Date   : Fri, 12 Jan 2007 14:14:10 +0000
From   : adsb@... (Andrew Benham)
Subject: ADFS and DFS in a beeb

Jules Richardson wrote:

> Next question: apparently an 8271 *won't* work, which unfortunately is what's 
> in the 'desktop' beeb...

If you want access to ADFS floppies, the 8271 isn't what you need - it
doesn't do double density.  With an 8271, you can access an ADFS winchester
but not ADFS floppies.

> What about a 1772? That's what the "nearest" other beeb has - it's a 28 pin 
> chip on a small adapter board along with three LS logic chips, plugged into 
> the normal FDC socket on the beeb. Is it 1770-compatible?

1772 is the same as a 1770, but with different step rates.  You get to
choose one of 4 (I think) step rates in the command, and the 1772 has
different values from the 1770.  I think the 1772 was used in Master
Compacts and Archimedeseseses.

> The other obvious question is whether Watford's DFS is compatible with the 
> 1770 chip? (or the 1772)

Only if you've got the 1770 version of Watford's DFS...

Watford also did a DDFS, which is only for a 1770 and supports double density
(18 sectors of 256 bytes) for DFS.  I must have a copy somewhere, because I
hacked it to work on the BBC Master.

-- 
Andrew Benham           adsb@...       
Southgate, London N14, United Kingdom

The gates in my computer are AND OR and NOT, not "Bill".