Serial port is a electronic communication gateway used for transferring data one bit at a time.
Together with parallel port the serial port was used almost for all type of information transfer between a computer and other peripheral devices. Today the serial port has been replaced with dedicated ports like usb port (used for data transfer and communication between a computer and other devices), vga port (video data communication), Ethernet port or internet port (used for network communication; any type of information) .
The serial port it is also known as COM port and when a device is connected to it you will found it in device manager on port COM1 or COM2 or …. COMX.
The serial port uses the RS232 standard and the DB9 connector for data transfer and connection. RS232 includes a couple of standards used for serial connections and control signals between data terminal equipment (DTE) and data circuit-terminating equipment (DCE).
Serial port pinout or DB9 connector pinout has the following configuration:
PIN 1 – Data carrier detect (DCD) – IN
PIN2 – Receive data (RXD) – IN
PIN3- Transmit data (TXD) – OUT
PIN4 – Data terminal ready (DTR) – OUT
PIN5 – Signal ground (GND)
PIN6 – Data set ready (DSR) – IN
PIN7 – Request to send (RTS) – OUT
PIN8 – Clear to send – IN
PIN9 – Ring Indicator – RI
The connection between a computer and a peripheral device that uses the rs232 standard is done through a serial cable. The length of the serial cable has a direct influence on the baud rate (transfer rate) so below 50ft you can have a baud rate of 19200 bps, but if you increase the serial cable length the baud rate will decrease as follow: 500ft -9600 bps ; 1000ft-4800 bps and 3000ft-2400bps.
In our days the serial port is most used on industrial devices and programming. Serial port programming is done by using a serial port adapter to a usb port mostly because the new computers are not equipped with db9 connectors. The disappearance of the external serial communication doesn’t mean that this type of data transfer is not used any more on the new PC’s because it migrated inside the computer and you could know it by the name of SATA or serial ata. SATA is used for data transfer between optical devices ( dvd drive ) , hard disk drives and the motherboard.