Книга: Advanced PIC Microcontroller Projects in C

8.1 Speed Identification on the Bus

8.1 Speed Identification on the Bus

At the device end of the bus, a 1.5K pull-up resistor is connected from the D+ or D– line to 3.3V. On a full-speed bus, the resistor is connected from the D+ line to 3.3V, and on a low-speed bus the resistor is from D– line to 3.3V. When no device is plugged in, the host will see both data lines as low. Connecting a device to the bus will pull either the D+ or the D– line to logic high, and the host will know that a device is plugged into the bus. The speed of the device is determined by observing which line is pulled high.

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