TAILIEUCHUNG - USB Complete fourth- P24

USB Complete fourth- P24:This book focuses on Windows programming for PCs, but other computers and operating systems also have USB support, including Linux and Apple Computer’s Macintosh. Some real-time kernels also support USB. | Chapter 7 Figure 7-7. To enable two USB hosts to communicate with each other two USB serial interface engines can share a buffer. Each SIE copies received USB data into the shared buffer and the other device retrieves the data from the buffer and sends the data to the other host. because every PC has a USB port some applications might want to use the interface to communicate between PCs. If both PCs have Ethernet ports the cheapest solution is to forget about USB and use Ethernet. Use a crossover cable to connect the PCs directly or connect the PCs via a hub or router. If Ethernet ports aren t an option a USB host-to-host bridge cable can do the job. The cable incorporates two USB device controllers which may reside in a single chip . Each controller represents a USB device. Each device attaches to a different PC and the devices exchange data via a shared buffer Figure 7-7 . When a PC sends data to its attached device the device writes the data to the shared buffer. The other device in the bridge retrieves the data from the buffer and sends it on to its attached PC. Prolific Technology s PL-2501 Hi-Speed USB Host to Host Bridge Controller is a single chip designed for this type of host-to-host application. The chip contains an 8032 microcontroller and two USB SIEs that access a common buffer. Typically the drivers for bridge cables cause each PC to see the other as a network-connected computer. Another way to achieve a network connection via USB is to use USB Ethernet adapters. 206 Device Classes An alternate approach for host-to-host communications is to use two FTDI FT232R USB UARTs and cross-connect the asynchronous interfaces in a null-modem configuration. Each PC then has a COM port that communicates with a COM port on the other PC. The exception to the host-and-device rule is the USB Standard-A to USB Standard-A cable. With host driver support SuperSpeed devices will be able to use this cable to communicate with each other. Chapter 19 has more about .

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