yeah, it seems the board had some sort of serial connection. its emulation is probably beyond my current set of skills, though (my frustration with MegaDrive serial EEPROMs exposed that I clearly suck at understanding serial comms from the running code), so if you want to take a look, the relevant slot device is at src/mess/machine/sns_event.c
We'd probably need a dump of the mcu prom (
which looks like it'd be possible) because as Logan says, I don't actually know what it does or if it's even a serial port.