Grrr - !%#*^@# Kaypro! - test-drb@ccmp.vtda.org

4 Aug 2005

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Subject: Re: Grrr - !%#*^@# Kaypro!
   From: Dave Dunfield <dave04a at dunfield.com>
   Date: Wed, 03 Aug 2005 22:58:25 -0400
     To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>

    ???!  The value for R must be a valid sector number. 
For floppies
 that is never zero. There are a lot of floppies with sector numbers starting with
0.
765 can read them and write them. 
Maybe... there are caveats on that.  Technically a sector number of 0
should not be used.

Did a lot of work at "NEC"  (US arm then was NEC Micromputers USA, then later 
NEC Electronics USA.) in the early years when they were developing and 
marketing that and a HDC.  I was on the hardware/technical side. 
When I designed the 765 based disk system in my D6809/CUBIX system, I "didn't
know better" and numbered the sectors within a track from zero - this would
have been early to mid 80's.

Never changed it, as it has never caused a problem - versions of this system
were built with both NEC and Intel (8272) controllers, and used for many years.

ImageDisk reads and recreates CUBIX disks with no problems.

I cannot find any information in the NEC data sheet which describes any
restriction on the sector number (other than that it is one byte) - can you
provide a reference to these caveats? this is the first I've heard of them. 

Yes, NEC never guarenteed that it would work or continue to work.  There were
a few chips used in PCs (Not fully 765 compatable) that were questionable 
around this.

I also tried it and found it worked. However IBM 3740 and later Floppy specs 
had reasons for not using 0th sector.   As they say by spec it's wrong 
otherwise it works.

Allison