This diagram shows the various functional blocks of a UART peripheral found in the Silicon Labs C8051F900 family. There are two Special Function Registers (SFR) - SBUFx and SCONx – used to control and manage the serial communication. The UART peripheral is split between the transmit and receive sides. From the diagram it can be seen that the entire interface is driven by a separate block called the UART Baud Rate Generator. This is the internal clock source used to recover the received data as well as time the transmitted data output. Later slides will show how to set up the baud rates using the internal timers. The I/O is controlled via the crossbar, which is a special Silicon Labs feature that enables peripheral usage even on the smallest pin count devices by moving the pin assignments based on utilization. Lastly is the interrupt generation, which allows the CPU to be running other tasks while UART communications are active and only service the peripheral when the transmission is complete.