UK How a serial to Ethernet converter works
A serial to Ethernet converter is a small network device with one or more serial ports on one side and an Ethernet port on the other. In industry it is usually called a serial device server. It takes the bytes arriving on its serial port, packs them into TCP or UDP packets and sends them across the network, and turns packets coming back into serial data for the device.
The point is distance and sharing. An RS-232 cable is good for around 15 m and links one device to one computer. Once the serial port is on the network, a SCADA server, a test PC or a maintenance laptop can reach the device from anywhere the network goes, and one computer can talk to devices spread across a site.
Most converters do not understand the data they carry. They move bytes, and the software at the far end still has to speak the device’s own protocol, whether that is a barcode string, an instrument command set or Modbus RTU.
Operating modes
Converters offer several modes, and the right one depends on how the software at the other end expects to see the device.
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Virtual COM port. A driver on the host computer creates a COM port that is really a network connection to the converter. Existing serial software keeps working unchanged. RFC 2217 is the open standard that lets the host change the remote port’s baud rate and settings.
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TCP server. The converter listens on a TCP port and the host software connects to it directly, with no driver, which suits applications written for network sockets.
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TCP client. The converter connects out to a server when data arrives, useful when many remote devices report to one central application.
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UDP. Data is sent as datagrams to one or several hosts, with lower overhead and no delivery guarantee.
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Paired tunnel. Two converters link two serial devices across an IP network, replacing a long serial cable or a leased line.
Latency, packing and serial settings
Serial devices send data a byte at a time, while networks prefer full packets. Converters therefore buffer incoming bytes and send them when a delimiter character arrives, a buffer fills or a short idle timer expires. Those packing settings matter: too long a timer adds delay, and too short splits messages across packets, which can break protocols such as Modbus RTU that rely on gaps between frames.
The serial side still needs the right baud rate, data bits, parity and stop bits, and on RS-422 or RS-485 the right wiring, termination and biasing. Many industrial converters add isolation on the serial port, a DIN rail mount and a wide DC input for use in cabinets.
Converter or local computer: the alternatives
A converter extends a serial port across the network, but the device’s software still runs somewhere else. The other approach is to put the computer next to the device and send only results across the network. Which one fits depends on where the logic should live.
| Serial to Ethernet converter | COM ports in a local computer | IIoT gateway | |
|---|---|---|---|
| Where the software runs | On a remote PC or server | Next to the device | Next to the device |
| Understands the device protocol | No, it moves bytes | Yes, in the application | Yes, in its protocol software |
| Sensitive to network delay | Yes, every byte crosses the network | No | No, only results cross the network |
| Keeps working if the network drops | No | Yes | Yes, and buffers data |
| Change needed to existing software | Usually none, via a virtual COM port | None | Data reaches it as Modbus TCP, OPC UA or MQTT |
| Best suited to | Extending a few ports to a central host | Machine control and HMI software | Collecting data from many devices for SCADA or the cloud |
Native COM ports are still common on industrial computers: our DIN rail PCs and box PCs typically carry RS-232/422/485 ports, and more ports can be added with serial I/O modules such as Mini PCIe and PC/104 serial cards. Where data from many serial devices has to reach SCADA or a cloud service, our industrial IoT gateways poll the devices locally and publish the results over Ethernet or cellular.
Quick answers on serial to Ethernet
Serial to Ethernet: common questions
Can you convert serial to Ethernet?
Yes, but not with a passive adapter. Serial and Ethernet use different signals and framing, so an active converter, a computer with a serial port or a gateway is needed to carry serial data over a network.
Is RS-232 the same as Ethernet?
No. RS-232 is a point-to-point serial interface running at kilobits per second over a few metres. Ethernet is a packet network running at megabits or gigabits per second over up to 100 m per copper link, with switches joining many devices.
How do I convert RS-232 to RJ45?
It depends what the RJ45 is for. Network equipment console ports carry RS-232 on an RJ45 socket, so a simple DB9-to-RJ45 console cable is enough. To reach a device over an Ethernet network, you need a serial to Ethernet converter.
Can RS-485 be converted to Ethernet?
Yes. Most converters support RS-485 as well as RS-232 and RS-422. For Modbus RTU devices, a protocol-aware gateway that presents them as Modbus TCP is usually easier to integrate than a byte-level converter.
What is the difference between a device server and a terminal server?
Mainly the use. A device server connects machines and instruments to applications. A terminal or console server gives administrators remote access to the console ports of servers, switches and routers, often as part of out-of-band management.
We fit serial ports and cards in industrial computers and gateways as standard, set each port’s mode and termination, and install the drivers and software before the system ships. Tell us which serial devices you need to connect and where their data has to go, and we will specify the hardware to match.