Multiple USB 1.1 devices in USB 2 Hub speed ?

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

Briefly: 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.

And No, you don't get the 12 MB/s for each device. You still get 12 MB/s to share.

Peter

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.

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.

Regards Anton Erasmus

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.

Hello Anton,

Yes.

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

Anton Erasmus ha scritto:

yes, if the hub is " _multiple_ Transaction Translator"

yes, if the hub is " _single_ Transaction Translator"

regards

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 ?

Regards Anton Erasmus

This is good news.

Thanks for the info.

Regards Anton Erasmus

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 ?

Regards Anton Erasmus

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 controllers. 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.

Anton Erasmus ha scritto:

google (all words): usb hub multi TT

regards

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          | paul@pcserviceselectronics.co.uk
    PC Services
 Timing Diagram Font
  GNU H8 - compiler & Renesas H8/H8S/H8 Tiny
 For those web sites you hate