Datasheet
68
Chapter 1
N
Personal Computer System Components
Be aware of the limitations in the USB specification. The commonly quoted length limit
for USB cables is 5 meters. If you use hubs, you should not use more than 5 hubs between
any two components.
Through the use of a 7-bit identifier, overall, no more than 127 devices, including hubs,
should be connected back to a single USB host controller in the computer, not that you would
ever want to approach this number. The 128th identifier is used for broadcasting. No intercon-
nection of host controllers is allowed with USB; each one and its connected devices are isolated
from other controllers and their devices. As a result, USB ports are not considered networkable
ports. Consult your system’s documentation to find out if your USB ports operate on the same
host controller.
From the perspective of the cable’s plug, Type A is always oriented toward the system
from the component. As a result, you might notice that the USB receptacle on the computer
system that a component cables back to is the same as the receptacle on the USB hub that
components cable back to. The USB hub is simply an extension of the system and becomes
a component that cables back to the system.
FIGURE 1.50 USB cables and connectors
FIGURE 1.51 A USB hub
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