In SPI master mode, communication as fast as 4Mbps is possible, and in 
UART mode up to 2Mbps. The USART can be configured for both synchronous 
(SPI) and asynchronous(UART) operation and can select from several 
internal and an external clock source which are independent of the CPU
clock. In SPI master mode, the USART can operate as fast as 1/2 of the 
applied clock. For example if an 8MHz clock is used, 4Mbps transfer is 
possible for the SPI master. In the UART mode, at least 3 or 4 clocks per 
bit are required for reliable communication. For example, using a 8MHz 
clock divided by 4 supports up to 2Mbps. A complete description of the 
USART capabilities is provided in the MSP430xxxx User`s Guides available 
at www.ti.com/msp430.