LVDS and terminators

Tak Asami asami at dt.wdc.com
Thu Oct 5 18:56:06 PDT 1995


Hi Skip:

Thank you for your commentary.

Well, I am not trying to be "wrapped up in the cost of technology", 
rather, I had a hidden agenda.

I openly asked the question, "what's the big deal about auto sensing
of the LVDS"?  Jim's reply was so that he can have an inventory of one
product that he can sell to either (SE or LVDS) market.
Well then, perhaps you didn't need the dynamic sensing of the LVDS.

Truth is, I wanted it, but didn't know if it was possible with the way
it is being defined in the draft document.

I was wondering what's limiting us from switching back and forth between 
SE and LVDS.  So a HBA can negotiate with each target to go LVDS during 
the data transfer, just like you negotiate synchronous transfer.  I think 
that's more useful, and we almost have all the hardware to do it.  
We will need a new message or twisting of an old message (like negotiage 
for 25nsec cycle and go LVDS).
This is only between the initiator and the target with a nexus.  No one
else need apply, and consequently, all arbitration and selection processes
are performed single ended.  Now that's a backward compatibility.

What's wrong with this picture?  I have some unanswered questions:
- Can someone implement a terminator that switches back and forth quickly
  between SE and LVDS mode by sensing the diffsens?
- Does switching SE to/from LVDS like that cause any electrical problems?

I think this is more useful and makes sense if the standard is put in 
place to enable this "interactive swithing between SE and LVDS".
But I didn't know if it was technically feasible, and didn't want to
discuss too openly until I have some more sense of it, plus if anyone is
really interested.
Anyone???
=========================================================================
                           Tak Asami
_|_|_|                     asami at dt.wdc.com
_|/ _| WESTERN DIGITAL     (714) 932-7621 : Voice
_|_|_|                     (714) 932-6496 : Fax




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