I'm not sure how to ground the L293D Motor setup I'm using

Question

According to Texas Instruments, the L293D has the following setup

Enable 1, 2 Driver Channels (5V) [   u   ]  Chip Power (5V)
                  Driver Input 1 [       ] Driver Input 4
                 Driver Output 1 [       ] Driver Output 4
                        Ground 1 [       ] Ground 4
                        Ground 2 [       ] Ground 3
                 Driver Output 2 [       ] Driver Output 3
                  Driver Input 2 [       ] Driver Input 3
               Motor Power (12V) [       ] Enable 3, 4 Driver Channels (5V)

Where the u in the middle top represents the divet present on the top of the motor driver to tell which side is "up."

For my project specifically, I will strictly only be needing the left side motor control logic (1, 2) and since I am not running a DC stepper motor, I will only run the following two states (i.e. I want output 1 to always be the +12V and output 2 to behave as the ground, or for no current to be flowing at all):

I) [OFF] Input 1: Low | Input 2: Low
II) [ON] Input 1: High | Input 2: Low 

Therefore, here is my partially completed schematic of the system (top is now on left side; Ground is the middle two pins on the bottom side of the L293D in the schematic).

Now according to the tutorial I am following, I should just ground 1 and 2 back to the Pi. However, my concern is that that would cause a problem because the motor powering circuit is powered by a 12V supply. Hence, should I ground 1 and 2 back to the Pi (bottom)? or Back to the Ground for the 12V circuit? (at the top).

Thank you and much love!

Answer 1

Ground is the reference voltage for all circuitry. In effect all the grounds form a single point.

You need to connect at least one Pi ground to a L293D ground.