Usb Basics; History And Development; Structure And Topology - IDS uEye series User Manual

User Manual uEye Cameras V3.32
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USB Basics

4.1

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 Mbps,
making USB 2.0 suitable for connecting devices with higher data volumes (such as mass storage
devices, scanners, or cameras).
4.2

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.
Figure 9: USB Topology
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The maximum bandwidth of 480 Mbps per USB 2.0 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 required for each camera by lowering the frame rate or the
image size.
© 2009 IDS Imaging Development Systems GmbH