While setting up my Rpi3 + GrovePi+ setup for serial communication, I have enabled UART and disabled the console, and I am testing by connecting the RX pin on the GrovePi’s GPIO header to the TX pin next to it. When I connect to it using screen or minicom at 19200 bd, I am getting a jumble of garbage characters. The expected output should be an exact echo of the input characters. This also happens when I do the same loopback using a connector connected to the RPISER port on the GrovePi.
When I test with a serial device (for example, the RockBlock Mk2 I am trying to attach) I get similar results.
When I remove the GrovePi hat, and create the loopback between the RX and TX pins on the base Rpi3, everything works fine.