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 fe ...
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 o ...
, 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 interpreted ...
one
bit
The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represente ...
at a time, sequentially, over a
communication channel
A communication channel refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel in telecommunications and computer networking. A channel is used for informa ...
or
computer bus
In computer architecture, a bus (shortened form of the Latin '' omnibus'', and historically also called data highway or databus) is a communication system that transfers data between components inside a computer, or between computers. This ex ...
. This is in contrast to
parallel communication
In data transmission, parallel communication is a method of conveying multiple binary digits (bits) simultaneously using multiple conductors. This contrasts with serial communication, which conveys only a single bit at a time; this distinction i ...
, 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
Cable may refer to:
Mechanical
* Nautical cable, an assembly of three or more ropes woven against the weave of the ropes, rendering it virtually waterproof
* Wire rope, a type of rope that consists of several strands of metal wire laid into a hel ...
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
Signal integrity or SI is a set of measures of the quality of an electrical signal. In digital electronics, a stream of binary values is represented by a voltage (or current) waveform. However, digital signals are fundamentally analog in nature, ...
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 Clock skew (sometimes called timing skew) is a phenomenon in synchronous digital circuit systems (such as computer systems) in which the same sourced clock signal arrives at different components at different times due to gate or, in more advanced s ...
, interconnect density). The migration from
PCI
PCI may refer to:
Business and economics
* Payment card industry, businesses associated with debit, credit, and other payment cards
** Payment Card Industry Data Security Standard, a set of security requirements for credit card processors
* Pro ...
to
PCI Express
PCI Express (Peripheral Component Interconnect Express), officially abbreviated as PCIe or PCI-e, is a high-speed serial computer expansion bus standard, designed to replace the older PCI, PCI-X and AGP bus standards. It is the common ...
is an example.
Cables
Many serial communication systems were originally designed to transfer data over relatively large distances through some sort of
data cable
A data cable is any media that allows baseband transmissions (binary 1s and 0s) from a transmitter to a receiver.
Examples Are:
*Networking Media
**Ethernet Cables ( Cat5, Cat5e, Cat6, Cat6a)
**Token Ring Cables ( Cat4)
** Coaxial cable is some ...
.
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
The PS/2 port is a 6-pin mini-DIN connector used for connecting keyboards and mice to a PC compatible computer system. Its name comes from the IBM Personal System/2 series of personal computers, with which it was introduced in 1987. The PS/2 mo ...
,
Apple Desktop Bus
Apple Desktop Bus (ADB) is a proprietary bit-serial peripheral bus connecting low-speed devices to computers. It was introduced on the Apple IIGS in 1986 as a way to support low-cost devices like keyboards and mice, allowing them to be connect ...
and
USB
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 v ...
.
The cables that carry digital video are almost invariably serial—such as
coax cable
Coaxial cable, or coax (pronounced ) is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric ( insulating material); many coaxial cables also have a p ...
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 peripheral d ...
plugged into a USB port or
FireWire port
IEEE 1394 is an interface standard for a serial bus for high-speed communications and isochronous real-time data transfer. It was developed in the late 1980s and early 1990s by Apple in cooperation with a number of companies, primarily Sony an ...
,
Ethernet cable
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 198 ...
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) cameras, ...
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 d ...
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 output ...
, etc.
Other such cables and ports, transmitting data one bit at a time, include
Serial ATA
SATA (Serial AT Attachment) is a computer bus interface that connects host bus adapters to mass storage devices such as hard disk drives, optical drives, and solid-state drives. Serial ATA succeeded the earlier Parallel ATA (PATA) standard t ...
,
Serial SCSI
A SCSI connector ( ) is used to connect computer parts that use a system called SCSI to communicate with each other. Generally, two connectors, designated male and female, plug together to form a connection which allows two components, such as a ...
, Ethernet cable plugged into
Ethernet port
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 198 ...
s, the
Display Data Channel
The Display Data Channel, or DDC, is a collection of protocols for digital communication between a computer display and a graphics adapter that enable the display to communicate its supported display modes to the adapter and that enable the compu ...
using previously reserved pins of the
VGA connector
The Video Graphics Array (VGA) connector is a standard connector used for computer video output. Originating with the 1987 IBM PS/2 and its VGA graphics system, the 15-pin connector went on to become ubiquitous on PCs, as well as many monitors ...
or the
DVI port 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 controller, ...
port.
Serial buses
![DB25 Diagram](https://upload.wikimedia.org/wikipedia/commons/b/b8/DB25_Diagram.svg)
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 engineering, electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a L ...
, connected by
signal trace In electronics, a signal trace or circuit trace on a printed circuit board (PCB) or integrated circuit (IC) is the equivalent of a wire for conducting signals. Each trace consists of a flat, narrow part of the copper foil that remains after etching. ...
s 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'') such a ...
,
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 wide ...
,
UNI/O
The UNI/O bus is an asynchronous serial bus created by Microchip Technology for low speed communication in embedded systems. The bus uses a master/slave configuration, requiring one signal to pass data between devices. The first devices supp ...
,
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
PCI Express (Peripheral Component Interconnect Express), officially abbreviated as PCIe or PCI-e, is a high-speed serial computer expansion bus standard, designed to replace the older PCI, PCI-X and AGP bus standards. It is the common ...
.
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 Clock skew (sometimes called timing skew) is a phenomenon in synchronous digital circuit systems (such as computer systems) in which the same sourced clock signal arrives at different components at different times due to gate or, in more advanced s ...
between different channels is not an issue (for unclocked
asynchronous serial communication
Asynchronous serial communication is a form of serial communication in which the communicating endpoints' interfaces are not continuously synchronized by a common clock signal. Instead of a common synchronization signal, the data stream contai ...
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
In electronics, crosstalk is any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel. Crosstalk is usually caused by undesired capacitive, induc ...
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
The Serial Input/Output system, universally known as SIO, was a proprietary peripheral bus and related software protocol stacks used on the Atari 8-bit family to provide most input/output duties for those computers. Unlike most I/O systems of the e ...
(Joe Decuir credits his work on Atari SIO as the basis of USB)
*
Binary Synchronous Communications
Binary Synchronous Communication (BSC or Bisync) is an IBM character-oriented, half-duplex link protocol, announced in 1967 after the introduction of System/360. It replaced the synchronous transmit-receive (STR) protocol used with second gene ...
BSC - Binary Synchronous Communications
*
CAN
Can may refer to:
Containers
* Aluminum can
* Drink can
* Oil can
* Steel and tin cans
* Trash can
* Petrol can
* Metal can (disambiguation)
Music
* Can (band), West Germany, 1968
** ''Can'' (album), 1979
* Can (South Korean band)
Other
* C ...
Control Area Network Vehicle Bus
*
ccTalk
ccTalk (pronounced see-see-talk) is a serial protocol in widespread use throughout the money transaction and point-of-sale industry. Peripherals such as the currency detectors for coins and banknotes found in a diverse range of automatic payment ...
Used in the money transaction and point-of-sale industry
*
CoaXPress CoaXPress (CXP) is a digital interface standard developed for high speed image data transmission in machine vision applications.
The name is a portmanteau of 'express' (as in express train) and 'coaxial' to emphasize CoaXPress is faster than other ...
industrial camera protocol over Coax
*
DMX512
DMX512 is a standard for digital communication networks that are commonly used to control lighting and effects. It was originally intended as a standardized method for controlling stage lighting dimmers, which, prior to DMX512, had employed ...
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 198 ...
*
Fibre Channel
Fibre Channel (FC) is a high-speed data transfer protocol providing in-order, lossless delivery of raw block data. Fibre Channel is primarily used to connect computer data storage to servers in storage area networks (SAN) in commercial data cen ...
(high-speed, for connecting computers to mass storage devices)
*
FireWire
IEEE 1394 is an interface standard for a serial bus for high-speed communications and isochronous real-time data transfer. It was developed in the late 1980s and early 1990s by Apple in cooperation with a number of companies, primarily Sony an ...
*
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 controller, ...
*
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
InfiniBand (IB) is a computer networking communications standard used in high-performance computing that features very high throughput and very low latency. It is used for data interconnect both among and within computers. InfiniBand is also used ...
(very high speed, broadly comparable in scope to
PCI
PCI may refer to:
Business and economics
* Payment card industry, businesses associated with debit, credit, and other payment cards
** Payment Card Industry Data Security Standard, a set of security requirements for credit card processors
* Pro ...
)
*
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 wide ...
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 re ...
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 of ...
telegraphy
Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas p ...
*
PCI Express
PCI Express (Peripheral Component Interconnect Express), officially abbreviated as PCIe or PCI-e, is a high-speed serial computer expansion bus standard, designed to replace the older PCI, PCI-X and AGP bus standards. It is the common ...
*
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'') such a ...
(low-speed, implemented by
serial port
In computing, a serial port is a serial communication interface through which information transfers in or out sequentially one bit at a time. This is in contrast to a parallel port, which communicates multiple bits simultaneously in parallel. ...
s)
*
RS-422
RS-422, also known as TIA/EIA-422, is a technical standard originated by the Electronic Industries Alliance that specifies electrical characteristics of a digital signaling circuit. It was meant to be the foundation of a suite of standards that ...
multidrop serial bus
*
RS-423
RS-423, also known as TIA/EIA-423, is a technical standard originated by the Electronic Industries Alliance that specifies electrical characteristics of a digital signaling circuit. Although it was originally intended as a successor to RS-232C of ...
*
RS-485
RS-485, also known as TIA-485(-A) or EIA-485, is a standard defining the electrical characteristics of drivers and receivers for use in serial communications systems. Electrical signaling is balanced, and multipoint systems are supported. The st ...
multidrop multimaster serial bus
*
SDI-12 SDI-12 (Serial Digital Interface at 1200 baud) is an asynchronous serial communications protocol for intelligent sensors that monitor environment data. These instruments are typically low-power (12 volts), are used at remote locations, and usually ...
industrial sensor protocol
*
SERCOM
*
Serial ATA
SATA (Serial AT Attachment) is a computer bus interface that connects host bus adapters to mass storage devices such as hard disk drives, optical drives, and solid-state drives. Serial ATA succeeded the earlier Parallel ATA (PATA) standard t ...
*
Serial Attached SCSI
*
Shift Register
A shift register is a type of digital circuit using a cascade of flip-flops where the output of one flip-flop is connected to the input of the next. They share a single clock signal, which causes the data stored in the system to shift from one loc ...
with serial-in and serial-out configuration
*
SONET
Synchronous optical networking (SONET) and synchronous digital hierarchy (SDH) are standardized protocols that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from light-emitting diode ...
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 condi ...
(high speed telecommunication over optical fibers)
*
SpaceWire
SpaceWire is a spacecraft communication network based in part on the IEEE 1355 standard of communications. It is coordinated by the European Space Agency (ESA) in collaboration with international space agencies including NASA, JAXA, and RKA.
...
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
The UNI/O bus is an asynchronous serial bus created by Microchip Technology for low speed communication in embedded systems. The bus uses a master/slave configuration, requiring one signal to pass data between devices. The first devices supp ...
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
8-N-1 is a common shorthand notation for a serial port parameter setting or configuration in asynchronous mode, in which there is one start bit, eight (8) data bits, no (N) parity bit, and one (1) stop bit
Asynchronous serial communicat ...
*
Asynchronous serial communication
Asynchronous serial communication is a form of serial communication in which the communicating endpoints' interfaces are not continuously synchronized by a common clock signal. Instead of a common synchronization signal, the data stream contai ...
*
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 th ...
*
Computer bus
In computer architecture, a bus (shortened form of the Latin '' omnibus'', and historically also called data highway or databus) is a communication system that transfers data between components inside a computer, or between computers. This ex ...
*
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 o ...
*
Federal Standard 1037C
Federal Standard 1037C, titled Telecommunications: Glossary of Telecommunication Terms, is a United States Federal Standard issued by the General Services Administration pursuant to the Federal Property and Administrative Services Act of 1949, a ...
*
High-Level Data Link Control
High-Level Data Link Control (HDLC) is a bit-oriented code-transparent synchronous data link layer protocol developed by the International Organization for Standardization (ISO). The standard for HDLC is ISO/IEC 13239:2002.
HDLC provides both c ...
(HDLC)
*
List of device bandwidths
This is a list of interface bit rates, is a measure of information transfer rates, or digital bandwidth capacity, at which digital interfaces in a computer or network can communicate over various kinds of buses and channels. The distinction can ...
*
MIL-STD-188
MIL-STD-188 is a series of U.S. military standards relating to telecommunications.
Purpose
Faced with "past technical deficiencies in telecommunications systems and equipment and software…that were traced to basic inadequacies in the applicat ...
*
Serial Peripheral Interface Bus
The Serial Peripheral Interface (SPI) is a synchronous serial communication interface specification used for short-distance communication, primarily in embedded systems. The interface was developed by Motorola in the mid-1980s and has become a ...
*
Serial port
In computing, a serial port is a serial communication interface through which information transfers in or out sequentially one bit at a time. This is in contrast to a parallel port, which communicates multiple bits simultaneously in parallel. ...
*
Synchronous serial communication Synchronous serial communication describes a serial communication protocol in which "data is sent in a continuous stream at constant rate."
Synchronous communication requires that the clocks in the transmitting and receiving devices are ''synchr ...
*
Universal asynchronous receiver/transmitter
A universal asynchronous receiver-transmitter (UART ) is a computer hardware device for asynchronous serial communication in which the data format and transmission speeds are configurable. It sends data bits one by one, from the least significan ...
(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