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14 E5805A USB/RS232 Interface
E5805A USB/RS232 Interface
Understanding the E5805A and USB Hubs
Hubs, critical components in the USB architecture, are wiring
concentrators that enable the attachment of multiple devices,
thus converting a single attachment point into multiple
attachment points. USB architecture allows a cascaded multiple
hub configuration with certain power limitations (explained
later in this section). See Figure 1.
Figure 1 Hub Architecture
Each hub has an upstream port, connecting to the host, and
multiple downstream ports, connecting to downstream devices,
possibly including other hubs. A hub can detect attachment and
detachment of downstream devices and enable and monitor the
distribution of the power to downstream devices via their
integral hardware and the operating system.
Each USB device reports its power requirements to the
operating system, which then enables and disables the device as
a function of its power requirements and the amount of
available power. High powered devices typically need to be
connected to a self-powered hub that obtains power from its
external power supply and provides up to 500 mA for each
downstream port. Only low powered devices, such as a mouse,