I use the Open Source Documented Verilog UART by Timothy Goddard. It is MIT licensed.
The source code on github and opencores.org.
Make sure the serial port settings are correct.
Use the terminal program PuTTY.
- Micro-UART by Jeung Joon Lee, 4/27/2001 (Verilog): Source code, manual
- LatticeSemi (VHDL)

