I guess my question comes down to how compatible is the Cortex-M0+ to an UNO. I get conflicting info on web searches. I’m using the Arduino motor shield with the M0+ and it works fine. Since everything I’ve done is one way from the M0+ to the shield I guess that only means that the shield works well with the 3.3V signals. I’m also reading an IR sensor powered by 5 volts with the output of the sensor stepped down to 3.3V into an analog input. On a few web sites I’ve seen statements that the M0+ is actually 5V tolerant. I haven’t had the guts to chance frying the M0+ yet so I’m not sure how well that works. It would be nice to get rid of the extra circuit to step the voltage down if I don’t need it, so… Does anyone know what the real answer is? Is the M0+ 5V tolerant on the analog pins?