pt100 is as far as I recall a thermocouple, so you must first amplify using a instrumentation amplifier then feed a a/d converter that feed your uC.

If you do not need more than 8 bit resolution (up to 12 bits if you can participate in the world layout championships) you can use a uC with built in a/d. DO remember that using a 24 bit a/d does NOT give you 24 bit precision.

Erik