Questions of Polarity and Enable

On Thu, 5 Dec 96 16:59:01 PST Zheng Shi of Symmetry wrote:

>Hi, Ibis folks:
>
>Can anyone tell me what the sub-param Polarity and Enable of
>keyword [Model] really means? Is Polarity used only on diff
>pins? Is Enable used only on tri-state pins? How can I decide
>the Polarity and Enable of an input or output pin?
>
>I can't find such detail information from IBIS2.1 Specification,
>can anyone give me some advices, or tell me where i can find
>the answer?
>
>Thanks a lot,
>
>-Zheng Shi
> zheng@symmetry.com
> Los Altos, CA.

     I belive the original intent was to support SSI logic components
(74OO series TTL and the like) by allowing the user to include
information on the outputs' logic operation. For example, the model provider
could specify if the the path from input to output was inverting or
non-inverting or if the enable on a tri-state output pin was high or
low. However, for a lot of components (microprocessors, PALS/FPGAS, RAMS,
etc.) these parameters don't seem to make much sense (to me, anyway). Unless
you were modeling an SSI component where this made since, I would
just default them to positive polarity and Active_high.

  Ibis old-timmers, any other comments?

               Best Regards,
               Stephen Peters
               Intel Corp.
Received on Fri Dec 6 14:42:44 1996