Serial port

Serial port (9-pin)

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Serial port is a type of interface found on computers for connecting peripherals. It is also known as a serial communication port. Serial ports allow devices to be connected to a computer and transfer data one bit at a time. This is in contrast to a parallel port which allows for multiple bits to be transferred simultaneously. Serial ports have been used for a wide range of applications, including connecting mice, modems, and printers, although they have been largely replaced by USB and other interfaces in modern computers.

History

The serial port has its origins in telegraphy and was one of the earliest forms of computer communication interfaces. The design and functionality of the serial port were standardized in the early days of computing, which led to its widespread adoption. The most common standard for serial ports is the RS-232C, or more simply, RS-232, which was introduced in 1969.

Design and Operation

A serial port transmits data as a series of sequential bits. This is different from a parallel port which transmits multiple bits simultaneously. The serial port uses a male connector with 9 to 25 pins. Of these, two pins are used for sending and receiving data (transmit and receive), while the others are used for signaling and control purposes.

The data transmission through a serial port is managed by a UART (Universal Asynchronous Receiver/Transmitter), a piece of hardware that converts the bytes of data from the computer into a single serial bit stream for transmission. Upon reaching the destination, another UART reassembles the bits into complete bytes.

Applications

Historically, serial ports were used to connect a variety of devices to computers, including modems, mice, and printers. They were also commonly used for networking purposes and for connecting to console ports on routers and switches in network environments. In industrial settings, serial ports are still used to connect to and control various equipment due to their simplicity and reliability.

Decline and Legacy

With the advent of USB in the mid-1990s, the use of serial ports in consumer electronics began to decline. USB offered faster data transfer speeds, plug and play capabilities, and the ability to supply power to connected devices, features that serial ports lacked. However, serial ports are still found in some applications where a simple, low-speed, and long-established method of communication is sufficient. They are also used in embedded systems due to their simplicity and low cost.

Technical Specifications

The RS-232 standard defines the voltage levels that constitute logical one and zero levels. Logical "1" is defined as a voltage between -3 to -25V, while logical "0" is a voltage between +3 to +25V. This inverse logic is one of the distinctive features of RS-232 serial communication.

See Also

• USB
• Parallel port
• Modem
• UART
• RS-232

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