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USB 3.0/2.0 hub - mixed downstream combined to single upstream?

Jonathan Bender
Expert 7895 points
Other Parts Discussed in Thread: TUSB8040A1

Hello,


Looking at the TUSB8040A1 datasheet (four-port USB 3.0 hub), I see there is both a 'high-speed' (USB 2.0) and separate 'Super-Speed' (USB 3.0) upstream connection. Two questions:

1. If I wanted to leave the USB 2.0 upstream port disconnected, could this device (or some other TI USB device) 'convert' any downstream USB 1.1 / USB 2.0 signals to go over the upstream USB 3.0 connection?

2. On the same subject, if I leave the USB 2.0 upstream port disconnected, will any downstream USB 1.1 / USB 2.0 signals simply not be passed?

Thanks in advance for the help with these questions.

  • 0
    TI__Guru 60865 points

    Hi Jonathan,


    The USB 3.0 specification requires that hubs be connected to both the USB 3.0 and USB 2.0 portions of the bus to be compliant.  However, if USB 3.0 only was connected, only USB 3.0 devices would be seen, but of course, there would be no backwards compatibility.  There is no conversion between the USB 3.0 and USB 2.0 connections in a USB 3.0 hub.  A USB 3.0 hub is essentially two hubs in one device that operate almost independently of one another, with the exception of port power control.

    Regards,

    JMMN

  • 0 in reply to JMMN
    TI__Expert 7895 points

    Hi JMMN,

    Thank you very much for your fast reply. In the event that I did not want to connect the upsteam USB 2.0 data port, can I just leave those pins floating, or would some sort of termination be required? I didn't see any mention in the TUSB8040A1 datasheet.

     

    Thanks,

     

    Jonathan

  • 0 in reply to Jonathan Bender
    TI__Guru 60865 points

    Hi Jonathan,

    Since connecting USB 3.0 only is a non-compliant application, it is not something the TUSB80xx devices technically support.   It would likely work in a closed system, but in a real world application where there are BIOS drivers that load the USB tree in USB 2.0 and then swap to the USB 3.0 capable operating system drivers, you could see interoperability issues and other problems. 

    Regards,

    JMMN

  • 0 in reply to JMMN
    TI__Expert 7895 points

    Hi JMMN,

    Great, I understand. Thanks again for your quick (and in-depth) reply.

    Jonathan

  • 0 in reply to Jonathan Bender
    Genius 4025 points

    Thanks for the help guys.  Is there any part that you would recommend for the customer?  It kinda sounds like what he is trying to do is not possible. Is that correct?