USB Complete fourth- P49

USB Complete fourth- P49:This book focuses on Windows programming for PCs, but other computersand operating systems also have USB support, including Linux and AppleComputer’s Macintosh. Some real-time kernels also support USB.
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USB Complete fourth- P49Chapter 19 Two USB-IF standards for this type of interface are the Inter-Chip USB Supple- ment for low and full speeds and the High-Speed Inter-Chip USB Electrical Spec- ification for high speed. For both interface types, all of the following are true: • The distance between the host and peripheral is 10 cm or less. • The host doesn’t allow peripheral attachment or removal while the inter-chip supply voltage is present. • The interface can use a vendor-specific cable or on-board connection (cir- cuit-board traces). An interface that complies with the Inter-Chip USB Supplement must meet these requirements: • The host always supports full speed and supports low speed if the host com- municates with a low-speed peripheral. The peripheral may support low or full speed. • The interface supports one or more of six defined supply-voltage classes with nominal voltages in the range 1–3V. The low/full speed interface draws no bus current when idle. To save additional power, hardware can switch out the bus pull-up and pull-down resistors during traffic signaling. The High-Speed Inter-Chip USB Electrical Specification defines an interface that uses a high-speed inter-chip (HSIC) synchronous serial interface. The interface uses 240-MHz double data rate (DDR) signaling, which transfers data on both the rising and falling clock edges. A 240-Mhz clock thus supports a 480-Mbps bit rate. An interface that complies with the High-Speed Inter-Chip USB Electrical Specification must meet these requirements: • The host and peripheral support high speed. • The interface uses 1.2V LVCMOS voltages. The HSIC interface consumes power only when a transfer is in progress.75$ To support SuperSpeed, USB 3.0 adds transmitters and receivers and modifies the cables and connectors to carry the SuperSpeed signals.456 The Electrical and Mechanical Interface6TCPUOKVVGTU CPF 4GEGKXGTU For SuperSpeed, each direction has a dedicated pair of wires with a differential transmitter at one end and a differential receiver at the opposite end. The hard- ware interface is based on the PCI Express (PCIe) Gen 2 interface used in expansion buses in PCs. In a PC, the bus uses multiple lanes to transfer multi- ple bits in the same direction at once. SuperSpeed uses a single lane with one signal pair for each direction. A SuperSpeed transmitter must contain a circuit that detects an attached receiver’s load of 18–30Ω. An RC charging circuit can perform this function. Because the SuperSpeed wires carry data at a single speed, an upstream hub that detects a SuperSpeed device knows the device’s speed.%CDNGU USB 3.0 cables can carry both USB 2.0 and SuperSpeed traffic. The cables have additional wires and connector contacts to support SuperSpeed. %QORCVKDKNKV[ USB 3.0 cables and connectors are backwards compatible with USB 2.0. Plugs on USB 2.0 cables fit USB 3.0 receptacles. A USB 2.0 cable attached to a USB 3.0 host or hub can carry low-, full-, and high-speed data. A USB 3.0 Standard-A plug fits a USB 2.0 Standard-A receptacle. Thus you can use a USB 3.0 cable to attach a USB 3.0 device to a USB 2.0 host or hub and communicate at a USB 2.0 speed. Attaching a USB 2.0 device to a USB 3.0 host or hub requires a USB 2.0 cable. USB 3.0 Standard-B and USB 3.0 Micro-B plugs don’t fit USB 2.0 receptacles. To use SuperSpeed, all cables and receptacles in the links between the device and host must be USB 3.0. %QPFWEVQTU A USB 3.0 cable has ten wires (Table 19-5), which include USB 2.0’s power, ground, and unshielded pair plus two shielded pairs with drain wires for Super- Speed. The SuperSpeed interface is dual simplex: each direction has its own pair of wires, each pair has its own ground, or drain, wire, and data can travel in both directions at once. (Full duplex is also bidirectional but uses a single, com- mon ground wire.) The SuperSpeed wires can be shielded twisted pairs or twi- naxial cable (twinax). Twinax is similar to coax but has two inner conductors 457Chapter 19Table 19-5: A USB 3.0 cable has additional wires to support SuperSpeed 9KTG 0COG CV 7UG %QNQT %QPPGEVQT 1 PWR VBUS power Red 2 UTP_D- Unshielded differential pair, negative (USB 2.0) White 3 UTP_D+ Unshielded twisted pair, positive (USB 2.0) Green 4 GND_PWRrt Ground for power return Black 5 SDP1- Shielded differential pair,1, negative (SuperSpeed) Blue 6 SDP1+ Shielded differential pair 1, positive (SuperSpeed) Yellow 7 SDP1_Drain Drain wire for SDP1. – 8 SDP2- Shielded differential pair 2, negative (SuperSpeed) Purple 9 SDP2+ Shielded differential pair 2, positive (SuperSpeed) Orange 10 SDP2_Drain Drain wire for SDP2. Connects to pin 7 on the – connectors. Braid Shield External braid terminated onto metal shell of plug – instead of one. The characteristic impedance of shielded twisted pairs should be 90 Ω. USB 3.0 doesn’t specify wire gauges but provides electrical data for typical val- ues (26–34 AWG) and recommends using the smallest-diameter gauges that meet the ele ...