In asynchronous serial communications, data is transmitted without the clock. Therefore, it is up the MCU to synchronize its internal baud rate clock to the incoming data. In the case of RS232, the start bit is used to start the process. The start bit tells the receiver the phase relationship required for the internal clock used to latch the data bits. The rate of this clock is typically determined at design time; however, there are some applications where devices are required to determine the baud rate from the incoming data stream. The example above shows one way for devices to align the internal clock with the incoming data. Once the start bit is received, the clock system restarts its count sequence, allowing for the clock edges to line up according to the bit time specified.