Date   : Wed, 25 Feb 2004 14:00:31 +0100 (GMT)
From   : Johan Heuseveldt <johan@...>
Subject: Re: IDE Interface for BBC

Hi, Jonathan,

On Wed 25 Feb, Jonathan Graham Harston wrote:
> Johan Heuseveldt <johan@...> wrote:
> > On Mon 23 Feb, Jonathan Graham Harston wrote:
> > > I've updated the circuit diagram at
> > > http://www.mdfs.net/Info/Comp/BBC/Hardware/IDE/8bitcd.gif
> > 
> > That link doesn't work. Went back one level and found '8bitcdv1/gif'.
> > That's the one you had in mind I suppose?
>  
> No. It's definately 8bitcd.gif 8bitcdv1.gif is the former version 1
> diagram.  The updated diagram should say "R/W clocked via 74ls139" at the
> bottom.  Try doing a forced refresh - Shift-Refresh on most browsers.

I'll check again. Thanks.

> > If not already known, visit:
> >   <http://www.t13.org/>
> >   Technical Committee T13 AT Attachment
>  
> Been there, got the 2.5" stack of technical printout!

OK. :-)

But am I otherwise ignored?
Don't know how to interpret your silence on my comments.

Perhaps I'm being hard headed:

Look in the ATA-2 document at page 73 for the diagram, and 74 for the
values. The top two signals are relevant - in this context - with t1 as the
vital timing parameter, which is a minimum. Depending on the mode 0, 1 or 2,
the minimum setup time in ns is 70, 50 or 30 respectively. That's the minimum
time CS must be stable when asserted before the RD and WR strobes may
change to their asserted state.

Also, you need to know in which one of the three modes (0,1,2) is coming
alive when powered on. If you don't know (no specs available) you should
assume the worst, which is mode 0, needing the slowest/longest setup time of
70 ns! The design should address that.

Using a cleanup circuit, all signals - CS, RD and WR - are there almost at
the same time, except for some propagation delays of gates and FF. Thereby
also using nothing of the time you are offered in clock phase 1, giving a max
of 500 ns in which everything has to be done. The slowest mode 0 needs at
least 600 ns! That's what is wrong!

Have fun!

greetings,
Johan

-- 
Johan Heuseveldt <johan@...              >
  aka  waarland

  The best place is a Riscy place
 
I'd rather have a free bottle in front
of me than a prefrontal lobotomy.