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USB Scanner And Printer Not Responding, or Loss Of Communications, Basic Overview

Discussion in 'Misc Electronics' started by Jerry G., Aug 4, 2004.

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  1. Jerry G.

    Jerry G. Guest

    There are many instances of people installing new scanners and printers on
    new systems using USB 2, and having "Not Responding" errors. The USB 1 ports
    are having less instances of this problem.

    The described problem can be very frustrating, and sometimes be very
    difficult to resolve. Many users would first start by uninstalling and
    reinstalling the software, when the software is not directly at fault.

    At the hardware level, and at the Windows test level, the device checks to
    be okay, and responding properly. Yet, it does not respond properly when
    doing its work.

    Some symptoms are that the scanner may stop in the middle of the scan and
    hang, or not scan at all. Or, a printer may stop in the middle of a page and
    hang. In the case of the printer, if it does not hang, it may start to print
    random looking characters during the middle of a print job.

    It turns out that with USB 2 ports, on many P4 machines this problem may
    occur with some scanners and printers. This has to do with several factors.

    If the USB Root Hub is IRQ shared with other devices that are particularly
    active, this problem may occur in many systems. This has to do with data
    streaming being interrupted (shared IRQ requests), and the receiving device
    becoming timed out. The device becomes out of sync. The device may then
    hang, or stop responding, and have to be reset.

    There is also the condition where the data inputs of the device being driven
    by the USB port are pulling peaks of too much peak current for the USB port
    to handle. Considering the speed of the data coming from the port, the
    effective impedance of the device load may be a bit low, thus causing it to
    pull more current than what the USB port can support.


    An easy fix for this condition, if in the event that the condition described
    here is relevant to the problem described, is to add an externally powered
    USB hub between the USB port and the unit that is having the loss of the
    normal responding condition.

    The external powered USB hub will act as a data and power buffer between the
    device, and the computer's USB port. In this case it is effectively acting
    as an extended USB data port, with its own independent port power drive.
    Because the USB hub will run slower than the port feeding it, there is the
    opportunity for it to continue streaming out the data during IRQ
    interruptions. The device being fed will normally not see these
    interruptions, unless they occurring for a longer time period than the
    streaming length from the hub.

    Connecting and using other devices to the same USB hub, may or may not cause
    any symptoms of loss, depending on the particular characteristics of the
    other devices sharing this USB hub, and the hub itself. This would be by
    trial and error.

    The proper fix would be for the manufactures to do some re-engineering of
    their products.

    Jerry G.
    Comments, and suggestions are welcome:

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