Wiring ATX Power Supply for PS_ON

I want to control my ATX power supply with the M80 and M81 commands but am confused by how to do the wiring to the RAMPS board. I currently have a switch connected that connects ground to the on/off pin of the ATX power supply. Close that switch and on comes the ATX. I had assumed that the PS_ON pin would behave in the same manner...issue the M80 and I would see the circuit between the PS_ON pin and ground close. M81 would then open it. It does not seem to function in this manner. I do note that when the M80 command is issued a 5V supply is available between PS_ON and the VCC pin above it. M81 turns that supply off.

How do I wire the ATX into this?

Regards,
Wisar

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Thanks. I had missed that post but still understood that the green wire needs to be connected to PS_ON. What I did not understand was the behaviour of the readings that I was getting. With M80 triggered I was expecting a closed circuit between PS_ON and ground...which is what my mechanical switch delivers. Unless I was metering something wrong I did not see that...however....when I connect it (with my switch still in series as an physical overide for OFF) it all works so all is well.

Wisar

It think it just joins one of the ground wires from the psu (the 12v and ground) to the pin when M80 is triggered and disconnects them when M81 is triggered.
The 5v and VCC pins are for powering the servo pins (to the left) via the Arduino if you put a jumper between them.
Only reason I can think the M81 would stop the 5v is if it was to prevent the Arduino powering the shield, which wouldn't make any sense as if the Arduino was powered via the 12v M80 would be void as it would disable itself.

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Hi guys, I am looking for suggestions on how to connect my sanguinololu 1.3a so that as I load my G code starting with g80 added as a preliminary when sliceing (I think) the atx power is turned on i.e the green wire connects to the black and 12 volts are produced and again after the print job finishes, the hotend parked and the bed and hotend powered off, a final Gcode command g81 (I think) will disconnect the black and green control wires and the 12 volt is turned off. My thoughts are to connect the black and green wires across a relay but I do not know which pin is accessed by the G80 and G81 code to use to energize the relay coil which will make or break the relay contact. Can someone please advise