USB host pull-up drop-down resistor

About the USB pull-up resistor, not just a random resistance to any resistor on the OK.

When your USB is the main device , the d+, D-on is connected to a 15K pull-down resistor, which allows the d+, D-to remain low when no device is plugged in;

When interfacing to slave devices , the different transfer rates can be set by the pull-up resistor, when the d+ is connected to a 1.5K pull-up resistor, it can work in high-speed mode such as 12MBPs, when the D-to-1.5K pull-up resistor works in a low-rate mode such as 1.5MPBs.

The main USB automatic recognition from the device for high speed or low speed on the pull-up resistor in the d+ or D-difference, the resistance of the non-standard will affect the USB automatic identification allocation of resources, there can not be found hardware or use to the general hardware discovery failure, etc., so do not casually pull the resistor, the first standard USB hardware interface circuit.

USB host pull-up drop-down resistor