Studer A820 serial remote controller

[geovar]

I'm negotiating to buy an A820 MK I and among other things there is also a Serial Controller, but the connecting cable is missing. On the controller there is a serial socket Male, and on the A820 3 Ports,see photo. Which port should I use? Serial to SerialContr.> (SMPTE/BUS RS232) or Serial Contr.> >PARALLEL REMOTE on the A820, or the Auto Locator on the A820?
Thanks
George