USB noise problem

If unplugging and replugging it fixes the issue, then can't you have a timeout in the 8051 s/w that does a detach/reattach if it doesn't receive anything from the host in a certain period of time?

Of course you really should fix this problem at the root cause, otherwise the detach/reattach/enumerate/initialize may happen in the middle of an operation with powered tools...!

If you can force the USB to operate at it's slowest mode (12Mbps?) you may get more noise immunity.

Bad idea. USB is flimsy interface intended for the tabletop conditions.

No wonder. This is what expected.

Because the USB software is developed in the assumption of the perfect communication link.

Then you have to develop all of the software and drivers yourself.

There is no good solution with USB. Use Ethernet.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

uses USB for

The C340 does not support high-speed USB (480 Mbps), so he's probably running at full speed (12 Mbps).

-a

Ground loops?

Hi, USB speed is 12 mbps. We are taking care at next hardware design to reduce the noise. But still I want to know one think, **** How can I detect USB link breaks (or Hang condition) ???? please give me any "link" to this problem and also PCB design guidelines to reduce noise problem.

Thanks & Regards, kishore.

The best site for USB info is:

or

Good paper on Board Layout issues

EMI issues

The device should no worry about loss of connectivity, beyond what the spec covers, which is part of the basic enumeration code that comes with the device. The device is a slave. If there are connectivity problems, it is up to the host to recognize that and handle them appropriately.

If the host hangs, the drivers or other software are improperly written. If this is Windows, your communication with the USB drivers should have timeouts in them.

Marco

The C340 does not support high-speed USB (480 Mbps), so he's probably running at full speed (12 Mbps).

-a

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We are using read files and write file function of windows API to access our USB devices based on Silab microcontroller. For these functions there are timeout setting but these setting can be used for com ports and not for any other IO devices. So whenever we called read file function and the USB device does not responds, then application hangs. since software does not return from read file function we need to disconnect USB device to make read file function return error ie. "USB device not found" Please suggest any solution for this problem.

Thanks & Regards, Kishor.

The big difference between a real serial port and a USB port is that USB serial ports can fail at any time. Consequently you must poll the serial port using ClearCommError() before every read and you must never request more data than is available. You need to look at both the error code and the status block.

It's a real pain, but it works. I'm sure that there's a better way using asynchronous modes, but I had to update an existing app.

Stephen