| 摘要 |
PROBLEM TO BE SOLVED: To provide a USB communication device, capable of optionally switching a communication speed mode by USB depending on prioritization to communication speed or prioritization to communication quality. SOLUTION: A USB host controller 1b selects EHCI 1a1, and performs connection with a USB device controller 2a in high-speed mode to perform high-speed communication. When the communication quality is deteriorated by noise in the high-speed communication by high-speed mode, and USB device control firmware 2b counts communication failure time for a fixed time or more, the USB host controller 1b selects OHCI/UHCI 1a2 and performs switching to a full-speed mode to reduce the communication speed. According to this, the communication quality between a USB host 1 and a USB device 2 is stabilized. Since transfer data is not omitted at the time of switching from the high-speed mode to the high-speed model, the communication at the time of switching is stable. COPYRIGHT: (C)2007,JPO&INPIT
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