The internal oscillator can be configured to run up to 12 MHz, but the maximum clock frequency that can be achieved depends on the specific configuration and the quality of the external crystal or resonator used. Typically, it can reach up to 10 MHz.
To configure the USB interface to work in device mode, you need to set the USB_MODE register to 0x02, enable the USB clock, and configure the USB pins as outputs. You also need to implement the necessary USB device firmware to handle the USB protocol.
Yes, the ADC can be used in sleep mode, but it requires the ADC clock to be enabled and the ADC to be configured in the sleep mode. The ADC will wake up the microcontroller when a conversion is complete.
To implement a bootloader using the UART interface, you need to configure the UART to receive data, implement a protocol to receive and store the firmware data in flash memory, and then jump to the bootloader code to execute the new firmware.
The minimum voltage required for the microcontroller to operate is 1.8V, but it is recommended to operate at a minimum of 2.0V to ensure reliable operation.