Hello.
I moved your post to the motor controllers/drivers and motors support category since it is more appropriate here.
The RX and TX pins do not connect or correlate directly to the motor outputs like your questions suggests. You can think of each Tic as having two main components, a microcontroller and a stepper motor driver. The RX and TX pins (as well as most of the other control interface pins except STEP and DIR) connect to the microcontroller on the Tic. When you use the Tic in serial mode, your Arduino and the microcontroller on the Tic communicate via serial protocol. (If you are using our Arduino library for the Tic, you can see a list of the available serial commands here.) Based on the commands your Arduino sends, the Tic’s microcontroller generates the STEP/DIR signals required to control the stepper motor driver accordingly. In the case of the Tic T825, the driver is the DRV8825, and that is what controls the motor outputs.
- Patrick