I have been trying to get two FRDM K64f boards to communicate using UART3 through pins PTC16 and PTC17. I have been using the uart_interrupt_polling example from KSDK, but I'm not receiving anything. I've changed the code to use UART3, and one of the boards is sending at first, while the other is receiving. I've tried connecting matching pins and crossing the pins. Is there a setting I'm missing or another hardware connection I need to make?