Equipment with a serial port is usually connected directly to the computer when the distance is less than 15 meters.
With a serial port server (Serial Device Server), the equipment can be connected anywhere on a network so that all network users can use them. This applies to both local and internet. When connected over the Internet, the reach becomes global.
Serial Device Servers
It has the task of making a serial port available on a network. It is a compact computer that has an Ethernet network interface and one or more serial ports. Its firmware is only for sending data from the network to the proper serial port and transmitting data received on serial ports to the network. The protocol is TCP / IP (Internet Protocol), so even a serial port server with many ports has only one IP address and each serial port has its own port number.
Three communication methods
In principle, it can be communicated with serial port servers in 3 different ways:
- The "Winsock" method
- "Virtual com driver" method
- "Box to box" method
Used if there is no computer with network function available. The two serial port servers are configured to send data to the counterpart. They are defined as "Master" and "Slave", each with its own IP address and the counterparty's IP address. In principle, it is a fixed connection between the serial ports and it is important that the connection be independent of operating systems and software versions otherwise used on the network.
The "Box to box" method is also the only usable solution in cases where the system cannot include software that uses "sockets" or COM port drivers, for example. a PLC and a simple measuring port with serial port.
In all common programming languages for Windows (Visual C ++, Visual basic, Delphi and others), TCP / IP is accessed via "Winsock", releasing the programmer to kno
The "Winsock" method
This method assumes that the applications using the serial port server have access to the network via the TCP / IP protocol using the networking features built into Windows. It is the standardized interface for these features called "Winsock".
In all common programming languages for Windows (Visual C ++, Visual basic, Delphi and others), TCP / IP is accessed via "Winsock", releasing the programmer to know all the details of the underlying network protocols.
Once the protocol, IP address, port number and client / server status are selected, free-form data blocks can be exchanged between the program and the serial port server.
Many types and variants
There are a variety of variants among serial port servers. The number of serial ports per. unit varies from 1 to 16, and the serial ports can be traditional RS232 ports with "point to point" connection up to approx. 15 m or RS422 ports with balanced "point to point" signals up to approx. 1200 m and RS485 ports, for "multidrop" connection, where up to 32 serial ports can share the same 2- or 4-wire bus. Here, the range will also be up to 1200 m.
Most serial port servers use the wired Ethernet network interface, others use wireless networks (Wifi) or fiber optic cable, where the network connection is via fiber optic cable.
