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2 Camera Basics
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2.9 USB Interface
History and development
Structure and topology
USB 2.0 cabling and connection
USB 3.0 cabling
Data transmission and bandwidth
2.9.1 History and Development
The Universal Serial Bus (USB) is an interface which enables you to easily connect various devices to a PC. As
all data exchange is controlled by the PC, no additional interface controller is needed. Further advantages of USB
are:
The PC does not have to be shut down when connecting USB devices (hot plugging).
USB devices can be supplied with power from the PC.
High bandwidth for data transmission.
The USB standard was developed by a group of companies including Compaq, IBM, Intel, and Microsoft. Version
1.0 was presented in 1995. The slightly faster USB 1.1 standard followed in 1998.
At first, the USB interface was designed to connect peripheral devices such as printers, mice, or keyboards. With
the introduction of USB 2.0 in 2000, the transfer rate increased to 480 Mbit/s, making USB 2.0 suitable for
connecting devices with higher data volumes (such as mass storage devices, scanners, or cameras).
In 2008, with USB 3.0 a new version of the interface has been published, which is significantly faster than USB 2.0
(400 MByte/s).
2.9.2 Structure and Topology
USB uses a tree topology and is host-controlled. That means that a PC with host functionality is mandatory for
using USB. Therefore, it is not possible to directly connect two USB devices (with the exception of USB on-the-go
compliant devices). Neither is it possible to connect a camera to a PDA device.
Theoretically, 127 devices can be connected to a host controller. Using external hubs or repeaters, even more
devices can be connected, and from a greater distance. Provided that a maximum of 5 hubs/repeaters may be
daisy-chained, USB devices can be connected in up to seven levels.
Note
The maximum bandwidth of 480 Mbit/s per USB 2.0 host or 400 MByte/s per USB 3.0 host cannot be exceeded.
Therefore, the maximum possible frame rate will be reduced if image data from multiple USB cameras is
transferred simultaneously.
The available bandwidth might also be decreased when you use hubs or repeaters. You can reduce the bandwidth
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