I hope this is the proper place to post this questions. I tried NXP I2C fourm but it appears to be shut down (not working anymore) I have an I2C spec question. For fast-mode 400kHz the spec is confusing about the rise and fall time spec is there a minimum spec or not. Upper limit is clear at 300 ns but I have heard lower limit is 20 ns but not sure this is true. Also the I/O capacitance loading for measing rise and fall time is not clear either. Spec says 0.1 Cb were Cb is the total bus capacitance. a fully loaded bus is 400 pf so does that mean 40 pf is the loading for testing rise and fall time. Thanks for any help anyone can provide and if this is not the place for this question if you know where I can post this I would be happy to move it there.