I am working on a project in which I am using a MKL03Z8VFG4 to periodically measure the output from a transistor amplifier. However, when initializing the ADC inputs, ADC_SE8 is always high. I also use ADC_SE9 which is at ground and works fine, as you would expect. They are both configured exactly the same.
The pin remains high whether the amplifier is connected or left floating, so it is not the external circuit.
I have checked that pull enable is off and pull select is low.
Would anyone be able to let me know why this might be happening?