I wonder if that is a TI930 video terminal. If so, amazing it is still working after all these years. TI930 and TI911 terminals are not serial, current loop or anything like that. It's their own protocol.
In Chicago 10 years ago I met a guy who had been implementing an ASP.NET rewrite of a customer's insurance system that was running on a DNOS TI-990.
he said the 80-something year old programmer would still come into the office a couple of times a week, and they had a young guy that was able to keep all the kit running, because you can still repair those machines using off the shelf TTL logic.