My board communicates at 57600 baud, no hardware handshaking. I have the pins for handshaking brought out to pad in case I want to experiment with them.
The TX pin on the slot is the Mac transmitting out. So, that should be wired to your microcontroller's RX pin.
And it follows that RX on the slot is the Mac receiving in. So, that should be wired to your microcontroller's TX pin.
By the way, there is a definite limit to the amount of power you can draw from 5V trickle. 5 ma I think. If you exceed that too much, the Mac shuts down almost immediately at power up.