The maximum clock frequency of the MSP430F123IDW is 16 MHz.
To use an external clock source, connect the external clock signal to the XIN pin and configure the UCSCTL4 register to select the external clock source.
The RST/NMI pin is a dual-function pin that can be used as either a reset input (RST) or a non-maskable interrupt (NMI) input.
To use the built-in UART, configure the UART module by setting the UCAxCTL0 and UCAxCTL1 registers, and then use the UART transmit and receive functions to send and receive data.
The power consumption of the MSP430F123IDW in low-power mode (LPM3) is approximately 0.5 μA.