The serial line sounds like a term from the past, but in networks, industry and service it is alive today. Through it, switches, routers and industrial devices are configured. Let us explain in detail what serial communication is, how it works and why it is still used.

What serial communication is

Serial communication is a way of transferring data in which individual bits go one after another, one by one, over a single wire. The opposite is parallel transfer, where several bits go at once over several wires. Serial transfer is simpler, more reliable over longer distances and gets by with few wires.

RS-232 is the best-known serial communication standard, which defines the voltages, wiring and the way of transfer. You meet it under the names serial port, COM port or console port.

How the serial line works

Imagine it as a narrow tunnel through which only one bit passes at a time. For both sides to understand each other, they must agree on the rules:

  • Speed (baud rate). How many symbols per second are transferred, for example 9600 or 115200. Both sides must have the same speed, otherwise they do not understand each other.
  • Data bits. How many bits form one character, most often 8.
  • Parity. A simple error check, often disabled (none).
  • Stop bits. Marking the end of a character, usually 1.

A common setting is written for example as 9600 8N1 (9600 baud, 8 data bits, no parity, 1 stop bit). When these values match on both sides, communication works.

What the serial line is still used for

Although the serial port has almost vanished from ordinary computers, in these areas it is irreplaceable:

  • Configuring network equipment. Switches and routers (especially managed ones) have a console port through which they are configured, when they do not yet have a network or when remote access fails. For a network administrator it is a basic tool.
  • Industrial and control systems. Machines, automatons, measuring and control devices often communicate over a serial line.
  • Embedded systems and electronics. When developing and debugging devices (including Arduino and ESP32), the serial line is a standard way of communication.
  • Service and diagnostics. When repairing or initially setting up a device that is otherwise inaccessible.
  • Older devices (cash registers, scales, some instruments) that have no other port.

How to connect today

Modern laptops no longer have a serial port, so a USB-to-serial adapter is used. After connecting, a virtual COM port appears on the computer. For the communication itself, a terminal program (for example PuTTY) is used, where you enter the correct COM port and settings (speed, bits, parity). This relates to working in the command line and terminal.

With network devices, a specific console cable is often needed (often with an RJ45 connector on the device side).

What to watch for

  • The same setting on both sides, otherwise you see only gibberish. The most common mistake is the wrong speed (baud rate).
  • The correct COM port on the computer (check in Device Manager).
  • A quality adapter and drivers, cheap USB adapters sometimes cause problems.

Conclusion

The serial line and the RS-232 standard transfer data bit by bit, and although they have vanished from ordinary computers, in networks, industry and service they are still key. Through the console port, switches and routers are configured, industrial devices and embedded electronics communicate. You just need to know the correct setting (for example 9600 8N1) and have a USB adapter.

Need to configure a switch, router or industrial device via the serial line? Get in touch, we have the tools and experience for it.