I have flashed the latest Marlin firmware (2.1.2.1) with config files from the examples directory for this BTT board. The status light changes from fast to slow blinking, but there is no communication over the serial port to the host PC. I have spent hours searching forums and the web for an answer, but have not really found it. I have checked and re-checked the config files to make sure the board and comm settings are correct. Any suggestions would be appreciated.