usb port connection

Discussion in 'Embedded Systems and Microcontrollers' started by opk.bob, Sep 19, 2012.

  1. opk.bob

    Thread Starter New Member

    Jul 18, 2012
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    i want to know how usb port connection is interface with usb device
    ie power to the device data input and output.
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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  3. sceadwian

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    Jun 1, 2009
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    You're in for a very very long read.
    The physical specification are quiet simple, the transfer protocol and enumeration methods required are.... Very complex. The USB 2.0 specification is over 650 pages long.

    Full specifications can be found here.
    http://www.usb.org/developers/docs/
     
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    <shrug> Never read it, but I've done several USB based apps.

    Of course, a good code library is my best friend.
     
  5. nigelwright7557

    Senior Member

    May 10, 2008
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    I have done 2 USB projects using readily available code as the basis.

    waitingforfriday.com has a few USB projects and supplies circuit diagrams and software.
     
  6. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    If the OP is trying to know about the power side of the USB connection, thats is not as difficult as the transactions involved.
     
  7. wmodavis

    Well-Known Member

    Oct 23, 2010
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  8. sceadwian

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    Jun 1, 2009
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    The article is also incorrect. The standard allowance for USB ports is 100ma before enumeration regardless of it's version, to get more power out of a port a bus protocol request must be made regardless of USB version. USB 3.0 and USB on the go apparently after enumeration allow up to 1.8amps to be drawn only for power usage, 1.5amps is the limit if the communication lines are still used and that's only for low speed communication. High speed prohibits anything more than 100ma on the power lines during communication

    Virtually every wall adapter and a large portion of USB root devices technically violate the USB specs when used as a charging port, and that doesn't even account for voltage variations.
     
  9. wmodavis

    Well-Known Member

    Oct 23, 2010
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    Would you please site a source for your information. If you are going to contridict an official source you should list credible evidence to back up your statement.
     
  10. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    The power is simply about 5 volts (usually between 4.8 and 5.2), and different versions are able to source different amounts of current. I once heard that 1.0 can source 100mA, 2.0 200mA, and 3.0 300mA, but I have since learned that it isn't that simple. But you get the idea, anyway.

    The device drivers you install on your computer are what read the data on the USB port and tell the computer what to do from there.
     
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