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About Serial Servers
Serial servers are used to connect serial devices to a Local Area Network (LAN) / Wide Area Network (WAN) without additional hardware. Serial servers can be used as terminal servers, remote access servers, and modem pooling devices. They are also used to transparently extend server serial ports over LANs in Unix, Linux and Windows environments. For the most part, serial servers are stand-alone devices (not built into an existing system), designed for desktop or rack mounting.
There are a number of recommended standards used by serial servers for serial communication. The most important among these are RS232, RS422 and RS485:
RS232: Is a serial communications standard that provides asynchronous communication capabilities, such as hardware flow control, software flow control, and parity check. It has been widely used for decades. Almost all gears, instruments with digital control interface, and communications devices are equipped with the RS232 interface. The typical transmission speed of an RS232 connection is 9600 bps over a maximum distance of 15 meters.
RS422: Is a serial communications standard that provides a much longer transmission distance, but fewer signal lines compared to RS232. RS422 uses differential transmission technology, and thus provides high-speed transmission of up to 10 Mbps. The maximum transmission distance is 1.2 km at a transmission speed of 9600 bps.
RS485: Is an enhanced version of RS422. It uses a 2-wire bus topology, and is compatible with the RS422 interface. By using an RS485 2-wire bus, you can establish a very economical network. However, RS485 only defines electrical signal specifications; users must define the software protocol themselves.
Most serial servers are designed to handle only one of the recommended standards, although some types do have selectable ports that can handle all three. Some types of serial servers can be configured to manage a much wider range of less common serial protocols including I2C (Inter-Integrated Circuit), SPI (Serial Peripheral Interface), Microwire, and 1-Wire.
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