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Microcontrollers USB (UNIVERSAL SERIAL BUS)

HISTORY:

appeared before the USB (universal serial port), peripherals, serial and parallel ports used, then raised the idea of \u200b\u200bcreating a universal port Input, Output (I / O), the first USB was created in 1996 by companies IBM, Intel , Northern Telecom, Compaq, Microsoft , Digital Equipment Corporation and NEC, this first USB 1.1, had a data communication speed of 1.5Mbps for peripherals such as keyboard, mouse, and 12 Mbps joyticks to full speed, while the USB 2.0 connector, was developed by companies: Hewlett-Packard, Intel, Lucent, Microsoft, NEC and Philips, which has a speed of 480 Mbps

USB t ork as an interface for transmitting data and distribution of energy in the current deals in almost all the peripherals for PCs, has been increased due to its transmission rate, because it improves the serial, parallel devices.

FEATURES

In general, USB is a standard that allows up to 127 peripheral devices (I / O), from a single connector, it shows better in PCs. its goal is to reduce the shortcomings of RS-232 serial port, which has a speed of 115 Kbps and the parallel port, one disadvantage is that these ports can connect only one device. One advantage of USB is that you can add devices without powering down the PC or device you are connecting.

There are two types of ports:

· USB 1.1: transfer has two speeds: 1.5 Mbps for keyboards, mouse, joysticks, etc.., and 12 Mbps full speed, for other devices.

· USB 2.0: was this type of connector is a high speed, supports a data transfer of 480 Mbps

USB devices consist of a differential transmitter, receiver differential S / E with which it can transmit and detect several different electrical states on the line, they include:

·  Transmission / Front Differential bits: are DIFF0 and DIFF1 states, called also J and K states

·  SE0 (Single-Ended 0): consists of the pin D + and D-, which connected to GND (ground), these terminals are used to detect the cone nection / disconnection of devices to indicate the EOP (end of packet) and to generate a reset.

·  IDLE: is the resting state or high impedance, allowing half-duplex transfer, detection of connection and disconnection of devices and the decriminalization (separate) came devices and FS and LS.

·  PCOS (top package) is indicated by a transition to IDLE K.

·  EOP (end of packet) is indicated by a sequence SE0 (2 bits) + J (1 bit) + IDLE.

·  device detection and discrimination FS / LS : when the transm ISOR leaves the line in IDLE If a device is connected its polarization state force J (DIFF0 if DIFF1 if LS or FS), and if not there, the polarization state of the transmitter power SE0.

·  Reset: SE0 transmission for> = 10 ms.

TYPES OF TRANSMISSION VIA THE USB

· Transmission asynchronous : Used for variable data flow

· isochronous transmission : Used for real-time, a steady stream of data is useful in audio applications, telephony and video.

· Transmission blocks (bulk) : The devices used to receive and send large amounts of information, with asynchronous devices such as printers, scanners, cameras (still photography, etc.).

· Transmission Control : Used for configuration and control of devices to manage the bus or channel.

· interrupt transmission : Used to transfer little data low non-recurrent and is often used in slow devices, such as mouse

TRANSACTIONS ARE MADE UP OF 3 PHASES:

Token, Data and Validation (Handshake):

Ø Phase Token: package consists of a token sent by the USB controller is always present in every transaction. The package contains the following fields:

· PID (packet identifies the type.) Protected by redundant bits,

· destination element address (7 bits + 4 bits device within the device element), and CRC5.

Ø Phase Data: (optional) Comprised of data packets that are transferred between the USB controller and the device. Each package consists of the fields PID, Data and CRC16.

Ø Validation Phase: (optional) used to indicate the result of the transaction. Composed of only a PID field.

USB connector portion

There are three types of connectors, no matter what, they all have the same pins and each pin of a different kind, has the same functions. Below is the design of the types of USB and description.