wiring for 4-wire motor & Gecko drive

Hi,
I'm wiring up a 4 wire step motor to a Gecko 201A. The motor has 4 wires
(A, -A, B, -B), and a "ground" wire.
Does anyone know if the "ground" wire from the motor should be connected
to the "Power Ground" wire on the Gecko drive, or is it to be connected to
an "earth ground"?

Thanks,
Rick