[sebhc] hard sector substitute

Steve Thatcher melamy at earthlink.net
Wed Jun 30 08:58:57 CDT 2004

Hi Dave, only drives that had been accessed recently would be on for a default time. If you didn't access it again within a second or two then the drive would deselect internally. If you are copying disks, then both being on wouldn't be that unexpected.

If you are writing on a drive, the main system will still deselect the drive and the write gate would already be turned off from writing the last sector.

Good idea about the disk drive wheel. I had forgotten about that and it would be a "fine" encoder for giving speed feedback.

As for waiting for the index hole, a drive controller would be forced to wait for the main index hole anyway to then count the index holes to the correct sector to read or write. There would be no inaccuracy on the main index hole and then an acculative effect on the rest of the holes if there was no speed feedback until the main index hole came around again.

best regards, Steve

-----Original Message-----
From: Dave Dunfield <dave04a at dunfield.com>
Sent: Jun 30, 2004 8:51 AM
To: sebhc at sebhc.org
Subject: Re: [sebhc] hard sector substitute

At 08:14 30/06/2004 -0400, you wrote:
>Hi Dave, I was not contemplating modification of the drives and I also wanted to make the device work on any hard sector system. N* uses HS and not HM for example (I have both N* and H88 systems...).
>best regards, Steve Thatcher

Hi Steve,

Understood - my point is that I think it would work better if yo do
modify the drives - Perhaps this can be "faked" by externally gating
all the drive signals, however I anticipate problems in switching
to and from writing selected to "deselected", and you also have the
interesting "feature" that all drive select LED's would be on at
once! - but it may be feasable.

Here's another intesting idea - many drives have strobe disks for
adjusting the speed - this could be used to "read" the drive speed
optically, and therefore you could know exactly how often to
inject the extra pulses - you still have the sync problem with the
main index hole, but it would solve the problem of having to wait
for it twice to obtain exact drive speed. It would mean that your
adapter card would need a little sensor mounted under the drive

dave04a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools: www.dunfield.com
com             Vintage computing equipment collector.

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