I have a similar question.
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I want to use the Deskcnc board with gecko 320 servo drivers. I have mapped out most of all the connections but the one that seems to confuse me is the ground and +5Volt that is found on the DeskCNC controller, and the common/+5v on the 320 card. I have a sys3A from Imservice and I have opened it up to look at how they put wired everything up. It appears they tied the common on all the servo boards together, and then they came off the ground of the Deskcnc board over to the just z axis board and they but the lead coming out of the +5V of the Deskcnc board. I'm very confused but this is the only thing that is holding me up in drawing out my connections.