Coco FDC hacks (was: Ebay reaches new low

From: Fred Cisin <>
Date: Tue Nov 9 19:01:24 1999

On Tue, 9 Nov 1999, Roger Merchberger wrote:
> >My recollection was that there were several different vartieties. Each
> >one will have slightly different issues.
> Hmmmm... Looks like I need to grab the controller catalog # (and other
> specifics) and keep it in my Palm...
They almost certainly all had the same RS catalog # :-(. I'm not the
right person to ask. Better to check with somebody familiar with the
various RS variants, such as Dr. Marty <>.

> >To add 3.5" HD floppies, you will need to provide a different clock, way
> >to change it back and forth, and support for one more signal to the drive.
> I know you need a different clock (500Khz signaling rate vs. 250Khz for
> double-density) but I'd like to know if it's as simple as a DPDT switch &
> another crystal, or are there more things to keep a lookout on (like
> different buffers, software changes WRT timing issues, stuff like that...).

Rather than a switch, you'd probably want to control it in software, so as
to retain full low density DD capability. First step would be to find out
if others have been there before. If not, check with Allison about
whether the rest of the RS Coco FDC cartridge circuitry can properly
handle the higher speed.

> >Why do you want to run more than one FDC? If it is to run 4 instead of 2
> >drives, you can do that with minor hardware and software hacks to a
> >controller.
> Well, IIRC the most drives you can hang off of one controller is 4 SSDD
> drives, or 3 DSDD drives because the Side Select signal was used for one of
> the drive select pins. (Again, I think... If I'm wrong, please enlighten
> me.)
That sounds about right to me.
> I was looking to hang 3 DSDD & 3 DSHD drives off my CoCo... purely for
> shits & giggles. If it's a ton of hardware work, "nevermind" comes to mind.
> However, if it's some hardware & hacking some device drivers, then... I've
> always wanted to hack around with the device drivers of OS-9... :-)

Easiest way would probably be to use one controller, and rig up a software
controlled switch to go between two cables. Otherwise, you run into
issues of whether the Coco used memory mapped IO, modifying second
controller to function at a different address, and writing new drivers.

Once you add the other clock circuitry, be sure to write a driver to do 8"

Somebody ELSE will probably know whether it has been done before.

Grumpy Ol' Fred
Received on Tue Nov 09 1999 - 19:01:24 GMT

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