LaCie manual LaCie SAFE Hard Drive, User Manual, page, Troubleshooting, Important Info

LaCie SAFE Hard Drive	Troubleshooting
User Manual	page 38

Technical note: Technically, you can connect up to 127 devices to a single USB bus. For more than two devices, you must make new connections using a peripheral called a "hub." A hub, which you hook up directly to a USB connector on your computer, usually has 4 or 7 output connections enabling you to connect the same number of peripherals. One of the hub's main functions is to regenerate signals that lose part of their strength as they are transmitted via the USB cable. By connecting yet another hub to a connector on the existing hub, you can then plug in a new set of peripherals and so on, up to a maximum of 127.

You can use your USB 2.0 devices with USB

1.1hubs, but the peripherals will be limited to USB 1.1 performance levels. As USB 2.0 is backwards compatible, you will be able to con- nect USB 1.1 devices to USB 2.0 hubs; howev- er, the USB 1.1 devices will still maintain their

normal performance levels (i.e. 12 Mb/s).

In practice, users who desire enhanced USB 2.0 throughput will need to connect their USB 2.0 hardware on both ends of a 2.0 hub to achieve the "high-speed" mode. On one end, a USB 2.0 compliant host controller resides on the host PC to manage the enumeration pro- cess and power management. On the other end, USB 2.0 hardware must be connected directly to the root hub or through a USB 2.0 hub.

Some hubs have no power supply and others are self-powered. When you choose a hub, opt for the self-powered variety, as they have their own AC adapter. The most powerful hubs pro- vide 0.5A of power to each port. If you buy a hub, make sure that it supports per-port switch- ing. This function prevents the entire chain of peripherals from freezing up if one of them is not working properly or is down.

Important Info:

•Avoid using USB connectors found on cer- tain peripherals such as keyboards. These are passive (or pass-through) connectors that lead to power loss and unstable operation.

•Only use USB cables shorter than 5 meters (approximately 15 feet). Using longer cables cause the peripherals to malfunction due to excessive reduction in electrical signal strength.