Forums

Multiple USB 1.1 devices in USB 2 Hub speed ?

Started by Anton Erasmus July 16, 2008
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.

Regards
  Anton Erasmus

On Jul 16, 12:07 pm, Anton Erasmus <nob...@spam.prevent.net> wrote:
> 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 ? >
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.
"Adrian" <adrianbica@yahoo.com> wrote in message 
news:c11ebd15-e7d7-4b6c-9a72-fac71de01b70@m3g2000hsc.googlegroups.com...
> On Jul 16, 12:07 pm, Anton Erasmus <nob...@spam.prevent.net> wrote: >> 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 ? >> > > 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
On Jul 16, 4:18 pm, "Peter Dickerson"
<firstname.lastn...@REMOVE.tesco.net> wrote:
> "Adrian" <adrianb...@yahoo.com> wrote in message > > news:c11ebd15-e7d7-4b6c-9a72-fac71de01b70@m3g2000hsc.googlegroups.com... > > > > > On Jul 16, 12:07 pm, Anton Erasmus <nob...@spam.prevent.net> wrote: > >> 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 ? > > > 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.
On Wed, 16 Jul 2008 21:18:30 +0100, "Peter Dickerson"
<firstname.lastname@REMOVE.tesco.net> wrote:

>"Adrian" <adrianbica@yahoo.com> wrote in message >news:c11ebd15-e7d7-4b6c-9a72-fac71de01b70@m3g2000hsc.googlegroups.com... >> On Jul 16, 12:07 pm, Anton Erasmus <nob...@spam.prevent.net> wrote: >>> 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 ? >>> >> >> 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.
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
On Jul 16, 5:41 pm, Anton Erasmus <nob...@spam.prevent.net> wrote:
> 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.
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.
> 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. >
The PC also should have more than one internal USB host controllers, if it is just a hub, it won't do the job.
> Regards > Anton Erasmus
Hello Anton,

> 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
Yes.
> Or does the USB 2 link fall back to a 1.1 compatible mode ?
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.
> 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.
You need one high speed port on your host and one high speed Hub with 6 downstream ports. Peter
Anton Erasmus ha scritto:
> 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 ?
yes, if the hub is " _multiple_ Transaction Translator" > Or does the USB 2 link fall back to a 1.1 compatible mode ? yes, if the hub is " _single_ Transaction Translator" regards
On Wed, 16 Jul 2008 16:55:14 -0700 (PDT), Adrian
<adrianbica@yahoo.com> wrote:

>On Jul 16, 5:41 pm, Anton Erasmus <nob...@spam.prevent.net> wrote: >> 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. > >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. > >> 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. >> > >The PC also should have more than one internal USB host controllers, >if it is just a hub, it won't do the job.
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
On Thu, 17 Jul 2008 09:23:42 +0200, "Peter Petersen" <pp@on-time.de>
wrote:

>Hello Anton, > >> 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 > >Yes. > >> Or does the USB 2 link fall back to a 1.1 compatible mode ? > >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. > >> 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. > >You need one high speed port on your host and one high speed Hub with 6 >downstream ports.
This is good news. Thanks for the info. Regards Anton Erasmus