In
telecommunication
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that ...
and
data transmission
Data transmission and data reception or, more broadly, data communication or digital communications is the transfer and reception of data in the form of a digital bitstream or a digitized analog signal transmitted over a point-to-point or ...
, serial communication is the process of sending
data
In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpret ...
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.
Serial communication is used for all
long-haul communication and most
computer network
A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are ...
s, where the cost of
cable and
synchronization
Synchronization is the coordination of events to operate a system in unison. For example, the conductor of an orchestra keeps the orchestra synchronized or ''in time''. Systems that operate with all parts in synchrony are said to be synchronou ...
difficulties make parallel communication impractical. Serial computer buses are becoming more common even at shorter distances, as improved
signal integrity and transmission speeds in newer serial technologies have begun to outweigh the parallel bus's advantage of simplicity (no need for serializer and deserializer, or
SerDes
{{Use American English, date = March 2019
A Serializer/Deserializer (SerDes) is a pair of functional blocks commonly used in high speed communications to compensate for limited input/output. These blocks convert data between serial data and paral ...
) and to outstrip its disadvantages (
clock skew, interconnect density). The migration from
PCI to
PCI Express is an example.
Cables
Many serial communication systems were originally designed to transfer data over relatively large distances through some sort of
data cable.
Practically all long-distance communication transmits data one bit at a time, rather than in parallel, because it reduces the cost of the cable. The cables that carry this data (other than "the" serial cable) and the
computer ports they plug into are usually referred to with a more specific name, to reduce confusion.
Keyboard and mouse cables and ports are almost invariably serial—such as
PS/2 port,
Apple Desktop Bus and
USB.
The cables that carry digital video are almost invariably serial—such as
coax cable plugged into a
HD-SDI port, a
webcam
A webcam is a video camera which is designed to record or stream to a computer or computer network. They are primarily used in videotelephony, livestreaming and social media, and security. Webcams can be built-in computer hardware or peripher ...
plugged into a USB port or
FireWire port,
Ethernet cable connecting an
IP camera
An Internet Protocol camera, or IP camera, is a type of digital video camera that receives control data and sends image data via an IP network. They are commonly used for surveillance, but, unlike analog closed-circuit television (CCTV) camera ...
to a
Power over Ethernet
Power over Ethernet, or PoE, describes any of several standards or ad hoc systems that pass electric power along with data on twisted-pair Ethernet cabling. This allows a single cable to provide both data connection and electrical power to ...
port,
FPD-Link
Flat Panel Display Link, more commonly referred to as FPD-Link, is the original high-speed digital video interface created in 1996 by National Semiconductor (now within Texas Instruments). It is a free and open standard for connecting the outpu ...
, etc.
Other such cables and ports, transmitting data one bit at a time, include
Serial ATA,
Serial SCSI, Ethernet cable plugged into
Ethernet ports, the
Display Data Channel using previously reserved pins of the
VGA connector or the
DVI port
Digital Visual Interface (DVI) is a video display interface developed by the Digital Display Working Group (DDWG). The digital interface is used to connect a video source, such as a video display controller, to a display device, such as a comp ...
or the
HDMI
High-Definition Multimedia Interface (HDMI) is a proprietary audio/video interface for transmitting uncompressed video data and compressed or uncompressed digital audio data from an HDMI-compliant source device, such as a display controlle ...
port.
Serial buses
Many communication systems were generally designed to connect two integrated circuits on the same
printed circuit board
A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a laminated sandwich str ...
, connected by
signal traces on that board (rather than external cables).
Integrated circuit
An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...
s are more expensive when they have more pins. To reduce the number of pins in a package, many ICs use a serial bus to transfer data when speed is not important. Some examples of such low-cost serial buses include
RS-232
In telecommunications, RS-232 or Recommended Standard 232 is a standard originally introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' ('' data terminal equipment'') suc ...
,
SPI,
I²C
I2C (Inter-Integrated Circuit, ), alternatively known as I2C or IIC, is a synchronous, multi-controller/multi-target (master/slave), packet switched, single-ended, serial communication bus invented in 1982 by Philips Semiconductors. It is wid ...
,
UNI/O,
1-Wire
1-Wire is a device communications bus system designed by Dallas Semiconductor Corp. that provides low-speed (16.3 kbit/s) data, signaling, and power over a single conductor.
1-Wire is similar in concept to I²C, but with lower data rates and ...
and
PCI Express.
Serial 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 simultaneously along multiple channels (e.g., wires, printed circuit tracks, or optical fibers); whereas, a serial link transmits only a single stream of data.
Although a serial link may seem inferior to a parallel one, since it can transmit less data per clock cycle, it is often the case that serial links can be clocked considerably faster than parallel links in order to achieve a higher data rate. Several factors allow serial to be clocked at a higher rate:
*
Clock skew between different channels is not an issue (for unclocked
asynchronous serial communication links).
*A serial connection requires fewer interconnecting cables (e.g., wires/fibers) and hence occupies less space. The extra space allows for better isolation of the channel from its surroundings.
*
Crosstalk is less of an issue, because there are fewer conductors in proximity.
*Budgets for power use, power dissipation, cable cost, component cost, IC die area, PC board area, ESD protection, etc. can be focused on a single link.
In many cases, serial is cheaper to implement than parallel. Many
ICs have serial interfaces, as opposed to parallel ones, so that they have fewer pins and are therefore less expensive.
Examples of architectures
*
ARINC 818 Avionics Digital Video Bus
*
Atari SIO (Joe Decuir credits his work on Atari SIO as the basis of USB)
*
Binary Synchronous Communications BSC - Binary Synchronous Communications
*
CAN Control Area Network Vehicle Bus
*
ccTalk Used in the money transaction and point-of-sale industry
*
CoaXPress industrial camera protocol over Coax
*
DMX512 control of theatrical lighting
*
Ethernet
Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 1 ...
*
Fibre Channel (high-speed, for connecting computers to mass storage devices)
*
FireWire
*
HDMI
High-Definition Multimedia Interface (HDMI) is a proprietary audio/video interface for transmitting uncompressed video data and compressed or uncompressed digital audio data from an HDMI-compliant source device, such as a display controlle ...
*
HyperTransport
HyperTransport (HT), formerly known as Lightning Data Transport, is a technology for interconnection of computer processors. It is a bidirectional serial/parallel high-bandwidth, low- latency point-to-point link that was introduced on April 2 ...
*
InfiniBand (very high speed, broadly comparable in scope to
PCI)
*
I²C
I2C (Inter-Integrated Circuit, ), alternatively known as I2C or IIC, is a synchronous, multi-controller/multi-target (master/slave), packet switched, single-ended, serial communication bus invented in 1982 by Philips Semiconductors. It is wid ...
multidrop serial bus
*
MIDI
MIDI (; Musical Instrument Digital Interface) is a technical standard that describes a communications protocol, digital interface, and electrical connectors that connect a wide variety of electronic musical instruments, computers, and ...
control of electronic musical instruments
*
MIL-STD-1553A/B
*
Morse code
Morse code is a method used in telecommunication to encode text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code is named after Samuel Morse, one ...
telegraphy
*
PCI Express
*
Profibus
*
RS-232
In telecommunications, RS-232 or Recommended Standard 232 is a standard originally introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' ('' data terminal equipment'') suc ...
(low-speed, implemented by
serial ports)
*
RS-422 multidrop serial bus
*
RS-423
*
RS-485 multidrop multimaster serial bus
*
SDI-12 industrial sensor protocol
*
SERCOM
*
Serial ATA
*
Serial Attached SCSI
*
Shift Register with serial-in and serial-out configuration
*
SONET and
SDH SDH may refer to:
Science, medicine and technology
* Serine dehydratase, an enzyme
* L-sorbose 1-dehydrogenase, an enzyme
* Succinate dehydrogenase, an enzyme
* Shubnikov–de Haas effect
* Social Determinants of Health, economic and social condit ...
(high speed telecommunication over optical fibers)
*
SpaceWire Spacecraft communication network
*
SPI
*
T-1,
E-1 and variants (high speed telecommunication over copper pairs)
*
Universal Serial Bus
Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply (interfacing) between computers, peripherals and other computers. A broad ...
(for connecting peripherals to computers)
*
UNI/O multidrop serial bus
*
1-Wire
1-Wire is a device communications bus system designed by Dallas Semiconductor Corp. that provides low-speed (16.3 kbit/s) data, signaling, and power over a single conductor.
1-Wire is similar in concept to I²C, but with lower data rates and ...
multidrop serial bus
See also
*
8N1
*
Asynchronous serial communication
*
Comparison of synchronous and asynchronous signalling
Synchronous and asynchronous transmissions are two different methods of transmission synchronization. Synchronous transmissions are synchronized by an external clock, while asynchronous transmissions are synchronized by special signals along the ...
*
Computer bus
*
Data transmission
Data transmission and data reception or, more broadly, data communication or digital communications is the transfer and reception of data in the form of a digital bitstream or a digitized analog signal transmitted over a point-to-point or ...
*
Federal Standard 1037C
*
High-Level Data Link Control (HDLC)
*
List of device bandwidths
*
MIL-STD-188
*
Serial Peripheral Interface Bus
*
Serial port
*
Synchronous serial communication
*
Universal asynchronous receiver/transmitter (UART)
References
External links
Serial Interface Tutorial for Robotics(contains many practical examples)
Serial interfaces listing (with pinouts)Wiki: Serial PortsIntroduction to I²C and SPI protocolsSerial communication introduction
{{Bit-encoding
Physical layer protocols