Computer network--synchronous and asynchronous communication "turn"

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serial communication represents its transmission rate at a baud rate, baud rate refers to the number of bits transmitted per second by the signal .

Serial communication includes two communication modes of asynchronous communication and synchronous communication .

　Asynchronous Communication represents the beginning of a character in a starting bit, with the stop bit representing its end. Its transmission format is shown in 8-1.

Figure 8-1 Format of asynchronous communication

As can be seen, the starting bit occupies 1 bits, the data is 5~8 bit, its length depends on the type of transmission data, first transmission low, after transmission high. After the data is a check bit, if set to parity , the number of data and check bit 1 is even. If set to odd check , the number of data and check bit 1 is odd. Finally, the stop bit, which can be set to 1-bit, 1-bit, or 2-bit as needed.

In asynchronous communication, the time taken by each bit is the reciprocal of the data transfer rate (baud rate). If the transmit baud rate is 2400, the time for each bit is 1/2400s, which is 0.416 Ms. If the transmission of an ASCII code, the data accounted for 7 bits, the starting bit, check bit, stop bit each accounted for 1 bits, the transmission of an ASCII code occupies 10 bits. With a baud rate of 2400, 240 ASCII codes can be transmitted per second. The common transmission baud rate for asynchronous communication is 150~38400.

When asynchronous communication is sent, the starting bit represents the beginning of the character, and the stop bit represents the end of the character. The receiving end uses these delimiters to transform a serial data into parallel data. This kind of communication is easy to implement, even if it is not sent continuously during transmission, it will not cause the problem of different steps. However, the transmission efficiency is reduced because each character is sent with two or three bits for synchronization.

Unlike asynchronous communication, synchronous communication sends a complete set of data at a time, and the two parties issue special synchronization symbols before sending. The transmission efficiency of synchronous communication is high, the communication coordination is more complex, and synchronization clock is required.

Computer network--synchronous and asynchronous communication "turn"