would clarify the issue.
>> Frank
>>
>>