USB disconnect/reconnect | Cypress Semiconductor
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How can a device detect a USB disconnect/reconnect ?
In order to detect a device disconnect the device will have to be self powered.The method used to detect if a device is connected to the bus is to monitor the VBUS signal. Connect the VBUS to an external I/o pin configured as an input.Make sure you have pull down resistors (of high resistance to maintain the suspend current of 100 mA) on VBUS. Please refer to the appnote "
Monitoring the EZ-USB FX2LP™ VBUS" for more information.