Date   : Thu, 17 Jun 2004 21:50:11 +0100 (BST)
From   : Greg Cook <debounce@...>
Subject: Re: Opus EDOS

In Message-Id <1086460513.1936.4.camel@...>
Jules Richardson wrote:
> There's an Alan Williams who posts to comp.sys.acorn.hardware -

I wrote to him, and he's not the author of EDOS...

But I did find the datasheet for the WD2791, which has an inverted data
bus and slight changes in the command set, compared to the newer WD1770. 
I have put up a table detailing the differences.  Otherwise the interfaces
of the two Opus boards are identical.

As for the ROM itself, inevitably Opus would have released firmware to
accompany the 2791 board, and no obvious third-party extensions appear in
EDOS.  In fact the 1770 was developed the same year as EDOS 0.4 and so
DDOS was the one that 'ported' to the new chip.  So the robustness of EDOS
and its similarity to Challenger were a red herring - but it reflects well
on Williams and Opus at that time.

The upshot of this research is that EDOS (and DDOS and Challenger,
presumably) turns out not to need a complex procedure to accept foreign
double density disc formats.  *OPT 6 has no effect here, but *CAT will
toggle the density flag for one drive, if no DFS or DDOS catalogue is
found.

Greg Cook
debounce@...
http://homepages.tesco.net/~rainstorm/

---

WD floppy drive controller table:
http://homepages.tesco.net/~rainstorm/fdc-combined.htm



       
       
               
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