[Coco] Coco 3 high-density floppy controller/IDE interface

[Phill Harvey-Smith]

Gene Heskett wrote:
> On Thursday 03 July 2008, David Hazelton wrote:
> What does it do with the 3rd ds line?  That was not normally the fdc's 
> responsibility, but was selected via separate latching buffers on the 
> controller pcb.  There were times I had considered replacing the 3 DS lines by 
> feeding them to a 3x8 decoder to get 8 drives & then I wouldn't be moving drive 
> cables all the time to switch from the various flavors of 5.25" drives to the 
> 3.5".

Looking at the schematics in Eagle, and the data sheet for the Intel 
FDC. The FDC supports up to 4 drives, but as the interface is wired up 
for connection to standard PC type floppies, the DS2/3, and ME2/3 lines 
are not connected to the drive chain. However it would be possible to 
connect these so that 4 drives could be supported. Connecting the DS0..3 
  direct to the interface and the ME0..3 through some logic to the 
/MOTOR line. OK this would break compatibility with IBM drives, but 
would allow for up to 4 drives, and IBM drives could still be used with 
apropreate cable twists :)

Another solution may be 2 IBM compatible drive connectors that differ 
just by which DS/ME combinations they have routed to them, so you would 
keep the current one, and add another with DS/ME 2..3 routed to it, 
though I'm not sure if this would work due to it effectivly being a Y 
shaped cable with the controler in the middle.

Cheers.

Phill.

-- 
Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !

"You can twist perceptions, but reality won't budge" -- Rush.