CompuPro floppy controller differences

Tony Duell ard at
Tue Sep 19 17:45:14 CDT 2006

> On Mon, 18 Sep 2006, Tony Duell wrote:
> > Rememebr the data rate of 8" SD is the same as that of 5.25" DD. I have
> > an idea the data separate _will_ lock to 8" SD (which is still 250kbps),
> > and you can then program the FDC chip to do single density operations. I
> > have never tried this, though.
> The IBM 5150 FDC board had NC to the FM (v MFM) pin on the 765,
> To program it to do "single density" would require that a little bit of
> that "programming" be done with solder.

Does it, though?

IIRC, that pin on the 765 is an output. So the 765 can be internally set 
to FM operation by sending it the right command bytes.

Now, the data separator should be able to lock to an 8" SD data stream. 
It's the same bit rate as the 6.25" DD data it's supposed to be working 
with. And just about any pulse sequence that an occur in an FM stream can 
also occur in an MFM stream. 

So the data seprate should lock and give out the 250kHz data clock and 
the data pulses. The 765 should be able to treat those as FM, single 
density recording. 


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