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Multiple USB 1.1 devices in USB 2 Hub speed ?

Discussion in 'Embedded' started by Anton Erasmus, Jul 16, 2008.

  1. Hi,

    If I have a number of USB 1.1 devices plugged into a USB 2 Hub, can I
    get the full 12MB/s of each USB 1.1 device via the USB 2 link to a
    host ? Or does the USB 2 link fall back to a 1.1 compatible mode ?

    I am also looking for a Mini USB IP67 bulkhead connector. So far I
    have found something from Samtec, Bulgin and the mil circular D38999
    series, but all these options are very bulky. If I can get a similar
    sized connector that can take through 2 or 3 USB links, then it will
    not be so bad.

    Anton Erasmus
    Anton Erasmus, Jul 16, 2008
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  2. Anton Erasmus

    Adrian Guest

    Not sure what's your question, it is a bit confusing. The two
    statements around the OR are equivalent.

    High speed = 480 Mbps (USB 2.0)
    Full Speed = 12Mbps (USB 1.1)
    Low Speed = 1.5Mbps (USB 1.1)
    USB 2.0 is backward compatible, so is the hub. It should support a mix
    of devices.

    So, yes, you get the 12Mbps full speed AND yes, the USB 2 link falls
    back to 1.1.
    Adrian, Jul 16, 2008
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  3. And No, you don't get the 12 MB/s for each device. You still get 12 MB/s to

    Peter Dickerson, Jul 16, 2008
  4. Anton Erasmus

    Adrian Guest

    The 12 Mbps (not MB) is the bit speed, it is not the actual bandwidth
    consumed by a device. Usually devices consume more less than that. As
    long as the sum of the Bandwidth of each device is less than 12000, it
    is ok.
    It is the Host controller who manages the bandwidth and places the
    devices endpoints on proper frames. It also decides what to do when
    the Bandwidth was reached, but this has nothing to do with the
    presence of a 2.0 hub.
    Adrian, Jul 16, 2008
  5. Thanks, this what I needed to know. So if I need to combine 6 full
    speed devices into one High speed channel, I would need something with
    6 1.1 host ports and one 2.0 device port. Are there any chipsets
    available that does this kind of thing? I have six USB 1.1 devices
    (FTDI chips in FIFO mode) each needing to send data at 3 Mbps to
    a host PC. The PC has 6 USB ports, but I need to take these through a
    sealed bulkhead, and the connectors I can get is to big to fit 6 of
    them. So I either need to get smaller IP-67 sealed USB connectors, or
    a way to combine the data into a single channel. I might be able to
    fit 2 USB connectors in which case the Full Speed limit per channel
    should be OK.

    Anton Erasmus
    Anton Erasmus, Jul 16, 2008
  6. Anton Erasmus

    Adrian Guest

    Basically, yes, but you need 2 host controllers to take care of those
    this devices, one would not be enough, because of the high bandwidth
    ( 6 x 3Mbps). This should be two independent controllers, not a
    controller with 2 ports, those just have an internal (root) hub. And
    be sure the 2.0 device controller is a real 2.0, many controllers
    pretend they are 2.0 but limited to full speed.
    The PC also should have more than one internal USB host controllers,
    if it is just a hub, it won't do the job.
    Adrian, Jul 17, 2008
  7. Hello Anton,
    No. It would do that with a full speed Hub, but not with a high speed
    (2.0) Hub.

    All the other posts in this thread are wrong. A USB 2.0 hub is an
    intelligent device which will repack the high speed communication coming
    from the host and resend it as full/low speed on its downstream ports.

    If you want to read about the details, see sections 11.1.1 and 11.14 of the
    USB 2.0 Spec (Hub Transaction Translator). USB 2.0 Hubs must be able to
    translate between high speed hosts and low/full speed donwstream devices.
    You need one high speed port on your host and one high speed Hub with 6
    downstream ports.

    Peter Petersen, Jul 17, 2008
  8. Anton Erasmus

    lowcost Guest

    Anton Erasmus ha scritto:
    yes, if the hub is " _multiple_ Transaction Translator"
    yes, if the hub is " _single_ Transaction Translator"

    lowcost, Jul 17, 2008
  9. Thanks, I did not think of this. Is an internal USB hub the norm for
    PCs, or is it normally more than one host controller ?

    Anton Erasmus
    Anton Erasmus, Jul 17, 2008
  10. This is good news.

    Thanks for the info.

    Anton Erasmus
    Anton Erasmus, Jul 17, 2008
  11. I have never seen this on the spec sheet of a USB Hub. Not that one
    get much in the way of documentation with these type of products.
    Are there any reputable manufacturers of USB hubs which gives these
    sort of specs, and which wil operate from -20 deg C to 85 deg C ?

    Anton Erasmus
    Anton Erasmus, Jul 17, 2008
  12. Anton Erasmus

    Adrian Guest

    Usually, computers have more than one USB controllers. You can see
    this in Device Manager, under USB Controllers section. The host
    controllers are listed there, as well as the root hubs, normally one
    per controller. Have to find the link between connectors and
    However, the other answers are correct, a 2.0 Hub will convert the
    speed from Full to High. (Sorry for misinformation, what I was saying
    is true for Full speed hubs, they use the actual speed of the device.
    I didn't play too much with 2.0 hubs. My bad.) In this case looks like
    you can use a hub and do not worry about speed because it is
    translated to High speed. Not sure if you can find a 2.0 hub with 6
    ports, and I'm not sure if the hub has a host controller for each port
    or uses one for all (which will give you the same bandwidth problem).
    But, if you use 2 hubs with 3 devices on each, that would be ok.
    Adrian, Jul 17, 2008
  13. Anton Erasmus

    lowcost Guest

    Anton Erasmus ha scritto:
    google (all words): usb hub multi TT

    lowcost, Jul 17, 2008
  14. Not that difficult to do your own!

    Look at NXP ISP1520 4 port Multiple transaction USB2.0 hub in ONE device.
    They also do a SEVEN port device. This would suit person with 6 x FTDI
    devices. You would have to check temp specs, myu spec says -40 to +70,
    but find out if they do an industrial/automotive grade part.

    ISP1520 can be used with no EEPROM or anything much else. Made a 3 port
    one from it for one design where it was on board with rest of circuitry.
    One of the ports was a permanently connected FTDI device.

    Paul Carpenter |
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    Paul Carpenter, Jul 17, 2008
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