LaCie Mobile Drive User Manual - page 25
LaCie Mobile Drive User’s Guide 04/17/2003 v.2
25
low-speed on a USB 2.0 bus. Even though USB 1.1 devices won’t run any faster, they
can work alongside USB 2.0 devices on the same bus. However, if you plug in a USB
2.0 device to a USB 1.1 bus, the speed of the USB 2.0 device will decrease to
12Mb/s.
What is a USB hub? Will USB 2.0 devices work on USB 1.1 hubs and
vice versa?
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 1.1 hubs, but the peripherals will be
limited to USB 1.1 performance levels. In the near future, USB 2.0 repeaters will be
available, able to communicate in three modes: high-speed (480Mb/s), full-speed
(12Mb/s), and low-speed (1.5Mb/s). As USB 2.0 is backwards compatible, you will
be able to connect USB 1.1 devices to USB 2.0 hubs; however, 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 process 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 provide 0.5A of power to each port.
If you buy a hub, make sure that it supports per-port switching. This function prevents
the entire chain of peripherals from freezing up if one of them is not working properly
or is down.
Important Note
: Avoid using USB connectors found on certain
peripherals such as keyboards. These are passive (or pass-through)
connectors that lead to power loss and unstable operation.
Important Note:
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.
You will find additional information at the following Internet address:
http://
www.lacie.com/usb