Digi 1 manual Understanding Hubs, Example of a Typical Hub Configuration

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Understanding 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.

PC

Host

Hubport

Edgeport

Edgeport

Hubport

 

 

Edgeport

bu s-powered hub

scanner

joystick mouse

Figure 1: Example of a Typical Hub Configuration

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, such as the Hubport, which 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, 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. Since Edgeport/421, Edgeport/42, Edgeport/42+, and Edgeport/416 operate as self-powered hubs, they are not affected by this limitation.

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.

Edgeport Installation Guide (90000403 Rev. G) – Page 17

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Contents Edgeport Table of Contents Edgeport Products Edgeport/8r RJ-45 Pin Assignments Cabling EdgeportEdgeport/8rr RJ-12 Pin Assignments Using the Printer Port Installing the Hub DriversEdgeport/21 Edgeport/42, Edgeport/421 Edgeport/416 Edgeport/2c Edgeport/21c, Edgeport/22c Installing the Printer PortFor Windows 98, CE, SE, Me, 2000, and XP Users For Windows NT Edgeport Driver InstallationFor Windows XP, 2000, and 2003 Server For Windows 98, and MeEdgeport Installation Guide 90000403 Rev. G For All Edgeports except the Edgeport/1 System Status LightFor all Edgeport Products except Edgeport/416 Mounting DiagramsFor All Windows Operating Systems Edgeport Utility ProgramGeneral Tab Edgeport Installation Guide 90000403 Rev. G Fast Reads Edgeport Installation Guide 90000403 Rev. G Version Tab Advanced Tab Understanding Hubs Example of a Typical Hub ConfigurationFCC Regulation Part 15 Declaration of Conformity DoC Regulatory & Other InformationFor U.S. Government use For non-U.S. Government useEMC European Community CE Mark Declaration of Conformity DOCEN55022 UL/CSA Safety InformationEuropean Contact Digi International