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What is a COM port? - All you need to know about serial port

Olga Weis Olga Weis
  1. What is COM port?
  2. What is Serial Device
  3. What are serial ports used for?
  4. Frequently Asked Questions about COM port

What is a COM port?

A COM port is simply an I/O interface that enables the connection of a serial device to a computer. You may also hear COM ports referred to as serial ports. Most modern computers are not equipped with COM ports (almost all laptops with serial ports are not in use anymore), but there are many serial port devices still in use that use the interface. Lab instruments, medical equipment, and point-of-sale systems often make use of serial connections.

COM port

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So what are COM ports? They are asynchronous interfaces that can transmit one bit of data at a time when connected to a serial device. The COM designation is due to their use as communication ports on IBM compatible computers. In traditional personal computers, COM1 and COM2 were often used to connect a serial port device such as a modem or mouse. Here is what a DB9 COM port looks like.

What is a serial device?

Serial devices are pieces of electronic equipment that are characterized by the way they transmit data. Information is sent and received one bit at a time, which provides for a simple and reliable method of communication.

What is a serial port on a computer?

Serial ports are not standard equipment on the majority of newly manufactured desktop and laptop computers. Maybe you will need a serial adaptor for the laptop. The RS232 serial ports seen in the past are usually replaced with one or more USB interfaces.

This does not mean that you cannot connect a serial port device to a new computer. You can use a USB to serial adapter which can provide single or multiple COM ports to machines that do not have any installed serial interfaces. There are many solutions available, and most are inexpensive and easy to implement.

The adapters work by installing a device driver on a Windows computer. The driver is a program that enables the computer to use the USB to RS232 adapter as a replacement for a serial interface. This is done by creating a virtual COM port that performs identically to a physical port contained on a machine’s motherboard.

What are serial ports used for?

USB interfaces have largely replaced COM ports as a faster way of performing serial data transmission. Most computers are equipped with internal modems, eliminating the need for external serial devices. Similarly, COM-connected mice are no longer widely used to input data. Null-modem cables can be used with serial interfaces to connect two computers, but this method is rarely used anymore.

Serial ports are still used in many specialized situations. Some examples are surveillance cameras and equipment used for industrial automation implementations. They employ the RS232 interface which is still supported by the hardware on many modern computers. Since many cost-efficient serial over Ethernet software and hardware solutions enable COM ports to be used on machines that are not equipped with any, we can expect the RS232 protocol to be around for a while. A COM port also has the advantage of being able to power 15 meters of shielded cable. A comparable USB cable would be limited to a length of 5 meters.

Types of serial ports

Serial ports come in two standard configurations. They are usually male connectors with either 9 or 25 pins. Parallel ports that are used to connect a partner cable are 25 pin female connectors. The accepted manner of naming ports on personal computers labels the serial interfaces as COM1 and COM2 with LPT1 designating a parallel port. Each pin is used for a particular function such as sending and receiving data or sending a terminal ready message. Essentially, any interface that is compliant with the RS232 protocol is a serial port.


Devices That Use Serial Ports

The RS232 protocol is used by many device manufacturers. You will find serial connectivity built into devices like GPS receivers, industrial automation sensors, barcode scanners, and measuring equipment, to name just a few.


UART stands for Universal Asynchronous Receiver/Transmitter. It is a hardware device that translates data between a computer’s parallel and serial ports. UART processing transmits a byte of data serially bit by bit. The data is then converted back to a full byte at the other end of the connection. Using this technology makes it irrelevant whether a parallel or serial port is used for data transmission.

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Frequently Asked Questions about
COM port

A virtual serial port is a software construct that emulates the functionality of a serial interface to enable communication with serial devices using a network or other type of physical port. Virtual serial ports are essential when using serial applications with computers that are not equipped with physical serial interfaces. Virtual serial ports
The protection level of your network connections will depend on the solution you choose. Serial to Ethernet Connector by Electronic Team is one of the most reliable programs when it comes to the security of data transfer. This application deploys advanced traffic encryption that protects your data from unauthorized access or interception. That means all the connections you establish with this software are totally secure.
With Serial to Ethernet Connector, you can share an unlimited number of real and virtual COM ports at a time.
In network terminology, serial tunneling means creating a connection between COM ports of two serial device servers over Ethernet. The communicated serial data is packetized in both directions into TCP/IP packets and redirected across Ethernet.
In RS-232 port connections, the data transfer rate is measured by bits per second (bps). The standard data exchange rates for asynchronous serial communication include:

110, 300, 600, 1200, 2400, 4800, 9600, 14400, 19200, 38400, 56000, 57600, 115200, 128000 and 256000 bps. Note that these values refer to the effective transmission rate, i.e., the rate is determined without taking into account the service bits - start, stop, and parity.

For a long time, the serial port speed above 115,200 bps hasn’t been supported by any operating systems or hardware. But the advanced manufacturing technology of modern motherboards chipsets makes it possible to increase the data exchange rate to more than 1 Mbit/s.

Note that the data transfer rate depends largely on the length of the connecting cable and how it is run relative to the power supply wires.
According to the RS-232 standard, the maximum cable length is 50 feet (or 15.24 m).
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