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

Note: 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.

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.

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.

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.

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.

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.