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In USB why VID(vendor id) , PID(Product id ) are required??

harshan

Greetings,

               i am just beginner of USB as initial steps i read USB 2.0 Specification document, one thing i don't understand that why the VID(vendor id), PID(product id) is needed?? as in enumaration after connecting the USB device to the host, the host will send the reset signal then the device will repond to that reset signal. after that the usb will send unique id/address to the device and  that address the device should have to store in corresponding appropriate field. after that the host will request to the  device about descriptor like(device,configuration,string,endpoint....etc), as a response for that the device will transmit the descriptor filled structure. In device descriptor i observed that there will be a vid and pid field which will be assigned by USB-IF and product manufacturer my doubt was already the host send unique address/id to the device through which it will respond but why this VID and PID?? hope you clear about my question.

Thanks and Regards.

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  • 0 in reply to harshan

    I am not sure but trying to guess - the unique address could be a per piece serial number kind of thing while the PID is same throughout for that product.

    For e.g. USB mouse model X manufactured by ABC will have the same PID for all production quantity of model X but for each manufactured model X, the serial number will be different.

    Sorry this is a wild guess at the moment.

    VID is the vendor ID, so it will be same for all products made by ABC.

  • 0 in reply to harshan

    Greetings,,

    I don't have that much experiance with USB but what gopal.amlekar says is true (VID refers to Vendor ID and PID refer to Product id) now back to your question

    Thanks for reply,

                             Then what will be  the use of unique id/address which will sent by the host to device after the host sent reset signal??

    I'm not sure about my answer but let's just imagine you bought the same product from the same compay (they will have the same PID and VID) how would the host distingush them now..?

    like what you said and gopal.amlekar said I guess that is the use of (unique id/address)

    Regards,,

    Mustafa S.