Method of emulating an attachment and detachment of a USB device

摘要

A pull-up resistor is connected to a VUSB pin of a USB device and either the D+ line or the D- line of a USB cable plugged into a port. The VUSB pin is disconnected from a voltage source under software control to float the pull-up resistor from the D+ line or the D- line such that there is no current flow through the pull-up resistor, the D+ line or the D- line. Because there is no current flow through the D+ line or the D- line, the host determines that the USB cable has been unplugged from the port and the USB device detached even though the USB cable remains physically plugged into the port. Under software control, the voltage source is connected to the VUSB pin, whereupon the host determines that a device has been connected and will start the enumeration process.