A USB system has an asymmetric design which consists of a host controller and multiple devices connected in a tree-like fashion with the use of special hub devices. 127 devices per host controller can be connected.
These signals are transmitted on a twisted pair of data cables, labeled D+ and D-. These collectively use half-duplex differential signaling to combat the effects of electromagnetic noise on longer lines. D+ and D- operate together and are not separate connections.
USB supports three data rates. The first one is data rate of 1.5 Mbits per second which is used to connect devices like mouse, keyboard etc. The second one has a data rate of 12 Mbits per second and the devices use the entire bandwidth with this connector which operates on first come first serve basis. The third one, called the USB 2.0 has a Hi-Speed rate of 480 Mbit per second. The advantage with USB 2.0 is that it supports low speed USB devices by reducing its bandwidth.
USB
|
Pin |
Name |
Description |
|
1 |
VCC |
+5 VDC |
|
2 |
D- |
Data - |
|
3 |
D+ |
Data + |
|
4 |
GND |
Ground |
