Serial Server Protocols: Understanding RS-232, RS-422, and RS-485

Time : Feb. 14, 2023    View : 128

Serial servers are widely used to connect serial devices, such as modems, printers, and industrial equipment, to Ethernet networks. However, not all serial devices use the same communication protocol. In this article, we’ll explore the differences between three popular serial protocols: RS-232, RS-422, and RS-485.

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RS-232 RS-232 is a serial protocol that has been widely used since the 1960s. It is a point-to-point protocol, meaning that it allows communication between two devices over a single line. RS-232 uses a voltage range of -15 to +15 volts to represent binary data, with negative voltages indicating logic 1 and positive voltages indicating logic 0. The protocol supports a maximum cable length of 50 feet, making it suitable for short-range communication.


RS-422 RS-422 is a differential serial protocol that was developed in the 1970s. It is designed for longer-range communication, with a maximum cable length of 4,000 feet. RS-422 uses differential signaling, meaning that it sends two complementary signals over two separate wires. The difference between the two signals represents the binary data. This method provides better noise immunity and enables faster communication than RS-232. Additionally, RS-422 supports multi-drop communication, which means that up to 10 devices can be connected to a single line.


RS-485 RS-485 is a differential serial protocol that is similar to RS-422 but with additional features. Like RS-422, it uses differential signaling and supports multi-drop communication. However, RS-485 can support up to 32 devices on a single line, and it provides greater noise immunity than RS-422. Additionally, RS-485 supports half-duplex communication, meaning that data can be sent in both directions, but not at the same time.


In summary, RS-232 is a point-to-point protocol suitable for short-range communication, while RS-422 and RS-485 are differential protocols that support longer-range and multi-drop communication. RS-422 is faster and has better noise immunity than RS-232, while RS-485 provides even greater noise immunity and supports more devices on a single line.


When choosing a serial server for your business, it is important to understand the communication protocol used by your serial devices. Some serial servers support multiple protocols, while others are designed specifically for one protocol. By choosing the right serial server, you can ensure reliable and efficient communication between your serial devices and your network.