I worked on this system during its development in the 1980s.
There were actually two PDP-11s, the one to run the platform displays running locally-written software.
The “weird control sequences” sent between the PDP-11 and the plaform displays were HDLC, a synchronous protocol then common in IBM token ring networks as SDLC. This was actually a decent technical solution because they only had to run one coax cable down each train line and the PIDS could sit there watching for their token slot. The hardware for HDLC would have been commodity, whereas fibre optic or carrier sense for long-run packet was not.
The other PDP-11 that ran the signals (the “train describer”) could plot the position of trains on glass TTY terminals using escape sequences (VT100, same as in xterm today) so our PDP-11 pretended to be one of those and screen-scraped. So I was told, when I asked the guy who wrote it.
All of that was done before I got there. I was called in with 6 weeks to go before commissioning to fix the bit in the middle that recalculated train positions and arrival times.
There were actually two PDP-11s, the one to run the platform displays running locally-written software.
The “weird control sequences” sent between the PDP-11 and the plaform displays were HDLC, a synchronous protocol then common in IBM token ring networks as SDLC. This was actually a decent technical solution because they only had to run one coax cable down each train line and the PIDS could sit there watching for their token slot. The hardware for HDLC would have been commodity, whereas fibre optic or carrier sense for long-run packet was not.
The other PDP-11 that ran the signals (the “train describer”) could plot the position of trains on glass TTY terminals using escape sequences (VT100, same as in xterm today) so our PDP-11 pretended to be one of those and screen-scraped. So I was told, when I asked the guy who wrote it.
All of that was done before I got there. I was called in with 6 weeks to go before commissioning to fix the bit in the middle that recalculated train positions and arrival times.