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In telecommunication and data transmission, serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. This is in contrast to parallel communication , where several bits are sent as a whole, on a link with several parallel channels.
Synchronous serial communication describes a serial communication protocol in which "data is sent in a continuous stream at constant rate." [1]Synchronous communication requires that the clocks in the transmitting and receiving devices are synchronized – running at the same rate – so the receiver can sample the signal at the same time intervals used by the transmitter.
The total speed includes bits for framing (stop bits, parity, etc.) and so the effective data rate is lower than the bit transmission rate. For example, with 8-N-1 character framing, only 80% of the bits are available for data; for every eight bits of data, two more framing bits are sent.
Data communication, including data transmission and data reception, is the transfer of data, transmitted and received over a point-to-point or point-to-multipoint communication channel. Examples of such channels are copper wires , optical fibers , wireless communication using radio spectrum , storage media and computer buses .
The last data bit is sometimes used as a parity bit. The number of data and formatting bits, the order of data bits, the presence or absence of a parity bit, the form of parity (even or odd) and the transmission speed must be pre-agreed by the communicating parties. The "stop bit" is actually a "stop period"; the stop period of the transmitter ...
(the START bit), waits 'half a bit duration' and then reads the value of the signal. A further delay of one 'whole bit duration' is executed before the next data bit is 'read' - repeating for the length of the whole serial word (typically 7/8-data bits). An optional PARITY bit follows the data bits and precedes the stop bit(s).
A data packet consists of the PID followed by 0–1,024 bytes of data payload (up to 1,024 bytes for high-speed devices, up to 64 bytes for full-speed devices, and at most eight bytes for low-speed devices), [12] and a 16-bit CRC. There are two basic forms of data packet, DATA0 and DATA1. A data packet must always be preceded by an address ...
An example of an early 1980s UART was the National Semiconductor 8250 used in the original IBM PC's Asynchronous Communications Adapter card. [5] In the 1990s, newer UARTs were developed with on-chip buffers. This allowed higher transmission speed without data loss and without requiring such frequent attention from the computer.