Question:

Is it possible to detect a break condition on the UART RX line when using the EFM8 UART0?  If so, is there a software example that demonstrates this?

Answer:

While the EFM8 UART0 module itself does not support break detection, and we do not have any software examples that demonstrate this exact application, it should be fairly straightforward to modify one of our existing examples for the pulse counter array (PCA) to detect a break condition.

By externally routing the RX data line to a separate MCU pin (on your PCB) and using the crossbar to select that pin as a PCA input, you can use the input capture mode of the PCA to detect the break condition on the line.  A good starting point for this application would be out firmware example "EFM8SB1 PCA0 Capture Input," which you can access through Simplicity Studio under the EFM8SB1 software examples.