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Accomplishing USB Electrical Disconnection with a Microcontroller without Additional External Hardware Disclosure Number: IPCOM000014115D
Original Publication Date: 2000-Mar-01
Included in the Prior Art Database: 2003-Jun-19

Publishing Venue



A firmware algorithm is disclosed which accomplishes electrical disconnection from the industry standard Universal Serial Bus (USB) for a microcontroller which does not have the capability to disable bus resets after USB communications has been established. This approach enables the device to stay disconnected from the USB bus long enough for a USB hub to recognize the device disconnection. No additional circuitry is required using this approach. The following algorithm is implemented: a memory pattern is written which signals 'disconnect on reset' after the USB device has been configured to initiate disconnection with the USB bus, the device enables a watchdog timer, disables all interrupts and then executes a dead-end code sequence until the watchdog reset occurs when starting after reset, the microcontroller checks for the 'disconnect on reset' pattern in memory the microcontroller disables bus resets before any USB communications is established the 3.3 volt regulator required to indicate USB bus connection is turned off the microcontroller firmware delays for an amount of time adequate for a USB hub to recognize that the device has been disconnected a 'no disconnect' pattern is written into memory and the microcontroller again resets using the watchdog timer (proceed to step