Re: Questions about Submodels

Stephen:

My responses are in your text.

Bob Ross
Mentor Graphics

Stephen Nolan wrote:
>
> Hi IBIS folks. I'm working on our procedures for creating IBIS models of devices
> with Bus Hold, and struggling through this section 6a on Submodels. Help.
>
> First of all, are submodels a section that is entirely contained within a model
> section, or are they independant and inheritable by other models? For example,
> if I have an input model:
>
> |******************************************************************************
> [Model] LVTH244_DATAIN_33
> Model_type Input
> Vinl = 0.8V
> Vinh = 2.0V
> C_comp 3.35pF NA NA
> |
> [Add Submodel]
> BUS_HOLD_33 Non-Driving
> |
> |******************************************************************************
>
> Does the submodel BUS_HOLD_33 have to follow the data in the LVTH244_DATAIN_33
> model and be within that model, or can all of the submodels be at the end of a
> file in a separate section following the models?

It can be in a separate section.

>
> Further, once I have declared a "[Submodel] BUS_HOLD_33" submodel within the
> LVTH244_DATA_IN_33 model, do I have to include the complete submodel again
> within the LVTH244_OE_IN_33 model, or can I just simply call it and expect the
> simulator to use it. If submodels do in fact turn out to be local instead of
> global and inheritable, is there any namespace conflict?

They are global, so there is no namespace conflict.

>
> Next is the question of data extraction for bus-hold. The clamp curves in the
> main model contain all of the data on the VI characteristics of the bus
> hold-circuitry. See the attached pdf file for an example. What is the purpose of
> the trigger and pullup/down data in the submodel section? What information does
> it provide that is not already available in the clamp curves of the main model?
> How do you extract the Ramp data (test setup).

The clamp information is in addition to the bus hold operation. The clamp
tables should have 0 current in the normal operating regions (between 0 and
Vcc).
The Bus Hold circuitry which are really weak, triggered flip-flops are what
the submodel models. The advantage of the submodel approach is that the
dynamic effects of the Bus Hold circuit are simulated. The clamp approach
would capture only a static (DC) characteristic and assume instantenous
Bus Hold Operation.

The Bus_hold operation can also be used for dynamic terminations. That is
the main motivation for adding this to IBIS.

>
> Finally, in the spec there is the following sentence:
> > | The [Pullup] and [Pulldown] tables both are used to define an internal
> > | buffer that is triggered switch to its opposite state.
> What does this mean and is this sentence grammatically correct? I can't figure
> it out.

It should read:
| The [Pullup] and [Pulldown] tables both are used to define an internal
| buffer that is triggered "to" switch to its opposite state.

>
> Thanks.
> --
> Regards,
> Stephen M. Nolan
>
> --------------------------------------------------------------------------------
> Name: busholdcurves.pdf
> busholdcurves.pdf Type: Portable Document Format (application/pdf)
> Encoding: base64
Received on Thu Jul 20 18:02:50 2000