If you drive a pin that’s already an output, for example, you could do real harm to the board. Because all the pins are shared, you have the same problem with the Arduino pins, too.

The whole thing worked because of all the generous people who have written Arduino code, and also code to adapt the basic Arduino stuff to work with alternative chips from the Microchip was Atmel) AVR ...

A Raspberry Pi Zero Shield that will connect a Zero or Zero W module to a 3.3V or 5V compatible Arduino board, is available from US-based Burgessworld Custom Electronics. The two boards are connected ...