Agilent Technologies E5805A - Manual (Page 19)

E5805A USB/RS232 Interface
E5805A USB/RS232 Interface 15
can be connected to a bus- powered hub, which obtains power
from its upstream host and provides up to 100 mA for each
downstream port.
Due to the limited available power for bus- powered hubs,
cascading two bus- powered hubs is an illegal topology, and
devices connected to the second hub will not function. USB
specifications limit the connection of a bus- powered hub to a
self- powered hub or host only.
According to the USB Specification, the maximum limit of hubs
cascaded in series cannot exceed five. In other words, you may
have a maximum of five hubs between any device and the host.
This does not mean that the maximum number of hubs in a
system is five. Indeed, up to seven hubs can be connected
parallel at any given level. You must tally both external and
embedded hubs when counting downstream hubs.
N O T E
The E5805A is a bus-powered device and, therefore, must not be
connected to a bus-powered hub.