Với sự phát triển của tự động hóa công nghiệp, việc ứng dụng máy tính bảng trong công nghiệp ngày càng trở nên phổ biến. Trong khi chúng tôi hiểu nhu cầu của khách hàng, khách hàng cũng sẽ hỏi một số câu hỏi chuyên môn về cấu hình, chẳng hạn như các vấn đề về giao diện của máy tính bảng công nghiệp, công nghiệp Sự khác biệt giữa RS-232, RS-422 và RS-485 trên bo mạch chủ là gì? Công dụng của chúng là gì
What is the difference between RS-232, RS-422 and RS-485 on industrial motherboards?
1. RS-232
RS-232 has many uses in industrial motherboards, such as connecting a mouse, printer or modem, and also connecting industrial instruments. RS-232 is limited to point-to-point communication between industrial motherboard serial ports and equipment, and the long-distance communication distance is 15.24 meters.
2. RS-422
RS-422 uses differential signals, and RS-232 uses unbalanced ground reference signals. Differential transmission uses two wires to send and receive signals, which can better resist noise and have a longer transmission distance. It has great advantages in field applications of industrial motherboards.
3. RS-485
RS-485 is an improvement of RS-422. The number of link devices has been increased from 10 to 32. At the same time, the electrical characteristics of the large number of devices are defined to ensure sufficient signal voltage. Strong anti-noise and multi-device capabilities. When establishing a distributed device network connected to an industrial computer, other data collection controllers, HMI or other operations, the serial connection will choose RS-485.
4. Stop bit: used to indicate the last bit of a single packet. Typical values are 1, 1.5 and 2 bits. Since the data is timed on the transmission line, and each device has its own clock, it is likely that the two devices are slightly out of sync during the communication. Therefore, the stop bit not only indicates the end of the transmission, but also provides an opportunity for the industrial computer to correct the clock synchronization. The more the number of bits applicable to the stop bit, the greater the tolerance for synchronization of different clocks, but the slower the data transmission rate is at the same time.
5. Data bit: It is a parameter to measure the actual data bit in communication. When an industrial computer sends an information packet, the actual digits will not be 8 digits. The standard values are 5, 7 and 8 digits. How to set depends on the information you want to transmit. For example, the standard ASCⅡ code is 0127 bits (7 bits). The extended ASCⅡ code is 0-255 (8 bits). If the data uses simple text, then each data packet uses 7 bits of data. Each packet refers to a byte, including start/stop bits, data bits and parity bits.
6. Baud rate: It is a parameter of communication speed, which represents the number of bits transmitted per second. For example, 300 baud means sending 300 bits per second. When referring to the clock cycle, it refers to the baud rate. If the protocol requires 4800 baud rate, then the clock is 4800Hz. But the baud rate is inversely proportional to the distance. High baud rates are often used for communication between short-distance instruments. A typical application is communication with GPIB devices.
7. Parity bit: a simple error detection method in the serial communication of industrial motherboards. There are four error detection methods: even, odd, high and low. Of course, it is also possible to have no check digit. In the case of even and odd parity, the serial port will set the parity bit, and use a value to ensure that the transmitted data has even or odd logic high bits. If the data is 011, then for even parity, the parity bit is 0 to ensure that the number of logic high bits is an even number. If it is odd parity, the parity bit is 1, so there are 3 logic high bits. The high and low bits do not really check the data, simply set logic high or logic low to check. In this way, the receiving device can know the status of a bit and have the opportunity to judge whether there is noise interfering with the communication or whether the transmission and reception data are out of sync.
8. Serial port
Serial port is a very common device communication protocol on industrial motherboards. Most industrial motherboards contain more than two RS-232-based serial ports. The serial port sends and receives bytes by bit, and the speed is slower than the parallel communication by bytes, but the serial port can use one wire to send data while using another wire to receive data, which can easily realize long-distance communication.
9. The difference between RS-232, RS-422 and RS-485
RS-232, RS-422 and RS-485 are all serial data interface standards, which were originally formulated and issued by the Electronics Industry Association. RS-232 was released in 1962 and named EIA-232-E as an industrial standard to ensure compatibility between products from different manufacturers. RS-422 is developed from RS-232. In order to improve the shortcomings of RS-232 communication distance and low speed, RS-422 defines a balanced communication interface, which increases the transmission rate to 10Mb/s and the transmission distance to 4000 feet, and allows multiple connections on a balanced bus. 10 receivers. RS-422 is a unidirectional, balanced transmission specification for single machine sending and multiple machine receiving, and it is named TIA/EIA-422-A standard. In order to expand the scope of application, EIA formulated the RS-485 standard on the basis of RS-422 in 1983, adding multipoint and two-way communication capabilities, that is, allowing multiple transmitters to be connected to the same bus, and at the same time adding transmitters The drive capability and conflict protection features of the NAS extend the common mode range of the bus, that is, the TIA/EIA-422-A standard.
