Late 70's. I wrote the operating system for the Control Pak EM system sold as the Barber Colman Network Supervisor building automation system. Thousands of systems were installed and many are still in use. By cracky. Er, what was the question again?
I left the company in '87 and lost contact with them years ago. The system was 8085 based, ran a preemptive RTOS written in PL/M and assembler derived from RMX-86. The network was optically isolated RS-485 9600 baud. It was configured using Template Block programming, where the blocks acted like little HP RPN calculators that were linked together to build a control sequence. Its primary distinction was its ability to do user generated "direct digital control logic". The OS fit in 32k.
Barber Colman OEM'd the main logic board from Control Pak and put them in their own box.
Barber Colman's QC engineers were hard core SOB's and they put that system through the wringer, trying to break it in a million ways. They had a special smile when they had found another bug or a screw terminal they could zap with a spark generator and lock the system up. They were unhappy when they could not break it anymore. That's why there are still some Supervisors running today. They are tough as nails. I owe those guys a lot.
I do software consulting in building automation and control systems, but mostly I build a mouth operated game controller for quadriplegics called the quadstick. That has been the most fun thing I've ever done.
http://www.controlpak.com/network.htm