Introduction - If you have any usage issues, please Google them yourself
Echo a received character, RX ISR used. Normal mode is LPM0.
USCI_A0 RX interrupt triggers TX Echo.
Baud rate divider with 1MHz = 1MHz/19200 = ~52.1
ACLK = n/a, MCLK = SMCLK = CALxxx_1MHZ = 1MHz