RS-232 and RS-422 are serial data interface standards, originally developed and published by the Electronic Industries Association (EIA), RS-232 was published in 1962, named EIA-232-E, as an industry standard to ensure compatibility between products from different manufacturers. RS-422 is developed from RS-232, and it is proposed to make up for the shortcomings of RS-232. To improve on the short distance and low rate of RS-232 communication, RS-422 defines a balanced communication interface that increases the transmission rate to 10Mb\/s, extends the transmission distance to 4000 feet (at rates below 100 KB \/s), and allows up to 10 receivers to be connected on a balanced bus. RS-422 is a single-machine transmit, multi-machine receive one-way, balanced transmission specification, named TIA\/EIA-422-A standard. In order to expand the scope of application, EIA also formulated the RS-485 standard in 1983 on the basis of RS-422, adding multi-point, two-way communication capability, that is, allowing multiple transmitters to connect to the same bus, while increasing the drive capability and conflict protection characteristics of the transmitter, extending the bus common model circumference. Later named TIA\/EIA-485-A standard.
Serial Interface is an exponential sequential transmission, which is characterized by simple communication lines, as long as a pair of transmission lines can achieve two-way communication (you can directly use the telephone line as a transmission line), thus greatly reducing the cost, especially suitable for long-distance communication, but the transmission speed is slow. The communication mode in which the data of a message is transmitted bit by bit in order is called serial communication. The characteristics of serial communication are: the transmission of data bits is carried out in bit order, at least only one transmission line can be completed; Low cost but slow transfer speed. The distance of serial communication can be from a few meters to several thousand meters; According to the direction of information transmission, serial communication can be further divided into simplex, half-duplex and full-duplex three kinds.
< br >
RS-232 and RS-422 are two common serial data interface standards, and their main differences are as follows:
< br >
Interface signal level value: RS-232 signal level value is high, easy to damage the interface circuit chip, need to use the level conversion circuit to connect with the TTL circuit; The signal level of RS-422 is low, which is not easy to damage the interface circuit chip.
< br >
Transmission rate: RS-232 in asynchronous transmission, the baud rate is 20Kbps; The RS-422 defines a balanced communication interface that increases transmission rates to 10Mbps, extends transmission distances to 4,000 feet (at rates below 100 KBPS), and allows up to 10 receivers to be connected on a balanced bus.
< br >
Interface form: RS-232 interface uses a signal line and a signal return line to form a common ground transmission form, which is easy to produce common mode interference and weak anti-noise interference; The RS-422 interface uses differential signals, using two wires to send and receive signals, which has better noise resistance and longer transmission distance.
< br >
Transmission distance: RS-232 maximum transmission distance standard value of 50 meters, in fact, can only be used in about 15 meters; The RS-422 can achieve a longer transmission distance.
< br >
In short, RS-232 and RS-422 are different in interface signal level value, transmission rate, interface form, transmission distance, etc., and the choice of the appropriate serial port standard should be determined according to the specific application scenario and needs.
Both the 232 and 422 serial ports are common serial interfaces, but there are some differences between them.
Electrical characteristics: 232 serial port is one-way transmission, using a pair of sending and receiving lines, the communication distance is short (generally not more than 50 meters), the signal level is ±5V; The 422 serial port is a full-duplex transmission, using four lines, a long communication distance (up to 1200 meters), the signal level is ±5V or ±12V.
Signal transmission mode: 232 serial port uses asynchronous transmission mode, that is, bit-by-bit transmission, with stop bit and start bit between each byte, while 422 serial port uses synchronous transmission mode, that is, data bit and clock bit are transmitted at the same time.
Application scenario: 232 The serial port is used to connect a PC to an external device, such as a printer or modem. The 422 serial port is often used in industrial automation, robot control and other fields, which needs to transmit data with a long distance and a high rate.
In short, 232 and 422 serial ports have their own characteristics and application scenarios. Select a proper serial port based on the application scenario.