USB transfer modes
Univeral serial bus supports Control, Interrupt, Bulk and Isochronous transfer modes.USB transfer rates: Low Speed, Full Speed, Hi-speed.
USB supports three data rates: Low Speed (1.5 Mbit per second) that is mostly used for Human Input Devices (HID) such as keyboards, mice, joysticks and often the buttons on higher speed
devices such as printers or scanners; Full Speed (12 Mbit per second) which is widely supported by USB hubs, assumes that devices divide the USB bandwidth between them in a first-come first-serve
basis - it"s easy to run out of bandwidth with several devices; Hi-Speed (480 Mbit per second) was added in USB 2.0 specification. Not all USB 2.0 devices are Hi-Speed. A USB device must indicate
its speed by pulling either the D+ or D- line high to 3.3 volts. These pull up resistors at the device end will also be used by the host or hub to detect the presence of a device connected to its port.
Without a pull up resistor, USB assumes there is nothing connected to the bus. In order to help user to identify maximum speed of device, USB device often specify it's speed on it's
cover with one of USB special marketing logos.
Jac Londe on 23 Apr 12delta ray, in physics, any atomic electron that has acquired sufficient energy by recoiling from a charged particle passing through matter to force, in turn, some dozens of electrons out of other atoms along its own trajectory. The charged particle giving rise to delta rays generally is relatively large, such as an alpha particle (composed of two protons and two neutrons), but may also be a high-speed electron. This particle, as it slows down in matter, forces thousands of electrons out of atoms by ionization, producing a wake of electrons and positive ions (electron-deficient atoms) that can be detected. The detached electrons are usually of such low energy that they cannot produce further ionization. But periodically, a relatively large amount of energy is transferred to an electron by a nearly head-on collision along the path of the primary ionizing particle. These are the energetic electrons that cause secondary ionization and are referred to as delta rays. On a developed photographic emulsion, in which strongly ionizing particles have left dense tracks, delta rays appear as thin wavy spurs or branches. The term delta ray, first used by the British physicist J.J. Thomson, is sometimes extended to any recoil particle that causes secondary ionization. LINKS Related Articles
