Hi @shiroifuyuki, thanks for your question and welcome to the Community page. Let me share some information about DYNAMIXEL and XL-320 that should help you get started.
DYNAMIXELs use asynchronous serial communication- this means that the XL-320 sends and receives signals over the same data line. If it’s only connected to a TX pin, your Arduino won’t be able to receive any feedback or signals from the XL-320.
While XL-320 uses “TTL” transistor-level communication, because it is asynchronous you will need a communication circuit to provide the appropriate TX/RX switching. The online e-Manual (emanual.robotis.com) for the XL-320 shares the needed communication circuit here: https://emanual.robotis.com/docs/en/dxl/x/xl320/#ttl-communication
ROBOTIS also manufactures Arduino shields that provide the needed communication circuits here- DYNAMIXEL Shield (for Arduino Uno & “1.0” pinout) and DYNAMIXEL Shield for Arduino MKR Series.
Once you have the physical connection to your Arduino taken care of with the appropriate communication circuit, I would recommend downloading our Dynamixel2Arduino and DynamixelShield libraries.
If you are using one of our shields, you can use the DynamixelShield libraries and start with those examples. If you use your own communication circuit, it’s best to use the libraries and examples from Dynamixel2Arduino.
Some more YouTube videos showing using DYNAMIXEL with Arduino can be found through the ROBOTIS Customer Support YouTube channel here in this playlist.
Hopefully this information is of assistance- please let me know if you have other questions.