Re: Drive-on-demand

D.C.:

Based on your description, I do not believe Bus_hold will work
directly. I do not believe simulators will work with
"negative" currents in the tables - meaning doing the
opposite of what is expected or creating a negative
impedance buffer that acts opposite of a conventional buffer.

Opposite polarity I-V tables will probably be flagged
as an error by the ibischk3 parser. Therefore it would
not be legal.

I cannot think of any clever alternative with IBIS
Version 3.2.

However, I believe the new macro language under discussion by
the IBIS Futures Working Group will be able to handle this
situation (this would be a good test case).

Bob Ross
Mentor Graphics

"D.C. Sessions" wrote:
>
> Need to double-check this. It seems that there are standard
> logic components which, on output, sense the output voltage
> and adjust drive current in response.
>
> No, I don't mean bus hold. These parts drive LOW hard when
> the output voltage is above a certain threshold and cut the
> drive when the output is below that threshold. Rising-edge
> drive is similar.
>
> Yes, I know that this is of dubious stability. Nobody asked
> me if they should do it this way, but the manufacturers want
> to make this a JEDEC standard and I'm trying to help them
> put together an IBIS model. Which, as far as I can tell, is
> possible using
>
> Submodel_type Bus_hold
>
> and having negative currents in the [Pulldown] and [Pullup]
> tables.
>
> 1) Have I missed a better way to do this?
> 2) Will this be legal?
> 3) Will this break EDA tools?
>
> --
> D. C. Sessions
> ibis@lumbercartel.com
 
Received on Thu Aug 31 18:26:26 2000