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USB 2.0 - Hi-Speed USB - FAQ(转发) |
| 作者：yu0714 栏目：通信技术 |
USB 2.0 - Hi-Speed USB - FAQ What is USB 2.0? Add Your Notes Finalized in 2001, USB 2.0 is a complete overhaul to the Universal Serial Bus input/output bus protocol which allows much higher speeds than the older USB 1.1 STANDARD did. USB 1.1 allowed a maximum transfer rate of 12Mbits/second. That rate is now called 'USB.' Though some MANUFACTURERs label their products Full-Speed USB. Note that this seems a bit deceptive. It�s easy to mistake Full-Speed for Hi-Speed. You won't be fooled from now on as you now aware that Full Speed USB is ONLY 12Mbits/second where Hi-Speed USB mode is capable of a much FASTer 480Mbits/second. As an aside, USB mice and keyboards need ONLY 1.5Mbits/s to function. That performance level is also NAMEd 'USB' by the USB Promoter GROUP. To sum it up, USB 2.0 specification incorporates three speeds: Hi-Speed, Full-Speed and Low-Speed. You as a consumer don't need to figure out all the jargons. Just KEEP in mind that ONLY 'Hi-Speed USB' and 'USB' host and DEVICEs exist. How do I know if my PC has USB 2.0? Add Your Notes You can identify whether your PC has Hi-Speed or not relatively easy. Open DEVICE Manager and expand the Universal Serial Bus section. There should be an "Enhanced" USB host controller present. Windows 98 SYSTEMs may use a different NAME, because Hi-Speed USB drivers in these operating SYSTEMs are not provided directly from Microsoft (Windows ME, 2000 and XP get their drivers through Windows Update). These drivers are provided by the MANUFACTURER, and may carry the maker?s NAME (i.e. ADS, Belkin, IOGear, Siig, etc.). There should also be two ?STANDARD? version USB host controllers present as well. They are embedded in the USB chip which routes the differing USB speeds accordingly without user intervention. There are currently 6 MANUFACTURERs of the Hi-Speed USB host SILICON themselves: ALi (Acer Labs) INTEL NEC SiS VIA NVIDIA (shows as "STANDARD" controller Any other brand NAME that appears in DEVICE Manager would likely be an add-in Hi-Speed USB PCI card. The makers above do not make add-in cards, but they do make the chips that are used in them. How do troubleshoot "UNKNOWN DEVICE" error listed in DEVICE Manager? Add Your Notes I wish that there was a simple, SINGLE answer for this. There's ONLY one thing more distressing - no DEVICE recognition at all. Here are the most likely culprits: The USB DEVICE or the USB adapter requires it's own POWER source. If your USB DEVICE or adapter came with an AC POWER "brick", try connecting it. Here's a likely one - the front USB ports on your PC case may be misconnected. I've seen them that way from the factory. It's a GOOD idea to check the connections against specifications. The STANDARD order of connection is Red, WHITE, GREEN, Black. No more than 4 wires per USB bank are needed. Defective DEVICE. Do not assume that all PC components work correctly out of the box. I've seen many new USB DEVICEs that do not work. If you can, try the DEVICE on another PC. All drivers are not installed. Some DEVICEs will require installing the driver PACKAGE before plugging in the DEVICE. Some DEVICEs will also require basic USB files from the Windows CD before the unit will function. The general rule is to always follow installation directions precisely and to have the Windows CD ready. I will now discuss how to address an UNKNOWN DEVICE problem which is caused by a driver deficiency. Try to update the UNKNOWN DEVICE driver from within DEVICE Manager. First try letting Windows search for one. If that fails, go BACK and choose "SELECT from a list" and then "Have disk". Browse to the DEVICE CD and look for the appropriate Windows folder there. Try browsing to the Windows CD (Win9x folder or i386 folder). Lastly, try updated drivers from the MANUFACTURER's web site. Try uninstalling the UNKNOWN DEVICE, unplugging the DEVICE and rebooting. Replug when BACK in Windows. Be certain that you have the correct drivers! You may have gotten the wrong CD or a CD with drivers for more than one DEVICE on it. Cleaning up in Safe Mode may be necessary. Unplug all USB DEVICEs. Reboot the PC. To enter Safe Mode, press the F8 key repeatedly while restarting the PC. Timing is important. Try to press quickly before the Windows LOGO screen appears. Pressing and holding the CTRL key may work too. Choose Safe Mode and open DEVICE Manager. In Windows 2000 and XP, click View > Show hidden DEVICEs. Now locate all USB DEVICEs, HID (Human Interface DEVICEs), USB drives and controllers/hubs. Remove all and save the USB Host Controllers for last. When done, restart and replug USB DEVICEs one at a time. Just remember that you are entitled to SUPPORT from the DEVICE maker. If you can't get help, do not hesitate to return the DEVICE. Some MANUFACTURERs ONLY seem to respond to lost business. It's a shame, but it's true. Send them a message - that you won't accept shoddy GOODs or lackluster SUPPORT. By William DeVercelly How FAST is USB 2.0? Add Your Notes USB 2.0 has a raw data rate at 480Mbps, and it is rated 40 times FASTer than its predecessor interface, USB 1.1, which tops at 12Mbps. Originally, USB 2.0 was intended to go ONLY as FAST as 240Mbps, but then, USB 2.0 Promoter GROUP increased the speed to 480Mbps in October 1999. How will consumers benefit from USB 2.0? Add Your Notes With speed 40 times more than that of USB 1.1, USB 2.0 broaden the range of external peripherals that can be used on a COMPUTER. Even with multiple high-speed peripherals connected to a USB 2.0 bus, the SYSTEM will less likely to hit the bandwidth bottleneck. The new specification also inherits the current USB?s Plug and Play and hot-swapping capability as well as providing BACKward compatibility for USB 1.1 HARDWARE, allowing existing user base to upgrade seamlessly. Do USB 2.0 & USB 1.1 HARDWARE work interchangeably? Add Your Notes You may have heard that USB 2.0 is "BACKward-compatible" with USB 1.0/1.1 (Full-Speed USB). While that's true, USB 1.1 is also forward-compatible with USB 2.0. Whenever a SYSTEM has USB 2.0 ports, you'll find the "Enhanced" USB controller in DEVICE Manager, but you will also find two other USB controllers. These two to mantain BACKward compatibility to USB 1.1 DEVICEs. Each USB 2.0 host actually has 3 chips onboard. The USB controller routes signals to the correct controller chip depending on how a DEVICE is recognized. Where a DEVICE is physically plugged in has no bearing on how it is routed. All ports on a USB 2.0 MOTHERBOARD can host any USB DEVICEs at all as LONG as the SYSTEM and DEVICEs are healthy. The vast majority of USB 2.0 DEVICEs will work on older PCs and Macs. None should flat-out fail unless there are other issues with the SYSTEM. Hi-Speed USB DEVICEs will revert to Full-Speed operation when connected this way. Understand that Hi-Speed is at least ten times FASTer than Full-Speed in actual operation, so the speed difference is quite noticeable - unless you have never experienced Hi-Speed, of course. When it comes to USB hub compatibility between USB 2.0 and USB 1.1, here some facts: A POWERed hub is always preferable to unPOWERed. USB hub ports are not as capable or flexible as real PC ports so it's best not to expect the world of them. USB 1.1 (obsolete) hubs will work fine on USB 2.0 ports, but they cannot utilize USB 2.0 capabilities. They will default to slower speeds. Hi-Speed and Full/Low-Speed USB DEVICEs can coexist nicely on USB 2.0 hubs. Connecting such a hub to a USB 2.0 port is recommended. USB 2.0 hubs can be used on older |
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