Why is the Bus Speed I measured so far off from the setting I chose? There was a typo in the Manual for PC-I2C-DEV. If your Developer's Manual is version 3.0 or 3.1 then the following change needs to be made. On page 6, the description of the parameter "n50Percent" "Half of the desired clock period in uSec" This should be: "Fifty times the desired clock period in uSec"