USB Universal Serial Bus Includes:
USB introductionUSB standardsConnectors, pinouts & cablesData transfer & protocolUSB 3USB-C
USB introductionUSB standardsConnectors, pinouts & cablesData transfer & protocolUSB 3USB-C
Page 3 Section 1. Important Safety Instructions READ AND FOLLOW ALL INSTRUCTIONS Lire la notice technique. All electrical work must be performed by a licensed electrician and conform to all national, state, and local codes.
USB, Universal Serial Bus is very easy to use providing a reliable and effective means of transferring data.
To achieve this the system has a defined data transfer protocol that enables the data to be formatted and carried in a defined way that provides the reliable communication.
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Although some changes have been made between the different updates to the USB standard, the protocol, signalling and data transfer modes are basically the same.
USB signalling and data transfer basics
For USB 1 and 2 a four wire system is employed. As detailed elsewhere, the cables carry: power, ground and then there is a twisted pair for the differential data transfer. The lines are designated data+ and data -.
The data uses an NRZI system, i.e. non-return to zero.In terms of operation, when the USB host powers up, it polls each of the slave devices in turn.
The USB host has address 0, and then assigns addresses to each device as well as discovering the slave device capabilities in a process called enumeration. [Enumeration also takes place when a new device is connected].
Transactions between the host and device comprise a number of packets. As there are several different types of data that can be sent, a token indicating the type is required, and sometimes an acknowledgement is also returned.
Each packet that is sent is preceded by a sync field and followed by an end of packet marker. This defines the start and end of the packet and also enables the receiving node to synchronise properly so that the various date elements fall into place.
There are four basic types of data transaction that can be made within USB.
- Control: This type of data transaction within the overall USB protocol is used by the host to send commands or query parameters. The packet lengths are defined within the protocol as 8 bytes for Low speed, 8-64 bytes for Full, and 64 bytes for High Speed devices.
- Interrupt: The USB protocol defines an interrupt message. This is often used by devices sending small amounts of data, e.g. mice or keyboards. It is a polled message from the host which has to request specific data of the remote device
- Bulk: This USB protocol message is used by devices like printers for which much larger amounts of data are required. In this form of data transfer, variable length blocks of data are sent or requested by the Host. The maximum length is 64-byte for full speed Devices or 512 bytes for high speed ones. The data integrity is verified using cyclic redundancy checking, CRC and an acknowledgement is sent. This USB data transfer mechanism is not used by time critical peripherals because it utilises bandwidth not used by the other mechanisms.
- Isochronous: This form of data transfer is used to stream real time data and is used for applications like live audio channels, etc. It does not use and data checking, as there is not time to resend any data packets with errors - lost data can be accommodated better than the delays incurred by resending data. Packet sizes can be up to 1024 bytes.
The data transfer methodology and protocol for USB provides an effective method of transferring the data across the interface in an effective and reliable manner.
Wireless & Wired Connectivity Topics:
Mobile Communications basics2G GSM3G UMTS4G LTE5GWiFiIEEE 802.15.4DECT cordless phonesNFC- Near Field CommunicationNetworking fundamentalsWhat is the CloudEthernetSerial dataUSBSigFoxLoRaVoIPSDNNFV
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Mobile Communications basics2G GSM3G UMTS4G LTE5GWiFiIEEE 802.15.4DECT cordless phonesNFC- Near Field CommunicationNetworking fundamentalsWhat is the CloudEthernetSerial dataUSBSigFoxLoRaVoIPSDNNFV
Return to Wireless & Wired Connectivity
Parallel versus serial communication.
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.
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 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) and to outstrip its disadvantages (clock skew, interconnect density). The migration from PCI to PCI Express is an example.
Cables[edit]
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 plugged into a USB port or Firewire port, Ethernet cable connecting an IP camera to a Power over Ethernet port, FPD-Link, 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[edit]
RS-232 connector.
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 serial buses include RS-232, SPI, I²C, DC-BUS, UNI/O, 1-Wire and PCI Express. In IC, serial bus may be typically implemented by using multiplexer (which utilizes technique called multiplexing).[1]
Serial versus parallel[edit]
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.
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.
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Examples of architectures[edit]
- ARINC 818 Avionics Digital Video Bus
- Atari SIO (Joe Decuir credits his work on Atari SIO as the basis of USB)
- CAN Control Area Network Vehicle Bus
- ccTalk Used in the money transaction and point-of-sale industry
- CoaXPress industrial camera protocol over Coax
- DC-BUS communication over DC power lines
- DMX512 control of theatrical lighting
- Fibre Channel (high-speed, for connecting computers to mass storage devices)
- InfiniBand (very high speed, broadly comparable in scope to PCI)
- I²C multidrop serial bus
- MIDI control of electronic musical instruments
- RS-232 (low-speed, implemented by serial ports)
- RS-422 multidrop serial bus
- RS-485 multidrop multimaster serial bus
- SDI-12 industrial sensor protocol
- SONET and SDH (high speed telecommunication over optical fibers)
- SpaceWire Spacecraft communication network
- T-1, 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
See also[edit]
- High-Level Data Link Control (HDLC)
- Universal asynchronous receiver/transmitter (UART)
References[edit]
- ^'Circuit Implementation Using Multiplexers'. www.ee.surrey.ac.uk. Retrieved 2019-04-30.
External links[edit]
- Serial Interface Tutorial for Robotics (contains many practical examples)
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