19
CHAPTER 3: Installation
3.4 Power Controls
When the hub is connected to the USB connection,
it initially draws less than 1⁄10of an amp from the host
connection. Each port is enabled one at a time. Initially,
all attached devices are only allowed to draw 1⁄10amp or
less each.
When the hub is identified, it tells the host whether it is
bus-powered or self-powered. If the hub is bus-powered,
the device driver should only allow low-power devices to
be enabled. If the hub is self-powered, the device driver
can allow low-power and/or high-power devices to be
attached.
NOTE
Early device drivers may not enforce these power
limits. However, the USB Director/4-Port Hub is
designed to automatically protect the host connection
and the hub itself from overcurrent conditions if they
exist.