OVERVIEW

The Universal Serial Bus was conceived as an easy-to-use desktop expansion bus, and it is serving this role very well. But, as with all good technological solutions, creative engineers throughout the world are extending the applications envelope of USB. Advances in storage technologies, and the increase in speed offered by USB 2.0, further fuel the dynamic range of USB solutions.

The original model of a USB I/O device was one that was easy to connect to a PC host. Once this connection was made, the device stayed connected and served as a semipermanent resource to the PC host. Printers, scanners, keyboards, and mice are good examples of this resource usage model. The hot-plug capability of USB allowed these resources to be reallocated, and this generally improved the usefulness of a USB-based I/O device.

This chapter looks at the growing range of portable and handheld USB-based I/O devices. I shall use the term casually connected to contrast these applications from their semipermanent resource brethren. Most portable and handheld devices function without a permanent connection with the PC host; when they are connected, additional capability is available. We shall look inside a variety of products, and I hope to expand your ideas about what can be done, to enable you to create additional unique designs. I will present a variety of solutions, with a focus upon the building-block nature of each design, and will then direct you to a variety of additional resources that will enable you to start with...