Serial communication and parallel communication
According to the way of data transmission, communication can be divided into serial communication and parallel communication. A communication method that transfers data bit by bit. Parallel communication generally refers to the communication method that uses 8, 16, 32, and 64 or more data lines for transmission. The comparison of their communication transmission is shown in the figure. Parallel communication is like a highway with multiple lanes, which can transmit multiple data lines at the same time. The data of one data bit, and the serial communication, and the serial communication is like the highway of a single lane, can only transmit the data of one data bit at the same time.
Obviously, because the data of multiple data bits can be transmitted at one time, the amount of data transmitted by parallel communication is much larger under the same data transmission rate, while serial communication can save the hardware cost of data lines (especially long-distance communication). distance) and the wiring area of the PCB, the comparison of the characteristics of serial communication and parallel communication is shown in the table.
Full-duplex, half-duplex and simplex communication
According to the direction of data communication, communication is divided into full-duplex, half-duplex and simplex communication, which are mainly distinguished by the direction of the channel, as shown in the figure and table.
Still using the road analogy, full-duplex communication is a two-way lane, and the traffic in the two directions is independent of each other; half-duplex is like a country road, only one car can pass at the same time, and traffic in the other direction can pass. Cars can only pass when the road is clear; a simplex is like a one-way street where vehicles in the other direction are completely closed to traffic.
Synchronous and Asynchronous Communication
According to the data synchronization method of communication, it is divided into two types: synchronous and asynchronous, which can be simply distinguished according to whether the clock signal is used in the communication process.
In synchronous communication, the two sides of the transceiver equipment will use a signal line to represent the clock signal, and the two sides will coordinate and synchronize data driven by the clock signal, as shown in the figure. In communication, both parties usually stipulate uniformly to sample the data line on the rising or falling edge of the clock signal.
In asynchronous communication, the clock signal is not used for data synchronization. They directly insert some synchronization signal bits in the data signal, or package the main data, and transmit the data in the format of data frame, as shown in the figure, some communication also needs Both parties agree on the data transmission rate for better synchronization.
In synchronous communication, most of the content transmitted by the data signal is valid data, while asynchronous communication will contain various identifiers of the frame, so the efficiency of synchronous communication is higher, but the allowable error of the clocks of both parties in synchronous communication is small. , and the allowable error of the clocks of both sides of the asynchronous communication is relatively large.
communication rate
A very important parameter to measure communication performance is the communication rate, which is usually expressed in bit rate (Bitrate), that is, the number of binary digits transmitted per second, in bits per second (bit/s). A concept that is easily confused with bit rate is "Baudrate", which indicates how many symbols are transmitted per second. The symbol is the concept of communication signal modulation. In communication, symbols with the same time interval are often used to represent a binary number. Such a signal is called a symbol. For example, in common communication transmission, 0V is used to represent the number 0, and 5V is used to represent the number 1, then a symbol can represent two states 0 and 1, so a symbol is equal to a binary bit, and the size of the baud rate is related to the bit. The rate is the same; if in communication transmission, 0V, 2V, 4V and 6V represent binary numbers 00, 01, 10, 11 respectively, then each symbol can represent four states, that is, two binary bits, so the symbol The number is half the number of binary bits, and the baud rate at this time is half the bit rate. Because one symbol in many common communications represents two states, people often directly use baud rate to represent the bit rate. Although there is nothing wrong with it strictly speaking, I hope you can understand the difference between them.