Talk:USB hub
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[edit] usb hub powered by batteries
Does anyone make a battery powered usb hub, that will allow you to use a usb host that doesn't have power to talk to devices that are not self powered? Basically I'm asking for a battery self powered usb hub. —Preceding unsigned comment added by 66.202.48.225 (talk • contribs)
- dunno if anyone makes one as a single unit but you could always look at the power requirements of a USB hub that takes DC power and build a battery pack to go with it. Plugwash 23:36, 1 November 2005 (UTC)
The CyberPower CP-H420MP is a battery powered 4-Port USB Hub: http://www.cyberpowersystems.com/CPH420MP.asppdecat
[edit] usb 2.0 hubs
can a hub that doesn't support high-speed mode be compliant with the usb 2.0 specification? Plugwash 00:37, 3 January 2006 (UTC)
- yes, because the 2.0 specification is backwards compatible with previous specifications therefore a full-speed (1.1 compliant) hub is compliant with the 2.0 spec. You could theoretically build a full-speed hub with a tt in it, but I don't know there would be a point to doing so. SchmuckyTheCat 08:25, 3 January 2006 (UTC)
[edit] Maximum number of downstream ports, on a self-powered hub
What is the maximum number of Downstream ports, one can possibly implement on a self-powered USB hub device? (not using host supplied power) I've seen 4 & 7 ports hubs maximum, all which are bus-powered. Is there any place that can say for sure? I tried browsing the USB 2.0 Spec, but can't find the definition - unlimited, or if limited what is the limit? Maybe 8, since Port 0 would be the upstream port, which leaves 1-7 for downstreams.
~Robin
- I removed your email address so that it does not get spam harvested.
- The answer is "as many as you can power". You've got 500ma of power from the bus, the hub itself uses some. From there you can have as many devices as you can power up. Some HID devices use as little as 25ma. An important consideration is that many bus-powered hubs don't report correctly as bus powered. They report self-powered to the controller. Because of this, you can often plug a bus-powered hub into another bus-powered hub. This breaks the spec but if you really wanted to play a game of "how many bus powered devices can I have off one bus powered port" it allows more. SchmuckyTheCat 16:22, 30 July 2006 (UTC)
- Afaict from a compliant equipment point of view you are limited to 4 as usb allocates power in units of 100ma (so thats one unit for each downstream device and one for powering the hub). There isn't anything to stop hub vendors breaking the spec though. Plugwash 17:37, 30 July 2006 (UTC)
It seems like that maximum would be about 127 ports on a hub, based on the good main USB article. As a practical matter, it seems like you would assemble a large tree of 7-port hubs. Eight of them would be a full two levels, and offer 49 usable ports -- and a total of 24.5 amps if everything was working right. 69.87.200.138 22:55, 6 December 2006 (UTC)
[edit] what can be connected to a hub
Are there any guidelines as to which devices you can connect using a USB hub? I have a laptop with only two USB ports. I have a printer, mouse and cell phone and am thinking about connecting an external hard drive as well. It is my understanding that some devices have to be connected directly to the port and won't work when connected to a hub. Rebel69 13:41, 15 August 2006 (UTC)
- Its pretty much a case of suck it and see, there are three issues to be considered. Firstly the power issues mentioned above (the devices connected downstream of a compliant bus powered hub can only draw a total of 4 100ma units of power, a noncompliant bus powered hub may allow more and a self powered hub should only be limited by the hubs power supply system). Then there is the issue of buggy drivers (e.g. when i plugged my mplab ICD2 into my belkin USB2 hub and installed the drivers it bluescreened windows). Finally there is the issue of bus bandwidth, especially if the designers weren't carefully about transfer modes (this can also happen without a hub depending on the systems usb controller design). Plugwash 16:08, 15 August 2006 (UTC)
[edit] internal (PCI) vs. external USB Hub
Which USB Hub is recommended for a PC (Desktop, Windos XP) external or internal ? Thank you! chtzou 19:58, 18 August 2006 (UTC)
- If its actually connected to the PC via PCI then its not a hub its a seperate USB controller. A seperate controller will give better performance than a hub if you have lots of high bandwidth devices and may also be usefull if you have devices that don't get on with hubs otherwise its a waste of money.
- If its just drawing its power from the PCI slot and connected to the PC via usb then it will perform just the same as a self powered external hub. Plugwash 23:45, 18 August 2006 (UTC)
- Do such actually exist? 69.87.200.138 22:58, 6 December 2006 (UTC)
- Dunno, I've never seen one but there is no reason it couldn't be made. Plugwash 13:00, 7 December 2006 (UTC)
[edit] "Common knowledge" is not the same as "original research"
I took the Original Research tag off of the paragraph about noncompliance. For devices that don't announce themselves, see any of the USB-powered lights/lighters/vacuum cleaners. They just yoink the 5V power, without connecting anything to the signal pins. Most powered hubs are non-compliant. Even a high-end hub like the DUB-H7 has 7 ports, advertised at 500mA each (for 3.5A), but only a 3A power brick (and part of that power goes into powering the hub and losses too). By the specs given on DLink's web site, it simply cannot supply the claimed 3.5A. That's still one of the better ones. See reviews on newegg.com with people not being able to use USB drives with many so-called powered hubs. Hell. I've designed plenty of non-compliant devices myself. Of the cheap devices I've bought, I would guess the majority were non-compliant (this doesn't extend to fancy expensive things).
Cites are good, but not necessary if something is commonly known. —Preceding unsigned comment added by 68.160.158.59 (talk • contribs) 31 December 2007
- Please do not assume that random information is common knowledge. This certainly doesn't qualify. Chris Cunningham 01:54, 31 January 2007 (UTC)
[edit] "Length limitations"
i think it would be helpful to list the length limitation in greater detail. See "Cables and long-haul solutions" at http://www.usb.org/developers/usbfaq/
