Serial not working in its simplest form

Hello,

it depends on what version of the MbedOS you have in your project.
The Serial API is deprecated and can be used only in MbedOS < 6 for MbedOS =>6 there are new APIs BufferedSerial and UnbufferedSerial . On APIs pages you will also find a basic examples. With these new APIs you also can not use printf function. But you can still use it for a debugging .

BR, Jan