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Serial communication is to convert the parallel data to be transmitted inside the computer into serial data and transmit it through a communication line; then convert the received serial data into parallel data and send it to the computer. Before the computer serially sends data, the parallel data inside the computer is sent to the shift register and shifted out bit by bit, converting the parallel data into serial data. As shown below
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When receiving data, the serial data from the communication line is sent to the shift register, and after being shifted and saved to 8 bits, it is sent to the computer in parallel
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1.3 Data sampling
When the receiver receives data, the internal clock frequency of the UART is often higher than the external data input frequency. When the receiver starts to receive the signal, if the frequency of the internal clock is close to or less than the external data transmission frequency, when the receiver receives data, it is likely that the data will not be collected at the edge of data sampling, or the wrong data will be collected. The sampling frequency can be set to 8 times, 16 times the external data transmission frequency. The UART uses 16 times the external clock frequency, and the sampled waveforms are as follows:
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