| 摘要 |
A universal serial bus (USB) device and a USB system are provided. The USB device comprises an electrical physical layer (EPHY) module, a logical physical layer (LPHY) module and a link layer module. The EPHY module reads the voltages of first and second transmission lines of a USB cable to extract a recovery clock and data. The LPHY module detects the recovery clock and data to output an indication signal. When the recovery clock is not detected, the LPHY module sets the indication signal to a predetermined value. The link layer module determines whether the indication signal is at the predetermined value, and makes a state machine thereof leave a normal operation state when the indication signal has been maintained at the predetermined value over a predetermined time period.
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