- Published 12 Jun 2023
- Last Modified 29 Aug 2023
- 7 min
What are Serial Ports for?
Serial ports can be found on computers, devices and in various parts of computer networks, but what are they and how do they work?
Reviewed by Mithun Subbaroybhat, Technical Support Engineer (December 2022)
Serial ports date back much farther than you’d imagine, and their uses are wide-ranging. From your USB to virtual ports, these connectors cover a lot of ground. And, in the case of USB, it’s become something we use every day. Modern life wouldn’t be the same without it.
What are Serial Ports?
Serial ports are computer components which were invented in the 1960s, to connect and transfer data from electric typewriters to modems. These specific ports were referred to as RS-232 ports. As technology progressed, they were used in computers and served as an easy way to connect devices.
A serial port is usually male, meaning that the port has pins sticking out, which slot into the female cable. The modern port has a nine-pin connector, but the older serial ports used to have 25 pins. However, these ports made data transfer slower, which meant the 9-pin port became the standard. The naming conventions typically match up to the pin numbers. Often ports will be referred to as 32-pin connectors for example.
When attempting to find a serial port on software or systems, these ports are discoverable as COM followed by a number, such as COM 1, COM 2, and COM 3. The USB port is also considered a serial port, with USB standing for Universal Serial Bus. Unlike the traditional RS-232 serial port, these have been developed to transfer data at a much faster rate and are included as standard in most electronic technology.
Finally, Virtual Serial Ports are software that mimics the function of a serial port, without the use of a physical object. Due to the port being virtual, the user has more functionality with this kind of port.
What are the Main Use Cases for Serial Ports?
Today the traditional serial port is less common but is still in use. They can be found on flat-screen monitors, barcode scanners and GPS receivers. They often act as a physical connection between a system and electronic machinery, transferring information between the two to complete a task.
This kind of port is more commonly found on industrial machinery, rather than household items. However, older computers also came equipped with serial ports, and serial cards can be used to add serial port connectivity to a server or computer. PC serial ports and allowed for the connection of modems, security cameras and computer mice. Traditional serial ports are also a great tool for communication. They can be used in processors to connect different parts of a system and transfer data securely.
The more modern USB (universal serial bus) port is used for a variety of tasks. These include data transfer, charging electronics and transferring images and audio. These ports can transfer at a much faster rate and are the standard in household electrical objects. In fact, the USB connector, in its full-sized, micro, and mini forms, is probably the most ubiquitous connector in the world.
Virtual serial ports are used for port sharing. This means that two sets of data can be sent at once, rather than one series of data, for more speedy transfers. Virtual serial ports are also used in Bluetooth and network transmissions.
What Do Serial Ports Do?
The purpose of a serial port is to transfer data one bit at a time. Whilst a slower data transmission, this type of port was a more secure way to transfer data. Their slow transmission means that only a single piece of wire is needed to transmit data from one device to another. Like USB ports, serial ports can also receive data as well as send it.
Serial ports rely on a UART chip to function. UART stands for Universal Asynchronous Receiver/Transmitter, and its purpose is to serialise the data received or to be transmitted. Standard serial ports transfer data at an approximate speed of 114kbps, whereas enhanced serial ports have a higher transfer speed of 460kbps.
Serial ports also utilise flow control. Flow control allows serial transfer to be paused and resumed if the device receiving information cannot process it at the speed the serial connection is sending it. This inbuilt system of serial connection stops devices from overloading and makes data transfer more secure.
What is the Difference Between Serial and Parallel Ports?
Whilst both serial and parallel ports are responsible for sending and receiving data, it’s how they transfer data that differs. Serial ports send a series of single lines of data. Their data transfer is slow, and they use only a single wire to transfer data. Serial ports usually have a D-shaped, 9-pin connector.
Parallel ports send large amounts of data at one time in a parallel way. They have a D-shaped 25-pin connector. These cables contain multiple wires for data transfer and all the wires need to transfer at the same speed to prevent errors. Due to this, the wires that connect to parallel ports are much smaller. Parallel ports are more commonly used for hard drives, printers, and CD drives. Unlike serial ports, parallel ports are usually female with a male connector.
How to Test Serial Ports
The easiest way to test serial ports is with serial port testing software. This software is downloaded and will run tests on the input and outputs of your port. These tests will produce a report consisting of code. This code acts as a report of the data transmitted through your serial port.
Once the port testing software has run multiple tests, it will compare its code reports to check consistency in the coding. This consistency check will include the information provided and the speed at which that information was transmitted.
You can also check a serial port is working by checking the driver is installed in the control panel settings of your computer. Testing with multiple connectors is also a great way to ensure your serial port is operating consistently.
Serial Communication
Serial communication refers to the process of transferring data one bit at a time, sequentially over a single communication channel. It is commonly used in various devices and systems to transmit information between two or more entities. Serial communication can be further classified into synchronous and asynchronous communication, depending on how the data is synchronized between the sender and receiver.
Synchronous Communication
In synchronous communication, data transmission is synchronised using a clock signal shared by both the sender and receiver. The clock signal ensures that the sender and receiver operate at the same time, allowing them to correctly interpret the transmitted data. The data is divided into frames, and each frame consists of a fixed number of bits. Both sender and receiver must use the same frame structure. This includes the number of bits per frame, the order of bits, and the synchronisation scheme.
Synchronous communication offers advantages such as higher data transfer rates, efficient bandwidth utilisation, and reliable data transmission. However, it requires precise synchronisation between sender and receiver, and timing errors can corrupt data.
Asynchronous Communication
In asynchronous communication, data transmission does not rely on a shared clock signal. Instead, each data frame is accompanied by start and stop bits, which frame the data bits and provide synchronisation. The sender and receiver do not need to be synchronised beforehand. The start bit indicates the beginning of a frame, while the stop bit indicates the end. The number of data bits per frame, as well as the parity bit for error checking, can be configured.
Asynchronous communication is commonly used for slower data transfer rates and short-distance communication. It is more tolerant of timing variations and does not require strict synchronisation. However, due to the additional start and stop bits, it has lower bandwidth utilisation than synchronous communication.
