Need a robust way to change uart lines

I’m working on a project where I am sending data from an msp430 to an atmega328 through regular tx/rx lines. My board will also need the capability to perform software changes on the atmega through FTDI, which needs to be connected to the same tx/rx lines. So when the FTDI is connected, I’ll need to break the lines from the MSP. My first thought was just to put a PMOS between the two lines and have the FTDI VCC connected to it. But I am not sure this would be the most robust solution. Can any one point me to the right direction?

Thanks,
Micah