Quick reference for the RP2
    https://docs.micropython.org/en/latest/rp2/quickref.html
    
    UART (serial bus)
    There are two UARTs, UART0 and UART1. UART0 can be mapped to GPIO 0/1, 12/13 and 16/17, and UART1 to GPIO 4/5 and 8/9.
    
    from machine import UART, Pin
    uart1 = UART(1, baudrate=9600, tx=Pin(4), rx=Pin(5))
    uart1.write('hello')  # write 5 bytes
    uart1.read(5)         # read up to 5 bytes
    
    ----
    
    class UART – duplex serial communication bus
    https://docs.micropython.org/en/latest/library/machine.UART.html#machine-uart
    
    UART implements the standard UART/USART duplex serial communications protocol. At the physical level it consists of 2 lines: RX and TX. 
    
    UART objects can be created and initialised using:
    from machine import UART
    uart = UART(1, 9600)                         # init with given baudrate
    uart.init(9600, bits=8, parity=None, stop=1) # init with given parameters
    
    A UART object acts like a stream object and reading and writing is done using the standard stream methods:
    uart.read(10)       # read 10 characters, returns a bytes object
    uart.read()         # read all available characters
    uart.readline()     # read a line
    uart.readinto(buf)  # read and store into the given buffer
    uart.write('abc')   # write the 3 characters
    
    Constructors
    classmachine.UART(id, ...)
    
    Methods
    UART.init(baudrate=9600, bits=8, parity=None, stop=1, *, ...)
    tx specifies the TX pin to use.
    rx specifies the RX pin to use.