Is the VBUS signal required to be connected on 8-bit USB MCUs?
The USB transceiver on these MCUs has a “USB active” signal. This signal is required for the transceiver to communicate over USB.
On devices prior to the EFM8UB1, the VBUS pin was hard-tied to this USB active signal. This mean that having VBUS high was required for the USB transceiver to communicate.
On EFM8UB1 devices, there are two options:
In the second case, connecting that VBUS / GPIO pin to the USB connector is not required.