[Coco] Re: Bellingham User Group Stuff

[Gene Heskett]

On Tuesday 03 February 2004 17:57, Boisy Pitre wrote:
>I suspect that bit 1 of byte $10 in LSN0 is not set. It should be,
>indicating to the driver that the disk is formatted as a 96tpi disk.
>
>Look at offset $10 of LSN0 of the disk image.  It should be $03, not
>$02.
>
>Boisy
>
That would depend on whether he wrote them to a 5.25", or to a 3.5" 
diskette.  The 3.5 was 135 tpi from the gitgo, so that bit should not 
be set for a 3.5" formatted disk as there is never a chance of a tpi 
miss-match there.

But since the 5.25" disk went through at least 2 commonly used 
trackspacings, setting that bit was a handy way to tell the driver to 
double-step a 96 tpi drive if it found itself reading a 48 tpi disk.  
Such a situation should result in the disk being write protected, but 
that was never written into cc(3)disk that I'm aware of, so the 
chance of trashing the disk with an inadvertant write is 100%.  The 
real problem being that the narrower heads in a 96 tpi drive do not 
erase the wider 48 tpi track well enough to be read by a wider 48 tpi 
head, often failing even in the same drive that did the errant write 
due to minor erros in head positioning, both from friction in the 
head carriage, and from play in the clamping rossette.

That write protection is something that really should be incorporated 
in the next generation of cc3disk.

>On Feb 3, 2004, at 4:10 PM, Bruce Calkins wrote:
>> O.K.?  I've downloaded these DSK images, changed the extension to
>> dot DSK,
>> Written them to 720k floppy disk with John Collyer's upgraded
>> DSKINI, and
>> tried to read them on my CoCo under OS-9.
>>
>> Result?  249 error - wrong type
>>
>> What's wrong?
>>
>> Bruce W.
>>
>>
>> --
>> Coco mailing list
>> Coco at maltedmedia.com
>> http://five.pairlist.net/mailman/listinfo/coco

-- 
Cheers, Gene
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Copyright 2004 by Maurice Eugene Heskett, all rights reserved.