The pipe defines the type of data transfer that may occur between that endpoint and the host.ĭata transmissions using USB are termed “transfers”. Pipes are automatically deleted when a device is disconnected. The USB host establishes a logical connection, called a “pipe” to the endpoints on connected devices. The protocol used by USB is essentially master/slave all communication is initiated by the host.

Every device must, as a minimum include Endpoint 0 with both input and output buffers. A device can have up to 16 numbered endpoints, each of which may contain one or two buffers (endpoint addresses), one handling data into the device and the other out. The topology of a USB system is termed a “tiered star”, with a “root hub” in the host which connects to all the USB devices, either directly or via further hubs, thus:Ī USB peripheral controller includes a physical interface to the USB cable connector, of course, but it also incorporates a number of data buffers called “endpoints”. There are broadly three types of device that might support USB: a “host”, which is in control of the bus (like a PC), a “function”, which is a peripheral device, like a mouse, or an “On-The-Go” device that might function as a host or a function at different times, like a digital camera. More recently, USB 3.x has introduced SuperSpeed (5Gb/s) and beyond. USB 2.0 introduced High Speed (480Mb/s), which helped when larger quantities of data were being transferred this applied to larger hard drives and streaming media. In its first versions, USB offered Low Speed (1.5Mb/s) and Full Speed (12Mb/s) these addressed most user requirements. A USB subsystem can support up to 127 devices, so it has no lack of capacity. It minimises the number of connectors and cables and offers a true “plug-n-play” experience. USB was invented to provide an effective and more user-friendly alternative to traditional serial and parallel interfaces. Although an embedded software engineer need not understand every last detail of how USB works, some insight is useful, even if a commercially available USB stack is employed.

The simplicity of its use hides complexity in its implementation. Adding a peripheral device is usually straightforward for even the most non-technical users. There is no doubt that, since the introduction of USB over 20 years ago, personal computers have become easier to use.

Usb 2 vs usb 3 for mice