[Country EMBED strategy] [161] [Introduction to USB bus]

USB History

USB (Universal serial Bus), Universal Serial bus, is an external bus standard. Used to standardize the connection and communication between a computer and an external device. USB was introduced at the end of 1994 by companies such as Intel, Compaq, IBM, Microsoft, and more. Since the 1996 heap, has successfully replaced the serial port and the port. Become one of the essential interfaces of today's personal computers and a large number of smart devices.

USB1.0 appeared in 1996 at a speed of only 1.5Mbps. The 1998 upgrade to USB1.1, the speed has also increased to 12Mbps, called full speeds.

The USB2.0 specification evolved from the USB1.1 specification. It has a transmission rate of 480Mbps, called High speed.

The USB3.0 offers 10 times times the transmission speed of USB2.0 and higher energy efficiency, known as super speeds.

USB Hardware Interface

1. Standard a port

2. Standard B Port

3.mini-usb

4.micro-usb

USB Signal Cable

The USB port has 4 wires. Two power cords, two signal cables. The output voltage and current of the USB interface is 500mA. When the data cable d+ and D-the voltage difference is greater than 200mV is the output is 1, the voltage difference is less than 200mV output of 0.

USB power cord: marked with vcc,power,5v or 5VSB

USB Data Cable (positive): marked with data+,usbd+,pd+ or usbdt+

USB Data Cable (negative): marked with data-,usbd-,pd-or usbdt-

USB ground: Marked with GND or ground

System topology

Hosts (host controllers), Root hubs (hubs), and external devices make up a USB system.

The common master controller specifications are:

OHCI: The main non-PC system on the USB chip, is generally the USB1.1 standard.

UHCI: mainly USB controller chips on Intel and via motherboards. is generally the USB1.1 standard.

EHCI: It is developed by several vendors such as Intel, and is compatible with OHCI and UHCI. is generally the USB2.0 standard.

[Country EMBED strategy] [161] [Introduction to USB bus]