The serial communication interface (SCI) allows computer components to communicate with each other, either within a computer or with external devices. The RS-232 standard defines the details of the interface, including voltage levels and pin identification. UART was one of the first serial communication interfaces developed. Data is sent in sequences of five or eight bits, with a start and stop bit framing the transfer. SCI technology is used in USB, Serial ATA, PCI-E, Ethernet, and fiber optics.
The serial communication interface (SCI) is a means by which computer components can communicate with each other. This can be within a computer itself, such as from an embedded microchip via the serial bus of a circuit board or expansion card, or via a cable to an external device such as a keyboard or printer. Serial interfaces are also used for some computer networking technologies.
The details of the serial communication interface are discussed in Recommended Standard 232 (RS-232), originally devised in 1962 by a standards group that eventually became known as the Electronic Industries Association (EIA). RS-232 describes, at one end of a serial communication, data terminal equipment (DTE) and data circuit terminating equipment (DCE) at the opposite end. The standard further describes voltage levels and other electrical attributes for the signal, pin identification for the physical interface, circuit functions, and more.
From the RS-232 standard, one of the first serial communication interfaces developed is what is known as a universal asynchronous receiver and transmitter (UART). The first UART provided a means for teletype machines to transfer small five-bit sequences known as Baudot codes. Later, as the use of digital computers increased, the American Standard Code for Information Interchange (ASCII) standard described the encoding of characters in an eight-bit format, which were serially transmitted between computers via integrated circuits and serial interfaces around to 1971. communication interface phrase for their UART a few years later.
The way a serial communication interface works is by sending groups of data, called words, in these sequences of five or eight bits over the cable or computer bus. The bits are sent one at a time in sequence, with a start bit starting the communication, followed by the data bits and a stop bit closing the transfer. Depending on the usage, a check bit, called parity, may also be placed in the sequence to ensure that the data has been transferred intact. This method of framing data transfer within a start and stop bit allows for asynchronous communication. The serial interface is not required to keep time with a synchronized clock, but is instead allowed to send a frame at a given time that the receiving device can recognize.
Serial communication interface technology has found use in numerous areas. A popular method is the universal serial bus (USB) for connecting peripheral devices to a computer. Inside computer cases, hard disk drives sometimes use an interface known as a Serial Enhanced Technology Link (Serial ATA) for high-speed communication with the computer processor. Many expansion cards use another type of serial interface called PCI-E (Peripheral Components Interconnect Express). However, serial communication interfaces are reminiscent of their roots and are also used in common Ethernet networking environments, as well as high-speed fiber optics.
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