[IBIS-Users] Strange implications of ISSO_P* keywords

I was recently asked about IBIS and power-aware buffer modeling, but for *inputs*.



At present, IBIS supports two sets of keywords for power-aware modeling: [Composite Current] and [ISSO_PU]/[ISSO_PD].  [Composite Current] requires the presence of [Rising Waveform] and/or [Falling Waveform], which in turn require output Model_types, such as Output, Open_sink, etc.



However, there is no obvious requirement that [ISSO_PU]/[ISSO_PD] must be used with any particular Model_type at all.  While there are notes about using the keywords with ECL buffers, and recommendations about the Open_drain, etc. types, no other mention of Model_type is made for these keywords in the specification.



There are implications, though, in other language: the phrase "output transistors" is used, and there is no mention of Input or any I/O Model_type in the specification language for these keywords.



Realistically, we should be concerned about SSO effects on input buffers connected to supplies shared with multiple transitioning outputs.  Further, there's nothing in the time-dependent equations for the keywords that prevents the current distribution in the pullup and pulldown at an input from being calculated based on the V(t) of an incoming waveform at the pad.  Finally, the parser has no problem with Model_type Input being used with [ISSO_PU] and [ISSO_PD].



Is there any reason why ISSO_P* cannot be used for input buffers?



-          MM








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