I use a Prolific branded USB to to 9-pin serial adapter connected to a MacBook Air going through a null model (with some internal doctoring, as I recall) to talk to a 25-pin D serial connector on my old Deckel FP2NC with Dialog 4 control. I use the terminal emulator app "Serial" to talk to the Deckel. The communication is reliable at 2400 baud, less so at 9600 baud. I use 8-bit, no parity, and 1 stop bit with no traffic control. This is by far the easiest setup I have found for talking to the Deckel compared to several generations of old Windoze machines with built-in serial ports. The Serial app is comparatively idiot-proof. No more drinking around with COM port numbers or any of that drivel.
I have no problems sending the Deckel CAM output from the Fusion 360 post I have modified for the Deckel, and bringing g-code back from the Deckel for modification or archiving. (256k RAM only goes so far, after all.)