How to connect Raspberry Pi 3 and FPGA cylone IV E Altera for Uart communication

Question

I'm trying to connect Raspberry Pi 3 and FPGA for UART communication. I connected directly two pins of my FPGA to the rx and tx pins of my Raspberry Pi 3. However, the data received by Raspberry Pi is not the data sent by FPGA. In simulation everything works fine. What is happening? Is something with the connection?

Answer 1

Make sure both devices have the same ground as reference. You can either achieve this by shorting the ground pins on both devices or connecting them to the same power supply.

Without a common reference, what is a high value for the FPGA might be interpreted as a low value by the Raspberry Pi because it doesn't "know" what to compare it to.