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About powered by UNIVERSAL SEREYAL BUS

Barney Picket

Hai
Great Keil Forum Support Team.

How much currant could drive my USB port?
Kindly advice to avoid damaged for the usb port..if I'm not wrong the Voltage around 5 VDC and 4 VDC.

Regards
Jeckson

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  • 0 in reply to Tsuneo Chinzei

    In addition to above post,

    USB spec regulates that root hub (ie. PC USB port) and self-powered hub should supply five unit load (500 mA). Just bus-powered hub is limited to one unit load (100mA). Therefore, above accident occurs just on bus-powered hub.

    Hub answers to host about its power supply status with GetStatus( DEVICE ) request from the host. But most of hubs on the market always answer to the inquiry as self-powered, even when it is actually bus-powered. Just hubs with "USB logo" obey the rule. Therefore, above situation doesn't occur so often in the real world.

    In this reason, a custom device driver is rarely made to solve above problem.
    Manufacturers of high-power devices just write to their user's manual as follows,
    when user sees power-supply overflow warning dialog, connect the device to self-powered hub.

    Tsuneo

Reply
  • 0 in reply to Tsuneo Chinzei

    In addition to above post,

    USB spec regulates that root hub (ie. PC USB port) and self-powered hub should supply five unit load (500 mA). Just bus-powered hub is limited to one unit load (100mA). Therefore, above accident occurs just on bus-powered hub.

    Hub answers to host about its power supply status with GetStatus( DEVICE ) request from the host. But most of hubs on the market always answer to the inquiry as self-powered, even when it is actually bus-powered. Just hubs with "USB logo" obey the rule. Therefore, above situation doesn't occur so often in the real world.

    In this reason, a custom device driver is rarely made to solve above problem.
    Manufacturers of high-power devices just write to their user's manual as follows,
    when user sees power-supply overflow warning dialog, connect the device to self-powered hub.

    Tsuneo

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