serial gateway mode without using USB connector?

I’ve got the dash doing what I want from e.g. rasberry pi using micro USB and serial gateway mode.

Now I want to control it from an Arduino instead. Note that I don’t want to run my arduino microcode on the dash itself – I want to treat the dash as a controlled peripheral on the serial bus.

What pins do I need to use to do this? Here are my guesses/thoughts so far based on looking at the datasheet:

For power: connect to VBATT with the arduino source voltage ok (e.g. 9V)? The datasheet under Operating Conditions doesn’t give min/max voltage for this pin in DC Mode.

The for the serial connection do I want S0TX/S0RX or S2TX/S2RX?