🚀 go-pugleaf

On Tue, 24 Feb 2009 17:43:49 +1100, "gcd"
<gcdmelbnospam@deletemelbnospam.iimetro.com.au> put finger to keyboard
and composed:

>I've had some success using a standard pc drive. Had to use DS0 rather than 
>DS1 (expected)  and needed to ensure the drive was using disk change on pin 
>34. The only thing that is still a little peculiar is the density select and 
>whether it's an input/output or both. Using a standard PC drive I need to 
>use a HD disk but cover over the HD hole and that seems to work reliably. On 
>the original drive I would use HD without covering up the hole. The only 
>issues I end up with is that the drive light is always 1/2 on when not in 
>use.
>
>I'll keep looking for FD-235GF data and playing around. i'ts almost sorted 
>now
>
>Thanks
>Greg

This URL suggests that pin 2 is an input to the drive:
http://pinouts.ru/Storage/InternalDisk_pinout.shtml

I suggest you look at the datasheet for an old multi-IO chip such as
were used on 486 and Pentium motherboards, before the functions were
incorporated into the chipset.

For example, here is the datasheet for a Winbond W83757F:
http://www.datasheetarchive.com/datasheets/Datasheet-022/DSA00379504.pdf

Amongst the FDC pins is RWC, Reduced Write Current. "This signal can
be used on two-speed disk drives to select the transfer rate."

 Logic 0 = 250 Kb/s
 Logic 1 = 500 Kb/s

It is described as an "open-drain output pin with 24 mA sink
capability".

I've seen this pin used in 2-speed 5.25" drives, but not in 3.5"
drives. It could be that the HD hole in the diskette tells the [PC]
drive what write current to use, but the drive does not report the
diskette type to the controller.

Does your Advantest network analyser write 1.44MB or 720KB of data to
the diskettes? It would seem odd if the drive were writing to the
diskette as if it were a 720KB lo-den type while the controller were
transferring data at a hi-den (500 Kb/s) rate.

Could it be that your current setup is operating at a 250Kb/s data
rate, and that your diskette's capacity is being reduced to 720KB?
Could it be that the original FDD uses the "RWC" pin as an output
rather than an input, and that it communicates the diskette type to
the analyser, in which case the analyser could automatically adjust
the data rate to suit??? In the latter case, if the analyser doesn't
get any feedback from the drive, perhaps it defaults to a lo-den data
rate. You might like to experiment with a pull-down or pullup resistor
on this pin.

- Franc Zabkar
-- 
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