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What is a Serial Port?

Serial Port


We can also judge from its name that this pin that this may be the pin used for data communication. So we can say that Serial port is such a device which is used for communication of data in a serial manner. and an important thing to remember here is that this port can communicate only one bit at a time.

serial portserial port

Serial port is now used in almost all type of computers and it is used to connect some some devices like modems, monitors, LCDs and some models of printers to the mother board of computer. If we talk broadly then some devices connected to the computer like Ethernet, USB etc  also requires serial data stream for communication but the name serial port is reserved for that case when you connect a Modem or some similar device which needs to communicate data in a serial manner. Serial ports have been used in past with almost all models of the computers but with the invention of modern technologies like USB, FireWire and some other faster means of data communication, serial ports have been eliminated now and are now replaced by the modern means of data communication. If you still have a old model of a computer at your home or work and you wish to identify that which one is serial port then, look at the back side of your computer and you will observe a 8 pins D shape male connector. As i have shown one of them in the featured image of this tutorial. Now lets move towards the hardware of the serial port and see whats hidden inside this small port and what are the practical applications of this port.

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The old models of IBM computers had been using a small electronic integrated circuit named as UART and it was used to transmit and receive data to and from a external asynchronous device in a serial manner. But with the inventions of modern technology some small home computers then started to make a algorithm in which CPU was used directly to send and receive data from external means. And this technique was known as bit-banging technique.What is a Serial Port?

Early invented computers also have a at-least one serial port and this serial port had different pins in it and every pin was designed to work on a different voltage level, and this serial pin was compatible to work with RS-232. But there was a problem with the operation of such system that the serial port was unable to understand the different voltage levels of RS-232 and different manufacturers had different devices that operated on different voltage levels. So there was need to design such device which should be able to work on same voltages and should be compatible with all the devices, of any manufacturer. Now with the invention of modern devices like USB, FireWire the modern and even low cost processors are able to serial communicate data with a faster speed. And they are able to support devices like mass storage, sound players and video player devices. Now a days in-spite of that fast that what have been invented, every personal computer in use also contains a serial port. The small laptops have a very conserve space so it is possible that some companies may have omitted serial ports from their models but as i have stated above that serial ports had been used for a very long time periods and the circuits used to control and operate the serial ports have become very cheap and some models also comes with the serial port chip fabricated with the circuitry of parallel port.

Pin Configuration of Serial Port:


Serial port have total 9 pins. Every pin has its own functioning and purpose. The purpose of each pin is explained below as:

  • The pin#1 of serial port is named as ‘DCD’. The purpose of pin#1 is Data Carrier Detect. It is used to detect the data stream which is being carried bu the buses for sending to other devices or for receiving.
  • Pin#2 of serial port is named as ‘RxData’. The purpose of this pin is to monitor the data which is received by serial port from some external means.
  • The next pin which is pin#3 of serial port is named as ‘TxData’. The purpose of this pin is to transmit data from serial port to the external module, where we wish to send data. Remember that serial port only transmit data at the rate of one bit per second.
  • Pin#4 of serial port is named as ‘DTR’ and it is called Data Terminal Ready. The purpose of this pin is to see the data which is to transmit but it has not been sent yet. The data is available at the sending port of serial port and it needs the go signal from micro processor.
  • Pin#5 of the serial port is ‘GND’ and it provides ground to the serial port voltages for data communication.
  • Pin#6 is ‘DSR’ and it is abbrivation of Data Set Ready. This pin is used to determine the data transmission rate. Data is available at the port but it has not been sent yet.
  • Pin#7 is ‘RTS’. This pin is the signal for sending the data to external means. When data is available at pin#3 of the serial port and to send this data you have to get permission from control circuit and pin#7 which is in fact RTS pin does this job.
  • Pin#8 is ‘CTS’. It is known as Clear to send. When pin #7 gets requests to send the data and if it gets the permission then data is now ready to send and pin#8 sends it in serial manner.
  • Pin#9 is the last pin of serial port it is a ring indicator and it is abbreviated as ‘RI’.

Applications and Usage of Serial Port:

Serial port possess a large no of practical applications and usage. It is true that it have been eliminated by the modern technology but still there are many devices which are only connected through serial port. Some of serial port’s applications are listed below as:

  • They are most commonly used on some engineering projects with micro controller, where they have to communicate with a personal computer or some other similar devices.
  • Biggest application of serial ports is that they are used to connect to modems.
  • LCD and flat screen monitors are used to connect to the computers through this serial port device.
  • Some devices which are used for network sharing are also connected through this serial port. Some networking devices are like firewalls and rotors etc.
  • Serial port is also used in special applications of GPS (global positioning system) and they are used either to send data or to receive data in serial manner.
  • Also used for scanning bar codes of different products. Mostly serial port is used in some big shops and markets to detect which product you are selling.
  • Serial port sends or receive data in a serial manner, so they are also used in some applications where you wish to display some text on a particular LCD.
  • Serial port is a portable and very much sensitive device and it is also used is modems of satellites and also in some transceivers.
  • Used in some digital testing and measuring electrical instruments like digital multimeter. Where you measure the voltages or current of a particular system.
  • Serial ports have a variety of applications in some mechanical design CNC machines. In these machines, serial port is used to transmit or receive data from micro controller of the machine.
  • Also used in some definite models of UPS (uninterruptible power supply). These UPS are specially designed to operate with computers or LCDs.
  • Used to connect some old models of printers or digital cameras with your computer.
  • The early models of telescopes also had a port for serial port and used for serial data communication.
  • Serial port is also used to operate serial type mouse.


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