Signaling - universal serial bus , Computer Engineering

Signaling - Universal Serial Bus:

USB supports following signaling rates:

o   A low speed rate of 1.5 Mbit/s is defined by USB 1.0. This is so much similar to "full speed" operation except each bit takes 8 times as long to transmit. It is intended primarily to save price in low-bandwidth human interface components (HID) such as mice, keyboards and joysticks.

o   A hi-speed (USB 2.0) rate of 480 M bit/s was introduced in the year2001. All hi-speed components are capable of falling  back  to  full-speed  operation  if  needed;  they  are  backward  compatible.  Connectors are identical.

o   The full speed rate of 12 Mbit/s is the fundamental USB data rate which is defined by USB 1.1. All USB hubs hold up full speed.

o   A Super Speed (USB 3.0) rate of 5.0 Gbit/s. The USB 3.0 requirement was released by Intel and partners in the year 2008, according to early reports from CNET news. The first USB 3 controller chips were sampled by NEC May  in the year 2009  [11] and generate by using the 3.0 specification are expected to arrive beginning in Q3 2009 and 2010.[12]  USB 3.0 connectors are usually backwards compatible, but include new wiring and full duplex operation. There is little incompatibility with older connectors.

USB signals are transmitted on a braided pair data cable having 90Ω ±15% Characteristic impedance,[13] labeled D- and D+ Prior to USB 3.0, These all collectively use in half-duplex differential signaling to reduce the effects of electromagnetic noise on longer lines. Transmitted signal levels are in the range 0.0-0.3 volts for low and in the range 2.8-3.6 volts for high in full speed (FS) and low speed (LS) modes, and -10-10 mV for low and 360-440 mV for high in hi- speed (HS) mode. In Full Speed mode the cable wires are not terminated, but in the HS mode has termination of 45 Ω to ground, or 90 Ω differentials to match the data cable impedance, by reducing interference of specific kinds. USB3.0 introduces 2 extra pairs of shielded twisted wire and new, mostly interoperable contacts in USB3.0 cables, for them. They allow the higher data rate, and also full duplex operation.

A USB connection  is  always  among a  host  or  hub at  the "A" connector  end,  and  a component  or  hub's "upstream" port at the other end. Initially, it was a "B' connector, saving from erroneous loop connections, but extra added upstream connectors were precise, and some cable vendors designed and sold cables which allowed erroneous connections (and potential damage to the circuitry). USB interconnections are not as perfect or as effortless as originally intended.

The host includes 15 kΩ pull-down resistors on each data line. While no device is connected, this pulls both data lines low into the so-called "single-ended zero" state (SE0 in the USB documentation), and mention a disconnected or reset connection.

A USB device pulls 1 of the data lines high having a 1.5 kΩ resistor. it overpowers 1 of the pull-down resistors in the host and leaves the data lines in an idle state which is called "J". For USB 1.x, the option of data line indicates a device's speed support; full-speed components pull D+ high, while low-speed devices pull D- high.

USB data is transmitted by toggling the data lines between the opposite K state and the J state. USB encodes data by using the NRZI convention; a 0 bit is transmitted by toggling the data lines from J to K or vice-versa, when a 1 bit is transmitted by leaving the data lines as-is. To ensure a minimum density of signal transitions USB uses bit stuffing technique; an extra 0 bit is inserted into the data stream after any appearance of 6 consecutive 1 bits. 7 consecutive 1 bits is all the time an error. USB 3.00 has included extra added data transmission encodings.

A USB packet starts with an 8-bit synchronization sequence 00000001. That is data lines toggle KJKJKJKK, after the initial idle state J. The final 1 bit (repeated K state) marks the end of the sync pattern and the starting of the USB frame.

A USB packet's end which is called EOP (end-of-packet), is specified by the transmitter driving 2 bit times of SE0 (D+ and D- both below max) and 1 bit time of J state. After this, the transmitter ceases to drive the D-/D+ lines and the aforementioned pull up resistors hold it in the J (idle) state. Sometimes skew due to reason of hubs may add as much as one bit time before the SE0 of the end of packet. This extra bit can be result in a "bit stuff violation" if the 6 bits before it in the CRC are '1's. This bit should be avoided by receiver.

A USB bus can reset by using a prolonged (10 to 20 milliseconds) SE0 signal.

Posted Date: 10/13/2012 7:42:54 AM | Location : United States







Related Discussions:- Signaling - universal serial bus , Assignment Help, Ask Question on Signaling - universal serial bus , Get Answer, Expert's Help, Signaling - universal serial bus Discussions

Write discussion on Signaling - universal serial bus
Your posts are moderated
Related Questions
What is the purpose of IOP. The purpose of IOP is to given an independent path way for transfer of information among external and internal memory.

Prolog Programming Language : Probably programming languages are procedural: than the programmer specifies exactly the right instructions (algorithms) required to get an agent

Describe the term- Macros A macro is a key or name which signifies a series of commands or key strokes. Many applications allow single nominated key or single word on a keyboar

What is difference between collaboration on task and event management? Web-based task management application let the user handle the multiple pieces and parts of large projects

Complementary metal oxide semiconductor (CMOS) refers to a chip inside your computer that saves your BIOS settings. As a result, the terms CMOS & BIOS are sometimes used interchang

The Concept of Parallel Execution and Concurrent Real world systems are obviously concurrent, and computer science is about modelling the actual world. Examples of actual worl

Explain the term - Instruction execution We  know  that  the  fundamental  function  performed  by  a  computer  is  the  execution  of  program. The program that is to be exec

Used to interrupt CPU normal implementation routine and to get its attention .Mostly generated by an external devices, timers, counters...etc

Q. Show the Noframes Tag? tag can be used for those browsers which aren't able to interpret tags. Even though most, if not all, of your visitors would

Define the term package- object oriented modeling A package is a common purpose mechanism for organising elements into groups. Package can also contain other packages. The no