The data pipe uses a combination of the address, endpoint and also the direction to define it. The host then uses the concept of a data pipe to ensure the data to and from a device is correctly directed or the source is known. Because pipes correspond to endpoints, the terms are sometimes used interchangeably. In reality, a USB data pipe is a connection from the host controller to a logical entity within a device, i.e. These can be considered as being logical channels within the data flow on the bus. The communication within USB is based around the concept of using data pipes. The zero endpoints are used for a variety of activities including auto-detection and configuration of the device on the bus and the two zero endpoints are the only ones accessible until the device is properly connected on the bus. Although each device can have sixteen input and sixteen output endpoints, it is very rare for them all to be used. input or output, but not both, and devices can have up to 16, of which one each for the input and output must be reserved as the 'Zero Endpoint' for that direction. These are the actual sources and destinations for communications between the host and the device.Įndpoints can only operate in one direction, i.e. In addition to the address, the device also contains endpoints. To achieve this, when a device is attached to the bus it is assigned a unique number or address by the host for the time it is connected. With data for all devices beings ent along the bus, it is necessary for the USB operation that the data is only accepted by the required function. Typical physical arrangement for a USB network Selecting USB function destination In terms of the data flow, the signals travel along the bus so that it is accessibly by all the functions, but only the destination function accepts it. The actual physical layout of the USB system will vary according to the actual situation, but the operation is always basically the same. The physical layout of a USB 'network' may consist of the host with two (for example) ports and each of these may have a hub attached, to which further devices or 'functions' are attached. Mice, keyboards, Flash memories, etc, etc.ĭevice: This term is collectively used for hubs and functions. It can be on a host, or a hub.įunction: These are the peripherals or items to which the USB link is connected. Port: This is the socket through which access to the USB network is gained. It is possible to plug one hub into another to expand the capability and connectivity further. Hub: The hub is a device that effectively expands the number of ports available - it will have one connection to the upstream connection, and several downstream. The host has a hub contained within it and this is called the Root Hub. Host: The host is the computer or item that acts as the main element or controller for the USB system. In terms of the definitions of the entities in a USB network, there are three main elements: In order to understand how the data transfers and the protocol operates within the USB environment, it is first necessary to understand how USB is physically set up and how it appears to the system / host.įor most systems using USB, the host will be some form of computer: desktop, laptop, tablet, etc, although this does not always need to be the case.Īlthough there is a lot of variation in the way a USB system may appear to be set up, essentially the same structure will be used and this reflects in the way it operates. The bus also operates in a particular way, seeing the various devices attached to it independently of the actual physical layout of the system.Īlthough some changes have been made between the different updates to the USB standard as it progressed from USB 1 to USB 2, USB 3, and USB 4, the basic operation, protocol, signalling and data transfer modes, data packet format, etc are basically the same. To achieve this the system has a defined the USB data transfer protocol, data packet format, etc that enables the data to be formatted and carried in a defined way that provides the reliable communication. Selection of USB connectors, adapters and cables Whether USB 1, USB 2, USB 3 or even USB 4, the data requires a standardised method of transfer over the USB interface along with a standard format for the USB data packets. USB, Universal Serial Bus is very easy to use providing a reliable and effective means of transferring data and it is used in many areas from small memory sticks, to external hard drives, printers and many more peripherals. USB introduction USB standards Connectors, pinouts & cables Data transfer & protocol USB 3 USB-C USB hubs How to buy best USB hub USB Operation: Protocol, Data Transfer & Packets USB, Universal Serial Bus has a defined protocol for the data transfer using a variety of specific types of data packets for its operation.
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