Switched clamping diodes

All,

Thanks to everyone who replied to my earlier mail to ibis-users.

>From the answers, I don't think my 2nd point was
expressed clearly enough

> 2) One family of components switches out the power clamp
> diode whenever the output buffer is in tri-state.

This family is 5V tolerant LVC from Philips (and TI). When in
3-state, the clamping diode to Vcc is "removed". However, in
active state, it is present.

In the IBIS spec, it is assumed that:
   "the data in the clamping curve sections are handled
    as constantly present curves and the pullup and
    pulldown curves are used only when needed"

This assumption is false for LVC. The clamping curves are not
constantly present!

A work-around for 2.1 is to put the clamping curve in with the
pull-up and pull-down curves. As long as the 3-state curve is
truly high-impedance, the model will be very good.

For 3.0, perhaps it would it be an idea to have separate curves
for active and 3-state modes?

2.1
       3-state: [3-state] = [GND_clamp] + [POWER_Clamp]
        Active: ( [Pullup] or [Pulldown] ) + [3-state]

3.0 Proposal:
       3-state: [3-state] = [GND_clamp] + [POWER_Clamp]
        Active: [Pullup] or [Pulldown]

In order to reduce confusion, it would be better to rename
[GND_clamp] and [POWER_clamp] to [3-state pullup] and
[3-state pulldown]. Then, if the simulator detects the new keywords,
it will know that the definition of [Pullup] and [Pulldown]
has changed. In this way, a 2.1 description would still be valid
in 3.0.

Any comments?
John

-- 
John Fitzpatrick   <John.Fitzpatrick@ln.cit.alcatel.fr>    
Alcatel CIT, 4 rue de Broglie, 22304 Lannion, France
Tel: (+33)96.04.79.33  Fax: (+33)96.04.85.09