Editing Serial communication

{{short description|Type of data transfer}}
{{more citations needed|date=August 2019}}
{{Use American English|date=May 2024}}

[[Image:Serial and Parallel Data Transmission.svg|class=skin-invert-image|thumb|right|300px|Serial and parallel data transmission of 01001011<sub>2</sub>. Standard bit sequence is least-significant-bit-first (D<sub>0</sub> to D<sub>7</sub> in ascending order).<ref name="Mackenzie_1980">{{cite book |url=https://textfiles.meulie.net/bitsaved/Books/Mackenzie_CodedCharSets.pdf |title=Coded Character Sets, History and Development |series=The Systems Programming Series |author-last=Mackenzie |author-first=Charles E. |date=1980 |edition=1 |publisher=[[Addison-Wesley Publishing Company, Inc.]] |isbn=978-0-201-14460-4 |lccn=77-90165 |pages=247–253 |access-date=2022-12-29 |archive-url=https://web.archive.org/web/20160526172151/https://textfiles.meulie.net/bitsaved/Books/Mackenzie_CodedCharSets.pdf |archive-date=May 26, 2016 |url-status=live |df=mdy-all }}</ref> D<sub>0</sub> is received first via serial transmission. All bits are received simultaneously via parallel transmission.]]

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.

[[Image:MIL-STD-188-100 char struct for async comms 1972-11-15.svg|class=skin-invert-image|thumb|right|400px|Standard character structure for asynchronous data communication consisting of 10 elements for a 7-bit ASCII character]]
Serial communication is used for all [[Long-haul communications|long-haul communication]] and most [[computer network]]s, where the cost of [[electrical cable|cable]] and difficulty of [[synchronization]] make parallel communication impractical. Serial computer buses have become 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]]) and to outstrip its disadvantages ([[clock skew]], interconnect density). The migration from [[Peripheral Component Interconnect|PCI]] to [[PCI Express]] (PCIe) is an example.

Modern high speed serial interfaces such as PCIe<ref>{{cite web |url=https://www.theregister.com/2022/01/12/final_pcie_60_specs_released/ |title=Final PCIe 6.0 specs unleashed: 64 GTps link speed incoming... with products to follow in 2023 |first=Dan |last=Robinson |date=12 January 2022 |website=[[The Register]]}}</ref><ref>{{cite web | url=https://www.anandtech.com/show/21335/full-draft-of-pcie-70-spec-available-512-gbs-over-pcie-x16-incoming | title=PCIe 7.0 Draft 0.5 Spec Available: 512 GB/S over PCIe x16 on Track for 2025 }}</ref><ref>{{cite web | url=https://arstechnica.com/gadgets/2022/01/pci-express-6-0-spec-is-finalized-doubling-bandwidth-for-ssds-gpus-and-more/ | title=PCIe 5.0 is just beginning to come to new PCS, but version 6.0 is already here | date=12 January 2022 }}</ref>  send data several bits at a time using modulation/encoding techniques such as [[PAM4]] which groups 2 bits at a time into a single symbol, and several symbols are still sent one at the time. This replaces PAM2 or non return to zero (NRZ) which only sends one bit at a time, or in other words one bit per symbol.<ref>{{cite book | url=https://books.google.com/books?id=wnGDBAAAQBAJ&dq=serial+pam4+signals&pg=PA9 | isbn=978-0-12-800671-9 | title=Handbook of Serial Communications Interfaces: A Comprehensive Compendium of Serial Digital Input/Output (I/O) Standards | date=21 August 2015 | publisher=Newnes }}</ref><ref>{{cite web | url=https://www.signalintegrityjournal.com/articles/1151-pam4-for-better-and-worse | title=PAM4: For Better and Worse &#124; 2019-02-26 &#124; Signal Integrity Journal }}</ref><ref>{{cite web | url=https://semiengineering.com/knowledge_centers/communications-io/off-chip-communications/pam-4-signaling/ | title=PAM-4 Signaling }}</ref><ref>{{cite conference |url=https://www.xilinx.com/publications/events/designcon/2016/slides-pam4signalingfor56gserial-zhang-designcon.pdf |title=PAM4 Signaling for 56G Serial Link Applications − A Tutorial |first1=Hongtao |last1=Zhang |first2=Brandon |last2=Jiao |first3=Yu |last3=Liao |first4=Geoff |last4=Zhang |conference=DesignCon 2016}}</ref><ref>{{cite web |url=https://download.tek.com/document/PAM4-Signaling-in-High-Speed-Serial-Technology_55W-60273.pdf |title=PAM4 Signaling in High-Speed Serial Technology: Test, Analysis, and Debug |type=application note |publisher=[[Tektronix]]}}</ref><ref>{{cite book | url=https://books.google.com/books?id=JljBDwAAQBAJ&dq=pam4+symbol&pg=PA54 | isbn=978-3-03921-792-2 | title=Advanced DSP Techniques for High-Capacity and Energy-Efficient Optical Fiber Communications | date=3 December 2019 | last1=Pan | first1=Zhongqi | last2=Yue | first2=Yang }}</ref><ref>{{cite book | url=https://books.google.com/books?id=MlruDwAAQBAJ&dq=pam4+symbol&pg=PA944 | isbn=978-1-119-52149-5 | title=Essentials of Modern Communications | date=4 August 2020 | publisher=John Wiley & Sons }}</ref><ref>{{cite journal |url=https://www.researchgate.net/figure/Eye-diagrams-of-PAM-2-4-8-with-normalized-vertical-full-swing-level-Peak-to-peak-swings_fig2_361960252 |title=Design Space Exploration of Single-Lane OFDM-Based Serial Links for High-Speed Wireline Communications |first=Gain |last=Kim |at=Figure 2 |journal=IEEE Open Journal of Circuits and Systems |issn=2644-1225 |volume=3 |issue=1 |date=January 2022 |doi=10.1109/OJCAS.2022.3189550|doi-access=free }}</ref> The symbols are sent at a speed known as the symbol rate or the baud rate.<ref>{{cite web | url=https://www.edn.com/eye-diagrams-the-tool-for-serial-data-analysis/ | title=Eye diagrams: The tool for serial data analysis | date=4 June 2019 }}</ref><ref>{{cite web | url=https://www.rfwireless-world.com/Terminology/Advantages-and-disadvantages-of-PAM4-modulation.html | title=Advantages of PAM4 modulation &#124; Disadvantages PAM4 signaling }}</ref><ref>{{cite web | url=https://www.edn.com/generate-pam4-signals-for-receiver-compliance-testing/ | title=Generate PAM4 signals for receiver compliance testing | date=20 September 2016 }}</ref><ref>{{cite book | url=https://books.google.com/books?id=L1YIEQAAQBAJ&dq=pam4+symbol+rate&pg=PA16 | isbn=978-1-040-01179-9 | title=Complex Digital Hardware Design | date=9 May 2024 | publisher=CRC Press }}</ref>

==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 port (hardware)|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 also mostly serial—such as [[coax cable]] plugged into a [[HD-SDI]] port, a [[webcam]] plugged into a USB port or [[IEEE 1394|FireWire port]], [[Ethernet cable]] connecting an [[IP camera]] to a [[Power over Ethernet]] port, [[FPD-Link]], digital telephone lines (ex. [[ISDN]]), etc.

Other such cables and ports, transmitting data one bit at a time, include [[Serial ATA]], [[SCSI connector#Serial SCSI|Serial SCSI]], Ethernet cable plugged into [[Ethernet port]]s, the [[Display Data Channel]] using previously reserved pins of the [[VGA connector]] or the [[DVI port]] or the [[HDMI]] port.

==Serial buses==
[[File:DB25 Diagram.svg|class=skin-invert-image|thumb|[[RS-232]] connector ([[D-Sub]] DB-25 variant)]]
Many communication systems were generally designed to connect two integrated circuits on the same [[printed circuit board]], connected by [[signal trace]]s on that board (rather than external cables).

[[Integrated circuit]]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 lower-speed serial buses include [[RS-232]], [[Digital Addressable Lighting Interface|DALI]], [[Serial Peripheral Interface Bus|SPI]], [[CAN bus]], [[I²C]], [[UNI/O]], and [[1-Wire]]. Higher-speed serial buses include [[USB]], [[SATA]] 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. The rationale for parallel communication was the added benefit of having [[Direct Memory Access]] to the 8-bit or 16-bit registry addresses at a time where mapping direct data lanes was more convenient and faster than synchronizing data serially.{{cn|date=May 2024}}

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). This can be caused by mismatched wire or conductor lengths.<ref name="cse378-lecture-24">{{cite web |url=https://courses.cs.washington.edu/courses/cse378/11wi/lectures/lec24.pdf |title=Lecture 24 |work=CSE378: Machine Organization & Assembly Language}}</ref><ref>{{cite book | url=https://books.google.com/books?id=BxptEAAAQBAJ | title=Modern Computer Architecture and Organization: Learn x86, ARM, and RISC-V architectures and the design of smartphones, PCS, and cloud servers | isbn=978-1-80323-823-4 | last1=Ledin | first1=Jim | last2=Farley | first2=Dave | date=4 May 2022 | publisher=Packt Publishing }}</ref>
*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.<ref name="cse378-lecture-24" />
*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.

The transition from parallel to serial buses was allowed by [[Moore's law]] which allowed for the incorporation of SerDes in integrated circuits.<ref>{{cite book | url=https://books.google.com/books?id=aUCgNOpyUbgC&dq=parallel++serial++serdes+moore%27s+law&pg=PA275 | isbn=978-1-4020-7496-7 | title=The Boundary — Scan Handbook | date=30 June 2003 | publisher=Springer }}</ref>
An electrical serial link only requires a pair of wires, whereas a parallel link requires several. Thus serial links can save on costs (also known as the [[Bill of Materials]]). [[Differential signalling]] uses length-matched wires or conductors and are used in high speed serial links.<ref>{{cite book | url=https://books.google.com/books?id=BxptEAAAQBAJ | title=Modern Computer Architecture and Organization: Learn x86, ARM, and RISC-V architectures and the design of smartphones, PCS, and cloud servers | isbn=978-1-80323-823-4 | last1=Ledin | first1=Jim | last2=Farley | first2=Dave | date=4 May 2022 | publisher=Packt Publishing }}</ref> Length-matching is easier to perform on serial links as they require fewer conductors.

In many cases, serial is cheaper to implement than parallel. Many [[Integrated circuit|IC]]s have serial interfaces, as opposed to parallel ones, so that they have fewer pins and are therefore less expensive.

==Examples of architectures==
{{Div col|colwidth=30em}}
*[[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 bus|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]]
*[[Fiber Distributed Data Interface]]
*[[Fibre Channel]] (high-speed, for connecting computers to mass storage devices)
*[[FireWire]]
*[[HDMI]]
*[[HyperTransport]]
*[[InfiniBand]] (very high speed, broadly comparable in scope to [[Peripheral Component Interconnect|PCI]])
*[[I²C]] multidrop serial bus
*[[MIDI]] control of electronic musical instruments
*[[MIL-STD-1553|MIL-STD-1553A/B]]
*[[Morse code]] [[telegraphy]]
*[[PCI Express]]
*[[Profibus]]
*[[RS-232]] (low-speed, implemented by [[serial port]]s)
*[[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 [[Synchronous Optical Networking|SDH]] (high speed telecommunication over optical fibers)
*[[SpaceWire]] Spacecraft communication network
*[[S/PDIF]] and [[AES3]] audio communication protocols
*[[Serial Peripheral Interface Bus|SPI]]
*[[T-carrier|T-1]], [[E-carrier|E-1]] and variants (high speed telecommunication over copper pairs)
*[[Universal Serial Bus]] (for connecting peripherals to computers)
*[[UNI/O]] multidrop serial bus
*[[1-Wire]] multidrop serial bus
{{Div col end}}

==See also==

* [[8N1]]
* [[Asynchronous serial communication]]
* [[Comparison of synchronous and asynchronous signalling]]
* [[Computer bus]]
* [[Data transmission]]
* [[Eye pattern]]
* [[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==
{{Reflist}}

==External links==
*[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: Serial Ports]
*[https://web.archive.org/web/20090226195855/http://www.thaiio.com/prog-cgi/VBnetSerialPort.htm Visual studio 2008 coding for Serial communication]
*[http://www.byteparadigm.com/kb/article/AA-00255 Introduction to I²C and SPI protocols] {{Webarchive|url=https://web.archive.org/web/20160308185505/http://byteparadigm.com/kb/article/aa-00255 |date=2016-03-08 }}
*[https://learn.sparkfun.com/tutorials/serial-communication/all Serial communication introduction]
*[https://training-kits.appspot.com/serial-linux.html Serial Port Programming in Linux] {{Webarchive|url=https://web.archive.org/web/20180702014758/http://training-kits.appspot.com/serial-linux.html |date=2018-07-02 }}

{{Computer-bus}}
{{Bit-encoding}}

[[Category:Serial buses| ]]
[[Category:Physical layer protocols]]