Lower row of pins where the MMU cable connects to the main board ? Serial Port?  

Lower row of pins where the MMU cable connects to the main board ? Serial Port?

On the Mk4 the MMU3 Cable connects to the upper row of pins on a connector near the top of the electronics box (the xBuddy). But there is another row of pins directly below what you plug the MMU cable to. On the Mk3 that lower row of pins include a TX and RX of a serial port, plus power and ground and one other pin. Is the corresponding lower row of pins on the Mk4 ALSO for TX and RX of a serial port? I haven't been able to find info on that anywhere, yet. I'm using that serial port on my Mk3 for a special use and am planning on migrating over to the Mk4, so I'm hoping those pins on the Mk4 are the same as the pins on the Mk3. Does anyone know?

Is there any diagram or picture that shows the actual functions of those pins?

Also, it does seem that they are NOT USED on the Mk4, so is it safe to assume that I can make use of them, along with the modifications I'll be making to the firmware, as I've already done on my Mk3?