The [AM1808 SoC](EV3 Processor) has 3 UART controllers. We are also using the [PRU](EV3 PRU) to provide 2 additional UARTs.
##Usage UART0: Input port 2 UART sensors.
UART1: Input port 1 UART sensors. Also debugging terminal (starts at boot).
UART2: Bluetooth.
SUART0?: Input port 4 UART sensors?
SUART1?: Input port 3 UART sensors?