Hello, micro USB interface detection principle is as follows: first USB hub of each downstream port of D +, D -, respectively, connected to a 15K ohm pull-down resistor to GND, so that in the hub of the port suspension, it is the two pull-down resistor pulled to a low level, and in the USB device side, in the D + or D - on the pull-up resistor connected to the 1.5k ohms, so that for full-speed devices and high-speed devices is connected to the D +, and low-speed devices is connected to the D -, so that when the device is plugged into the hub, there is a 1.5k ohms pull-up resistor. This way for full-speed and high-speed devices, the pull-up resistor is connected to D+, while the low-speed device is connected to D-, so that when the device is plugged into the hub, there is a 1.5k pull-up resistor and 15k pull-down resistor dividing the voltage, and as a result, one of the differential data lines is pulled high. After the hub detects this state, it will report to the USB master controller (or to the USB master control through his upper layer of the hub), so that the insertion of the device is detected. USB high-speed device is first recognized as a full-speed device, and then through the confirmation between the HOST and the Dvice, and then switched to the high-speed mode, high-speed mode, is the current transfer mode, which will be the pull-up resistor of the D + pull-up resistor is disconnected. Dongguan Taiwei Electronics specializes in precision headphone holders, DC power holders, Type-C, MICRO USB, TFC/SIM CARD, medical connectors, battery holders, shrapnel, key switches and other products. Learn more products into Alibaba.