the RJ11 port connects directly to the CPU (HC11). This is old hardware, so the com port connects directly to the CPU and is used to communicate directly with it. We were told by the original devs it is possible, but they are not willing to make any changes for us, so we have to resort to...
To answer some things here: We currently can use picocom to communicate via the RJ11 port on the mainboard. We built a USB -> modem cable that has the proper transistors. We are able to see the game communicate and we are able to talk to it as well, it is just that we do not know what it is...