[sebhc] Heath Hardsector disks

[Dave Dunfield]

>I recall an article (possibly Sextant about 1985) about a hardware mod to
>the heath drives allowing them to read soft sectored media. I'm kinda rusty
>on this but it seems the heath disks had 10 holes, 9 equally spaced and one
>of which was half spaced between. The hardware generated the pseudo holes by
>some sort of multi-vibrator timed off the single hole. Does that ring a bell
>with anyone? Roger B.

I've thought about building a little micro (PIC or AVRish) to do this. The
only problem I see is that you cannot begin inserting the hard-sector pulses
until slightly more than one revolution of the disk - at least on the very
first access after power-on - once you have achieved the first calibration,
you can remember the timing for subsequent accesses, however you still can't
insert the hard sectors until the index pulse comes along.

The reasons I think it's worth using a tiny micro are that it would be very
easy to do these things:

 - Have a guard time so that if the initial index pulse comes too soon after
   motor-on, you can ignore it and wait for the next one - this insures that
   the drive is up to speed before you begin timing/inserting pulses.

 - "Remember" the timing for up to four drives, so that after the first
   calibration (power on), you can begin inserting hard-sector pulses as soon
   as you see the index pulse (subject to above guard time of course).

 - Constantly check and adjust the insertion time based on the total track
   time on a per-drive basis - this should make the unit very accurate, which
   I believe will be required for reliable operation.

 - Auto-detect soft/hard sectored disks, so that either one can be used
   without any special concern by the operator.

It shouldn't be too hard to build a very small board which goes between the
controller and the drive cables and can handle all of the drives (with a
single board).

Unfortunately I still haven't found an H17 - however if I ever do, I will
most likely design and build such an adapter ... Anyone got an H17 to spare?

Regards,
Dave
-- 
dave04a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools: www.dunfield.com
com             Collector of vintage computing equipment:
                http://www.parse.com/~ddunfield/museum/index.html


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