Hi,i am testing the i2c function of my uno r4 minima, but i feel really confused because when i used usb-c to power the board, i2c works well but if with a 9V Battery, i2c stopped. I tested the normal Uno, it has no such problem. The other function of r4 is fine. Do you have some ideas? Thanks!
Welcome to the forum
Have you tried measuring the battery voltage when powering the board ? If it is a PP3 battery then it is likely that it cannot supply the required current to power the board