ibis usage for timing diagrams

My understanding is that ibis is used to determine flight time information. I am trying to perform an analysis of two IC's. For the sake of this question, lets take a pin that is bi-directional on each IC. Each datasheet specifies a "clk to valid."

One gives a value and condition of 20pF, with no additional information.

The other gives an "at the pin" value with conditions of purely resistive 50ohm load. They also say that the value is from 2.4V to 0.8V (which isn't going to happen with a 50 ohm load).

1. Should I be able to verify a value given in the data sheet with the ibis model? I have tried each and neither come close to the value in the spec. What about all of the parameters that are not given in the data sheet? I can assign values of Xo, propagation velocity, and delay.

2. How does the ibis simulation fit into a timing diagram? I assume there will be a base value, say "clk to valid" to which I will add the flight time given by the simulation. Is this the correct way to look at it? If so, what do I do about the different conditions listed above (20pF vs 50ohm)?

 
Received on Tue Mar 20 12:46:31 2001