[IBIS-Users] Combined Pulldown and Pullup warnings when using parse 4.0

IBIS-users,

I am responsible for creating models for my company's precision mixed signal devices. I create these models through the IC spice simulations and I use the three corners for my simulation (power, voltage, process). Once I convert the spice data to IBIS I occasionally get these warnings from the 4.0 parse:

WARNING - Combined Pulldown for Model: GPIO Typical data is non-monotonic
WARNING - Combined Pulldown for Model: GPIO Minimum data is non-monotonic
WARNING - Combined Pulldown for Model: GPIO Maximum data is non-monotonic
WARNING - Combined Pullup for Model: GPIO Maximum data is non-monotonic

When I view the data graphically, I am unable to see the point where this warning is generated. I assume that this warning is referring to the calculated summation of the pulldown (or pullup) data, ground clamp, and power clamp data.

My questions are:
1. How do I identify the region(s) where this monotonicity problem is occurring?
2. What corrective action can I take to remove these warnings?
3. What impact will this monotonicity problem have on my customers as they use this IBIS model into their simulations?
4. Will this warning cause problems in some or all of the EDA platforms that simulate IBIS circuits?

Another issue with these warnings is, I sometimes have a "good" file without errors but when I go back to the buffers in the file and correct the I-V/V-t mismatches these types of warnings are generated. Once again, graphical inspection does not help in identifying the point where these warning are generated . My questions for this issue are:
1. Do I go back to my original "good" file and discard the I-V/V-t corrections?
2. How do I identify the region(s) where this monotonicity problem is occurring?
3. What corrective action can I take to remove these warnings?

Best Regards,

Bonnie Baker
Texas Instruments, Tucson

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