speaking of 3.5

[Allison]

melamy at earthlink.net wrote:
> I been "listening" to most of this thread so, forgive me if I already mention an idea that someone has already brought up...
>
> I seem to recollect that when I was working on hard sector floppy drives back in the Northstar Horizon system days, that the controller only wrote a block of data for each sector with basically nothing in between. It saw an index hole, wrote the block and then waited for the next index hole to write the next sector. If you want to recreate index holes for reading a hard sectored floppy, it seems you could detect the end of data from the previous sector and then generate a accurate index hole for the upcoming sector. Use the single index to reset the sector count if you are keeping track of that.
>   
You can also use index for the maker of start and just count off ten 
sectors at a 1/rotation rate.
Motor speed for a rotation is fairly stable but must be very close to 
speed as in less than a few percent.

However that will not help you read it on a modern floppy controller as 
the header and all the other marks
that FDCs (be they 765 based or  1771/1793 based) need to locate data 
are not there.

That said if your really out to read NS* disks the format and controller 
is fairly simple to subset
and build to be done off the parallel port of a PC for read only and 
maybe write.
This is possible as the controller for the S100 had to accommodate a 
slow 8080 or z80 (4mhz)
that would be pushing to write a byte every 64/32 uS and do housekeeping.

Of course having a real NS* is far more fun.

Allison
> Obviously, this is only a solution for reading the disk
>
>   
There are other solutions...


> best regards, Steve Thatcher
>
>   
>> Hi Chris
>> I was recently looking at my Teac drive's index pulse to see how it
>> worked relative to the drive going ready ( the problem of trying to
>> find a way to recreate the /Ready signal ).
>> One thing I noticed was that the leading edge of the index pulse
>> was as accurate as my scope could show but the trailing edge was
>> all over the place.
>> My thinking is that the drive is controlled by a servo loop.
>> The leading edge is when a crystal clock says the pulse is suppose
>> to start and the trailing edge is when the actual edge is detected.
>> If one timed the length of time between the two edges, one would
>> then know the corrective response of the loop.
>> As an example, if the pulse was long, you'd keep a similar software
>> wheel rotating that you apply a correction to by the amount the
>> pulse was long.
>> It would be this internal software generated wheel that you'd use
>> to create the index pulses from.
>> You need the code to watch the drive to determine the parameters
>> of the control system, gain, dampening and intertia.
>> If done this way, I suspect that one could get very close to
>> the right index pulse spacing.
>> Dwight
>>
>>
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