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stevef56:
Can a host force a port to a particular speed?

I want to design an embedded system where the host, usb trasceiver, and hub are on a single board and are all 2.0 compliant. But I want to force the ports on the hub to comunicate at full speed, even if a high speed device is plugged in. I want to do this so I can provide port isolation,

Jan Axelson:
Use a 2.0 host that doesn't support high speed.

Not sure what you mean or what you want to accomplish by port isolation.

Jan

stevef56:
Hi,

As I understand it if the port is 2.0 compliant and you plug in a high speed device the port will run high speed. If you plug in a full speed device it will run full speed. But for some ports I only want to allow full speed so that I can electrically isolate the port. Analog devices makes an IC that will provide the isolation but it can only work at low and full speed. I need electrical isolation because this is a medical device and sensor will be plugged into the usb port that have patient contact. An even better solution would be isolation that includes high speed. But 480Mbits/sec is just too fast.

Steve

Jan Axelson:
Embedded hosts aren't required to support high speed.

See the OTG and Embedded Host Supplement. It's included in the zip file with the USB 2.0 spec.

Another option is to provide the isolation on the device side, downstream from the USB connection. See:

http://www.edn.com/contents/images/6347257.pdf

Jan

stevef56:
Thanks Jan,

I'll look at the article but I don't think I can isolate on the device side because the device will be an off the shelf item where we don't have control of the design.

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