Serial communication

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Serial and parallel data transmission of 010010112. Standard bit sequence is least-significant-bit-first (D0 to D7 in ascending order). D0 is received first via serial transmission. All bits are received simultaneously via parallel transmission. Serial and Parallel Data Transmission.svg
Serial and parallel data transmission of 010010112. Standard bit sequence is least-significant-bit-first (D0 to D7 in ascending order). D0 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.

Contents

Standard character structure for asynchronous data communication consisting of 10 elements for a 7-bit ASCII character MIL-STD-188-100 char struct for async comms 1972-11-15.svg
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 communication and most computer networks, where the cost of cable and synchronization difficulties 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 PCI to PCI Express is an example.

Modern high speed serial interfaces such as PCIe [2] [3] [4] 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. [5] [6] [7] [8] [9] [10] [11] [12] The symbols are sent at a speed known as the symbol rate or the baud rate. [13] [14] [15] [16]

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 also mostly serial—such as coax cable plugged into a HD-SDI port, a webcam plugged into a USB port or 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, Serial SCSI, Ethernet cable plugged into Ethernet ports, the Display Data Channel using previously reserved pins of the VGA connector or the DVI port or the HDMI port.

Serial buses

RS-232 connector (D-Sub DB-25 variant) DB25 Diagram.svg
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 traces on that board (rather than external cables).

Integrated circuits 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, DALI, 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.[ citation needed ]

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:

The transition from parallel to serial buses was allowed by Moore's law which allowed for the incorporation of SerDes in integrated circuits. [20] 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. [21] 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 ICs have serial interfaces, as opposed to parallel ones, so that they have fewer pins and are therefore less expensive.

Examples of architectures

See also

Related Research Articles

<span class="mw-page-title-main">Bus (computing)</span> System that transfers data between components within a computer

In computer architecture, a bus is a communication system that transfers data between components inside a computer, or between computers. This expression covers all related hardware components and software, including communication protocols.

<span class="mw-page-title-main">RS-232</span> Standard for serial communication

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 such as a computer terminal or PC, and a DCE, such as a modem. The standard defines the electrical characteristics and timing of signals, the meaning of signals, and the physical size and pinout of connectors. The current version of the standard is TIA-232-F Interface Between Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange, issued in 1997.

<span class="mw-page-title-main">SCSI</span> Set of computer and peripheral connection standards

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<span class="mw-page-title-main">USB</span> Standard for computer data connections

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<span class="mw-page-title-main">Network topology</span> Arrangement of a communication network

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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 data are represented as an electromagnetic signal, such as an electrical voltage, radiowave, microwave, or infrared signal.

<span class="mw-page-title-main">Universal asynchronous receiver-transmitter</span> Computer hardware device

A universal asynchronous receiver-transmitter is a peripheral 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 significant to the most significant, framed by start and stop bits so that precise timing is handled by the communication channel. The electric signaling levels are handled by a driver circuit external to the UART. Common signal levels are RS-232, RS-485, and raw TTL for short debugging links. Early teletypewriters used current loops.

<span class="mw-page-title-main">Expansion card</span> Circuit board for connecting to a computer system to add functionality

In computing, an expansion card is a printed circuit board that can be inserted into an electrical connector, or expansion slot on a computer's motherboard to add functionality to a computer system. Sometimes the design of the computer's case and motherboard involves placing most of these slots onto a separate, removable card. Typically such cards are referred to as a riser card in part because they project upward from the board and allow expansion cards to be placed above and parallel to the motherboard.

<span class="mw-page-title-main">Serial port</span> Communication interface transmitting information sequentially

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. Throughout most of the history of personal computers, data has been transferred through serial ports to devices such as modems, terminals, various peripherals, and directly between computers.

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<span class="mw-page-title-main">PCI Express</span> Computer expansion bus standard

PCI 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 motherboard interface for personal computers' graphics cards, capture cards, sound cards, hard disk drive host adapters, SSDs, Wi-Fi, and Ethernet hardware connections. PCIe has numerous improvements over the older standards, including higher maximum system bus throughput, lower I/O pin count and smaller physical footprint, better performance scaling for bus devices, a more detailed error detection and reporting mechanism, and native hot-swap functionality. More recent revisions of the PCIe standard provide hardware support for I/O virtualization.

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Electronic test equipment is used to create signals and capture responses from electronic devices under test (DUTs). In this way, the proper operation of the DUT can be proven or faults in the device can be traced. Use of electronic test equipment is essential to any serious work on electronics systems.

Serial Peripheral Interface (SPI) is a de facto standard for synchronous serial communication, used primarily in embedded systems for short-distance wired communication between integrated circuits.

<span class="mw-page-title-main">Parallel communication</span> Method of data transmission in which bits are conveyed in parallel

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<span class="mw-page-title-main">PS/2 port</span> 6-pin mini-DIN connector for connecting keyboards and mice to a PC compatible computer

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 mouse connector generally replaced the older DE-9 RS-232 "serial mouse" connector, while the PS/2 keyboard connector replaced the larger 5-pin/180° DIN connector used in the IBM PC/AT design. The PS/2 keyboard port is electrically and logically identical to the IBM AT keyboard port, differing only in the type of electrical connector used. The PS/2 platform introduced a second port with the same design as the keyboard port for use to connect a mouse; thus the PS/2-style keyboard and mouse interfaces are electrically similar and employ the same communication protocol. However, unlike the otherwise similar Apple Desktop Bus connector used by Apple, a given system's keyboard and mouse port may not be interchangeable since the two devices use different sets of commands and the device drivers generally are hard-coded to communicate with each device at the address of the port that is conventionally assigned to that device.

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<span class="mw-page-title-main">IEEE 1394</span> Serial bus interface standard, also known as 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 and Panasonic. It is most commonly known by the name FireWire (Apple), though other brand names exist such as i.LINK (Sony), and Lynx.

MOST is a high-speed multimedia network technology for the automotive industry. It can be used for applications inside or outside the car. The serial MOST bus uses a daisy-chain topology or ring topology and synchronous serial communication to transport audio, video, voice and data signals via plastic optical fiber (POF) or electrical conductor physical layers.

References

  1. ↑ Mackenzie, Charles E. (1980). Coded Character Sets, History and Development (PDF). The Systems Programming Series (1 ed.). Addison-Wesley Publishing Company, Inc. pp. 247–253. ISBN   978-0-201-14460-4. LCCN   77-90165. Archived (PDF) from the original on May 26, 2016. Retrieved December 29, 2022.
  2. ↑ https://www.theregister.com/2022/01/12/final_pcie_60_specs_released/
  3. ↑ "PCIe 7.0 Draft 0.5 Spec Available: 512 GB/S over PCIe x16 on Track for 2025".
  4. ↑ "PCIe 5.0 is just beginning to come to new PCS, but version 6.0 is already here". 12 January 2022.
  5. ↑ Handbook of Serial Communications Interfaces: A Comprehensive Compendium of Serial Digital Input/Output (I/O) Standards. Newnes. 21 August 2015. ISBN   978-0-12-800671-9.
  6. ↑ "PAM4: For Better and Worse | 2019-02-26 | Signal Integrity Journal".
  7. ↑ "PAM-4 Signaling".
  8. ↑ https://www.xilinx.com/publications/events/designcon/2016/slides-pam4signalingfor56gserial-zhang-designcon.pdf
  9. ↑ https://download.tek.com/document/PAM4-Signaling-in-High-Speed-Serial-Technology_55W-60273.pdf
  10. ↑ Pan, Zhongqi; Yue, Yang (3 December 2019). Advanced DSP Techniques for High-Capacity and Energy-Efficient Optical Fiber Communications. ISBN   978-3-03921-792-2.
  11. ↑ Essentials of Modern Communications. John Wiley & Sons. 4 August 2020. ISBN   978-1-119-52149-5.
  12. ↑ https://www.researchgate.net/figure/Eye-diagrams-of-PAM-2-4-8-with-normalized-vertical-full-swing-level-Peak-to-peak-swings_fig2_361960252
  13. ↑ "Eye diagrams: The tool for serial data analysis". 4 June 2019.
  14. ↑ "Advantages of PAM4 modulation | Disadvantages PAM4 signaling".
  15. ↑ "Generate PAM4 signals for receiver compliance testing". 20 September 2016.
  16. ↑ Complex Digital Hardware Design. CRC Press. 9 May 2024. ISBN   978-1-040-01179-9.
  17. ↑ https://courses.cs.washington.edu/courses/cse378/11wi/lectures/lec24.pdf
  18. ↑ Ledin, Jim; Farley, Dave (4 May 2022). Modern Computer Architecture and Organization: Learn x86, ARM, and RISC-V architectures and the design of smartphones, PCS, and cloud servers. Packt Publishing. ISBN   978-1-80323-823-4.
  19. ↑ https://courses.cs.washington.edu/courses/cse378/11wi/lectures/lec24.pdf
  20. ↑ The Boundary — Scan Handbook. Springer. 30 June 2003. ISBN   978-1-4020-7496-7.
  21. ↑ Ledin, Jim; Farley, Dave (4 May 2022). Modern Computer Architecture and Organization: Learn x86, ARM, and RISC-V architectures and the design of smartphones, PCS, and cloud servers. Packt Publishing. ISBN   978-1-80323-823-4.
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