Sorry I am not Will
But the TX_data, RX_data, and Direction_Port are three IO pins that are needed from your dev board or the like.
In particular the Dynamixel Servos use a Half duplex protocol, that is TTL data pin goes to you dynamixel servos and it carries the Serial data to and from all of the servos.
You need to have the direction port set to know which direction the data should be going. That is are you sending data from your host to the servos or receiving data form the servos.
Your controlling software needs to be knowledgeable enough to know when to set and clear this IO signal. Most of the time the code will do something like:
digitalWrite(Direction_Port, HIGH); // assumes HIGH is for TX, may be low
<Do Serial.writes to output your packet>
DynamixelSerial.flush(); // make sure the TX fully completes
digitalWrite(Direction_Port, LOW); // go to RX mode.
And you need to make sure to not do this when you are expecting a servo to respond, or your packet will collide with the data the servo is trying to send.
Hope that helps