How to connect a SilentStepStick TMC2130 stepper driver? please excuse the noob question

Am connecting a SilentStepStick to arduino with a stepper, for bench testing. 

It requires 5V power, plus I have a 24V power supply for the steppers.
+5V connected to Vio, and +24V connection to VM.  

Question: how to connect the grounds?  The device has two GND pins.  Should I just connect one ground, from the 5V power supply, to avoid ground loops?    

Or should grounds from both power supplies be connected?

Thankyou for any advice.
Answer: (from Electrical Engineering), yes both grounds must be connected.  

In this example, +5V and GND from the arduino would connect to the two top left pins in the diagram (Vio &amp; GND).  

The two 24v power lines would connect to the bottom left two pins, Vm &amp; GND