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U4xx Troubleshooting


The U4xx must enumerate properly. That is, the operating system must correctly detect the device before you can control it. Confirm that the device is part of the hardware that has been detected. Under windows you would use the Control Panel ⁄ System utility to verify the detection.

Host Hardware Issues

Some USB host chip sets have difficulty with a wide range of USB devices. Specifically the older VIA chip set may not detect the U4xx. You could remove the VIA drivers and use the Microsoft-provided drivers. This will help in some HW configurations. Another alternative is to purchase a USB plug-in card.

The VIA drivers may install an "Enhanced USB Root Hub". Disabling this, but still allowing "USB Root Hub Companions" may also allow the USB device to be recognized.

The "SiS" chip sets are also known to have problems detecting a number of USB devices.

You may wish to look to to resolve many consumer USB issues.

App Code Verification

Please feel free to use the application example code to confirm the operation of the U4xx device.

Hardware:  U401 USB Interface    U421 USB Interface   U451 USB Interface

Programming:  USBm DLL Programming    Download Files

Application Notes:  U4x1 Application Notes    Misc Applications and Information    FAQ

While every effort has been made to make sure that the information posted on this site is correct, the author can not be held liable for any damages whatsoever for losses as a result of the application of this information. Use this information at your own risk.

USBmicro can design your custom and semi-custom USB product. Email about USB design can be directed to " Robert " at

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