4.1.1 Bus Topology Due to timing constraints allowed
for hub and cable propagation times, the maximum number of tiers
allowed is seven (including the root tier).
layers (including the root layer).
Only functions can be enabled in tier seven
.
4.1.1.1 USB Host
There is only one host in any USB system.
4.1.1.2 USB Devices
USB devices are one of the following:
Hubs, which provide additional attachment points to the USB
Functions
, which provide capabilities to the system, such as an ISDN connection, a digital joystick, or
speakers
USB devices present a standard USB interface in terms of the following:
4.2 Physical Interface
4.2.1 Electrical
There are three data rates:
The USB high-speed signaling bit rate is 480 Mb/s.
The USB full-speed signaling bit rate is 12 Mb/s.
A limited capability low-speed signaling mode is also defined at 1.5 Mb/s.
4.2.2 Mechanical
4.3 Power
4.3.1 Power Distribution
4.3.2 Power Management
4.4 Bus Protocol
The USB is a polled bus. Poll the bus.
The Host Controller initiates all data transfers
.
Most bus transactions involve the transmission of up to three packets
.
4.5 Robustness
4.5.1 Error Detection
4.5.2 Error Handling
4.6 System Configuration
4.6.1 Attachment of USB Devices
4.6.2 Removal of USB Devices
4.6.3 Bus Enumeration
Bus enumeration is the activity that identifies and assigns unique addresses to devices attached to a bus.
Bus enumeration is the activity of identifying and assigning unique addresses to devices connected to a bus.
Because the USB allows USB devices to attach to or detach from the USB at any time, bus enumeration is an
on-going activity for the USB System Software.
Ongoing activity of the software.
Additionally, bus enumeration for the USB also includes the detection and processing of removals
.
for hub and cable propagation times, the maximum number of tiers
allowed is seven (including the root tier).
layers (including the root layer).
Only functions can be enabled in tier seven
.
4.1.1.1 USB Host
There is only one host in any USB system.
4.1.1.2 USB Devices
USB devices are one of the following:
Hubs, which provide additional attachment points to the USB
Functions
, which provide capabilities to the system, such as an ISDN connection, a digital joystick, or
speakers
USB devices present a standard USB interface in terms of the following:
4.2 Physical Interface
4.2.1 Electrical
There are three data rates:
The USB high-speed signaling bit rate is 480 Mb/s.
The USB full-speed signaling bit rate is 12 Mb/s.
A limited capability low-speed signaling mode is also defined at 1.5 Mb/s.
4.2.2 Mechanical
4.3 Power
4.3.1 Power Distribution
4.3.2 Power Management
4.4 Bus Protocol
The USB is a polled bus. Poll the bus.
The Host Controller initiates all data transfers
.
Most bus transactions involve the transmission of up to three packets
.
4.5 Robustness
4.5.1 Error Detection
4.5.2 Error Handling
4.6 System Configuration
4.6.1 Attachment of USB Devices
4.6.2 Removal of USB Devices
4.6.3 Bus Enumeration
Bus enumeration is the activity that identifies and assigns unique addresses to devices attached to a bus.
Bus enumeration is the activity of identifying and assigning unique addresses to devices connected to a bus.
Because the USB allows USB devices to attach to or detach from the USB at any time, bus enumeration is an
on-going activity for the USB System Software.
Ongoing activity of the software.
Additionally, bus enumeration for the USB also includes the detection and processing of removals
.