[Coco] Read Coco floppies in my PC

[gene heskett]

On Sunday, April 01, 2012 03:33:10 AM John Kent did opine:

> I thought there was a reduce write current signal on some of the drives.
> Does anyone know how that was used ?

That RWC was used in some of the early drives to adjust the write current 
downward on the inner tracks of the disk.  The advent of better heads on 
most of the post Texas Peripheral era drives relegated that to the dustbin 
of time.

> I remember writing to some high density 1.2MByte floppies but could not
> erase them.
> 
> I have some WD279X chips. If you run them with a 2.4MHz clock in 8" mode
> perhaps they could be used to write high density 1.2MB drives. You'd
> have to build a 6809 board or wire wrap something.

I don't know if it works with all WD chips, but I have heard it works well 
with the Fujitsu MB8877 FDC, which I believe was cmos where the WD of the 
day were nmos.  I believe it is known not to work with the OEM WD277x 
FDC's.  If one could find WD 277X's that were made in the later 90's, I 
suspect they would work since production improvements (read "die shrinks") 
would have maintained the specs while reducing power input and increasing 
the speed of the logic at the same time. Finding that out might be an 
interesting exercise, but with DW making floppies about 95% obsolete, it 
isn't an experiment I'd personally feel like doing.
 
> John.
> 
> On 1/04/2012 6:34 AM, Frank Pittel wrote:
> > I remember back in the day when there was a lot of talk about the
> > problem that never had any issues with it on my computer. It had a
> > 360K drive and a 1.2 meg drive and the 360K drive never had a prob
> > reading disks written by the 1.2meg drive.

I wonder if some of those 1.2 meg drives were actually being speed 
controlled from the PC with the RWC signal?  That method of reducing its 
spindle speed to 300 rpms, combined with double stepping, could have 
written a 48tpi disk (from a bulk erased disk) that would have been quite 
readable in the 300 rpm 360k disk drive.

Fairly easily checked if the 1.2 drive has a dual strobe pattern on the 
bottom of the spindle so you could tell 360 rpms from 300 rpms.

> > That of course was me and those two drives though! I make no claims
> > about other drive combos!! It's also been a long time since you've
> > used a floppy on anything but my coco and I'm moving towards
> > drivewire as fast as I can!!
> > 
> > The Other Frank

Cheers, Gene
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