- Serial communication
telecommunicationand computer science, serial communication is the process of sending data one bitat one time, sequentially, over a communication channelor computer bus. This is in contrast to parallel communication, where several bits are sent together "(on a link comprising of several wired channels in parallel)".
Serial communication is used for all long-haul communication and most
computer networks, where the cost of cableand synchronizationdifficulties make parallel communication impractical. At shorter distances, serial computer buses are becoming more common because of a tipping point where the disadvantages of parallel busses (clock skew, interconnect density) outweigh their advantage of simplicity (no need for serializer and deserializer (SERDES)). Improved technology to ensure signal integrityand to transmit and receive at a sufficiently high speed per lane have made serial links competitive. The migration from PCI to PCI-Expressis an example.
teletypesystems evolved as an automated telegraphysystem called telex. Originally, a rotating mechanical commutator (a rotating switch) was started by a "start bit". The commutator would distribute the other bits to set relays that would pull on solenoids which would cause the mechanism to print a figure on paper. The routing was automated with rotary electromechanical dialing systems like those used in early telephone systems. When computers became commonplace, these serial communication systems were adapted using I/O devices called serial ports that used UARTs. The development of communication hardware had a deep continuing impact on the nature of software and operating systems, both of which usually arrange data as sequences of characters.
Integrated circuits are more expensive when they have more pins. To reduce the pins, many ICs use a serial bus to transfer data when speed is not important. Some examples of such low-cost serial buses include SPI, I²C, and 1-Wire.
erial versus parallel
The communication links across which computers—or parts of computers—talk to one another may be either serial or parallel. A parallel link transmits several streams of data (perhaps representing particular bits of a stream of bytes) along multiple channels (wires, printed circuit tracks, optical fibres, etc.); a serial link transmits a single stream of data.
At first sight it would seem that a serial link must be inferior to a parallel one, because it can transmit less data on each clock tick. However, it is often the case that serial links can be clocked considerably faster than parallel links, and achieve a higher data rate. A number of factors allow serial to be clocked at a greater rate:
Clock skewbetween different channels is not an issue (for unclocked asynchronous serial communicationlinks)
*A serial connection requires fewer interconnecting cables (e.g. wires/fibres) and hence occupies less space. The extra space allows for better isolation of the channel from its surroundings
Crosstalkis less of an issue, because there are fewer conductors in proximity.
In many cases, serial is a better option because it is cheaper to implement. Many ICs have serial interfaces, as opposed to parallel ones, so that they have fewer pins and are therefore cheaper.
Examples of serial communication architectures
Morse code telegraphy
RS-232(low-speed, implemented by Serial Ports)
Universal Serial Bus(moderate-speed, for connecting computers to peripherals)
Fibre Channel(high-speed, for connecting computers to mass storage devices)
InfiniBand(very high speed, broadly comparable in scope to PCI)
MIDIcontrol of electronic musical instruments
DMX512control of theatrical lighting
Serial Attached SCSI
SpaceWireSpacecraft communication network
*SONET and SDH (high speed telecommunication over optical fibers)
*T-1, E-1 and variants (high speed telecommunication over copper pairs)(see additional examples in
There are a number of serial communication standards which, while significantly at variance with the RS-232 standard, are casually and incorrectly called "RS-232".
List of device bandwidths
Comparison of synchronous and asynchronous signalling
Asynchronous serial communication
Parallel communication, to be contrasted with serial communication.
* [http://www.societyofrobots.com/microcontroller_uart.shtml Serial Interface Tutorial for Robotics] (contains many practical examples)
* [http://pinouts.ru/pin_SerialPorts.shtml Serial interfaces listing (with pinouts)]
* [http://c2.com/cgi/wiki?SerialPorts Wiki:SerialPorts]
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