What is the difference between RS-232 and RS485?

1, Electrical characteristics
RS-232: RS-232-C is a serial physical interface standard developed by the Electronic Industries Association (EIA) in the United States, which uses a pair of transmission lines (TX, RX) for bidirectional communication. In terms of electrical characteristics, RS-232 adopts a single ended signal transmission method, where a negative signal level represents logic 1 and a positive signal level represents logic 0. Specifically, logic "1" ranges from -3V to -15V, and logic "0" ranges from+3V to+15V. Due to this single ended signal transmission method, RS-232 is susceptible to common ground noise and common mode interference, which limits its application in long-distance communication.
RS485: In contrast, RS485 adopts differential communication protocol and uses two pairs of transmission lines (A, B) for bidirectional communication. The differential signal transmission method enables RS485 to better resist line interference and noise, improving the reliability and stability of communication. In terms of electrical characteristics, the logic "1" of RS485 shows that the A line is at a positive voltage relative to the B line, while the logic "0" is the opposite. The typical differential voltage range is ± 200mV to ± 2V.
2, Data transmission distance and speed
RS-232: RS-232 is usually suitable for shorter distance communication, and its maximum transmission distance is affected by various factors, including environment, cable type, cable length, etc. Under ideal conditions, the maximum transmission distance of RS-232 can reach about 50 meters, but in practical applications, it is often limited by environmental noise and cable attenuation, and is usually used for communication within 20 meters. The maximum data transmission rate of RS-232 is usually 115.2 kbps, which is suitable for low-speed data transmission scenarios.
RS485: RS485 is suitable for long-distance communication, and its transmission distance can reach several kilometers, depending on the communication rate, cable type, and environmental conditions. Under ideal conditions, the theoretical maximum transmission distance of RS485 is approximately 1219 meters, but in practical applications, it is usually less than this value. The transmission rate of RS485 can reach 10 Mbps or even higher, depending on the specific standards and equipment, and is suitable for scenarios that require high-speed and long-distance communication.
3, Network topology structure
RS-232: RS-232 is commonly used for point-to-point connections, that is, one-to-one communication connections. This connection method is simple and direct, but not suitable for communication between multiple devices.
RS485: RS485 supports multi-point communication and can connect multiple nodes using a bus topology structure. This network topology enables RS485 to facilitate communication between multiple devices, making it suitable for scenarios such as industrial automation, building automation, and security monitoring that require multi node communication.
4, Transmission method
RS-232: RS-232 uses full duplex communication to simultaneously send and receive data. This transmission method improves the efficiency of data transmission, but is limited by its electrical characteristics and transmission distance.
RS485: RS485 can use either half duplex or full duplex communication methods. In half duplex mode, only one device can send data at a time, while full duplex mode allows for simultaneous sending and receiving of data. This flexibility enables RS485 to adapt to different communication needs.
5, Application scenarios
RS-232: Due to its electrical characteristics and transmission distance limitations, it is commonly used to connect personal computers and external devices such as printers, modems, etc. The communication distance between these devices is relatively short, and the requirements for data transmission rate are not high.
RS485: RS485 is widely used in industrial automation, building automation, intelligent transportation and other fields due to its long-distance, high-speed and multi node communication capabilities. In these fields, it is necessary to achieve long-distance, high-speed communication between multiple devices, and RS485 is the ideal choice to meet these requirements.