about USB – Universal Serial Bus Controller
Universal Serial Bus (USB):
USB is a standard for serial bus used for interfacing devices to the host computer. Core group companies like the Intel, IBM, Compaq, Microsoft etc. together united created the USB standard. The first specification on USB was released in 1996. The first computer with USB ports offering “legacy” ports was the original Apple iMac G3, introduced in May 6 of 1998. The problems which are faced by the earlier versions were put off by the version USB 1.1 which was introduced in 1998.
USB version history :
USB is classified into three different versions namely the USB 1.0, USB 2.0, USB 3.0 which was introduced in January 1996, September 1998 and September 2007 respectively. The range of speed varies between the different versions. The USB 1.0 version has the lowest data rate range from 5 Mbits/s and 12 Mbits/s. The USB 2.0 version has a data rate of about 480 Mbits/s. Third version has the maximum transfer rate of about 5.0 Gbits/s.
USB Signaling:
USB signals are normally transmitted over a twisted pair cable having 90ohms of impedance. Half duplex signaling is normally used to overcome the disturbances caused by the electromagnetic waves. The signals which are transmitted are 0.0-0.3 volts at the lower level and at the higher level it ranges from 2.8-3.6 volts for full and low speeds and for high speeds the signal level range at the lower level is -10-10 mV and for higher level is 360-440 mV. The cable wires are not removed in the full speed mode while 45 ohms are grounded in the high speed mode.
The new versions of USB avail high speed but are expected to control commercial markets in 2009 this year..