We are using the KL27Z256VFT4 in a project currently in development. It seems that the VREFH cannot be used with an external reference. When attempting to use a 2.5 volt reference connected to VREFH the adc conversion consistently reads 0xFF. I have verified that the internal reference is off and that the source for the ADC reference is set to the VREFH/VREFL pair. Is there something I am missing?