Abstract
This chapter describes the basic principles of the Universal Serial Bus (USB) and shows how to use USB-based applications with PIC microcontrollers. The USB is a high-speed serial interface that can also provide power to devices connected to it. A USB bus supports up to 127 devices connected through a four-wire serial cable of up to three or even five meters in length. USB is a host-centric connectivity system where the host dictates the use of the USB bus. Each device on the bus is assigned a unique USB address, and no slave device can assert a signal on the bus until the host asks for it. When a new USB device is plugged into a bus, the USB host uses address 0 to ask basic information from the device. Then the host assigns it a unique USB address. Data is transmitted on a USB bus in packets. A packet starts with a sync pattern to allow the receiver clock to synchronize with the data. The data bytes of the packet follow, ending with an end of packet signal. Some of the PIC18 microcontrollers support USB interface directly, such as the PIC18F4550 microcontroller contains a full-speed and low-speed compatible USB interface that allows communication between a host PC and the microcontroller.
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