How to share serial port over Ethernet
This article is dedicated to serial ports: we’ll find out what serial ports are, what they are used for, and how they can be shared over network. We will consider software, as well as hardware solutions for Windows and Linux.
Shall we start?
- What is serial (COM) port?
- Share COM port over Ethernet – Windows
- Share COM port over Ethernet – Linux
- Hardware solutions for serial port sharing
What is serial (COM) port?
There are basically two forms of data communication – serial and parallel, the latter being a relatively recent invention. Although parallel communication works much faster than serial, its use is not always practical, especially for long distances. Serial transmission is typically used between two computers or from a computer to an external device located some distance away. Parallel transmission either takes place within a computer system or to an external device located a close distance away.
A serial port is a serial communication physical interface through which data is transferred. Serial ports have been an indispensable part of computers for more than 20 years, and only recently USB connections have started replacing them. Serial ports are still used in applications such as industrial automation systems, scientific instruments, point of sale systems and some industrial and consumer products.
Serial ports are also known as COM ports, they are bi-directional. This means that devices connected to these ports can receive and transmit data simultaneously. Full-duplex communication, i.e. information can travel in both directions at the same time, is enabled by use of different pins.
To function properly serial ports rely on a special controller chip, the Universal Asynchronous Receiver/ Transmitter (UART). The chip takes the parallel output of the computer's system bus and transforms it into serial form for transmission through COM port. A buffer built in most UART chips enables caching data coming in from the system bus while the chip is processing data going out to the COM port.
Data buffered can be anything from 16 to 64 kilobytes. Majority of standard serial ports transfer data at 115 Kbps (kilobits per second), high speed serial ports, such as Enhanced Serial Port (ESP) and Super Enhanced Serial Port (Super ESP), can reach data transfer rates of 460 Kbps
What are serial ports for?
As we mentioned above, serial ports are used for various equipment and devices to communicate with computers and servers.
Here we are listing some of these devices:
- Mouse. Typically computers with no PS/2 or USB port make use of a serial port to connect to a mouse. Some special mice also connect to a serial port;
- Modem. Mostly older computers, although some find it easier to use modem via serial port even if their computers are equipped with a USB port.
- Network. This is what serial ports were originally used for – to connect computers and allow large files transfer between them.
- Printer. Older printers and plotters
- Telecommunication equipment. For debugging, watching the boot up messages, kernel upgrading using PPC boot, and especially for problems with Ethernet.
- Temperature measuring devices. They connect only via RS-232 ports.
- Diagnostic tools
- Credit card readers, etc.