How to Check USB Device and USB Hub Power Issues and Limitations
How to Check USB Device and USB Hub Power Issues and Limitations
If you’re having USB problems, you can also refer to
=> [post=752196]How to Check Hardware / Connection Issues with your USB Device[/post]
=> [post=720762]Troubleshoot: Windows Won't Recognize Your USB Hard Drive[/post]
USB Overview
Host Controllers
The host is a PC or other computer that contains both a host controller and root hub. The host controller and root hub work together to allow Windows to communicate with devices on the computer's USB data bus. The host controller
=> Formats data for transmitting on the USB bus
=> Translates received data to a format that Windows can understand
=> Performs other functions related to managing communications on the USB bus
Hubs
Hubs have several important functions
A root hub is "inside" of your computer. Each root hub provides for one or more of the USB ports provided on your computer itself. A root hub, in combination with the host controller
=> Detects when you attach or remove a USB hardware device (and is what reports the hardware detection/change to Windows)
=> Carries out requests from the host controller
=> Passes data between devices on the USB data bus and the host controller.
USB Hubs and Devices Overview
USB devices
=> May draw some or all of their power from a USB port
=> All devices attached to the
same USB port must share the power available from the port
USB Hubs
=> One normally thinks of a USB hub as being external to the computer but computers also have internal hubs
(one per controller)
=> The
internal hubs appear in Device Manager listed as "Root" hubs
=> The
external hubs appear in Device Manager listed as "Generic hubs". They are user configurable
Root vs. Generic Hubs
USB Hubs appear in Device Manager when they’re connected
=> Internal hubs are normally listed as Root Hubs
=> External hubs are normally listed as Generic Hubs
Hubs expand the number of USB ports available on a computer and are responsible for providing and managing the power to USB ports[/I]
Generic Hub may also appear in Device Manager when you add a device that comes with integrated USB ports and therefore also acts as a hub (e.g. some keyboards and monitors come with integrated USB ports)
Self-Powered vs Bus-Powered Hubs
Hubs can be either bus-powered, drawing power directly from the USB bus, or self-powered, drawing power from an external AC adapter
- Bus-powered hubs can provide up to 100 milliamperes (mA) of power per port. They can power a maximum of four ports
- Self-powered hubs, on the other hand, typically provide up to 500 mA of power per port. They can provide power for more than four ports
USB Voltage Requirements
Voltage supplied by a host or a powered hub ports must be between 4.75 V and 5.25 V
=> If you're having USB issues and you've ever changed your USB jumpers, double check them!
=> If you've never touched the USB jumpers, this issue probably doesn't apply to you
=>
A USB tech reference for geeks
About AC Adapters...
Plug in any AC adapters
=> If your USB hub or device has an AC adapter, plug it in!
=> Don’t believe its power supply is OK simply because you see its power light turn on when connected!
How to view USB Hub and Device Power Usage
Check each USB hub to see if it's bus- or self- powered and check the power usage required by each attached device
Example
For this example, I set-up the following hardware
- I am working on laptop
- The laptop is connected to a docking station which has 3 USB ports. They connect to
- An external USB hard drive
- An external USB CD/DVD drive
- An external USB hub (with its own AC adapter). The hub connects to
- A USB printer
- A USB SanDisk U3 Flash Drive
- A USB antennae for wireless mouse and keyboard
- A USB Audio device
Click thumbnails for full images
![[IMG]](http://img521.imageshack.us/img521/294/hubproperties.th.jpg)