Datasheet

266
ATmega16U4/32U4 [DATASHEET]
Atmel-7766J-USB-ATmega16U4/32U4-Datasheet_04/2016
 The “Session_valid” signal is active high when the voltage on the UVBUS pad is higher or equal to 1.4V. If
lower than 1.4V, the signal is not active
 The VBUS status bit is set when “Session_valid” signal is active (VBUS > 1.4V)
 The VBUSTI flag is set each time the VBUS state changes
 The USB peripheral cannot attach to the bus while VBUS bit is not set
21.12 USB Software Operating Modes
Depending on the USB operating mode, the software should perform some the following operations:
Power On the USB interface
 Power-On USB pads regulator
 Configure PLL interface
 Enable PLL
 Check PLL lock
 Enable USB interface
 Configure USB interface (USB speed, Endpoints configuration...)
 Wait for USB VBUS information connection
 Attach USB device
Power Off the USB interface
 Detach USB interface
 Disable USB interface
 Disable PLL
 Disable USB pad regulator
Suspending the USB interface
 Clear Suspend Bit
 Freeze USB clock
 Disable PLL
 Be sure to have interrupts enable to exit sleep mode
 Make the MCU enter sleep mode
Resuming the USB interface
 Enable PLL
 Wait PLL lock
 Unfreeze USB clock
 Clear Resume information