The thing to keep in mind with these older WeatherSTAR units is they are essentially "dumb". They are just character generators that can be addressed over satellite... so, if memory serves, a Digital PDP-11 mainframe at TWC would create slightly modified UK Teletext packets to send to the STARs, addressing a specific unit that is hooked up to the satellite feed.
As an example, imagine you have a WeatherSTAR III unit who's address is 00011111 in Denver, and a WeatherSTAR Jr with address 00022222 in Minneapolis. Both units are hooked up and connected to a VideoCipher II that has been authorized by TWC. The mainframe at TWC would gather all of the necessary weather data, 36 hour text forecasts, etc, and build pages to push to the units. The mainframe would fetch the information for Denver, and create a page header packet specifying how many lines should be on that page with some other information, then packets would follow it with what text should be displayed on what line. These packets would be addressed to unit 00011111, and sent over the satellite. Then it would do the same thing for Minneapolis. Gather the necessary information for Minneapolis, and create packets to address unit 00022222. The mainframe defines exactly what will be seen on-air. "Conditions at Denver" could be changed to "Your weather for Denver", or whatever else in the current conditions product... if they made that change at the mainframe.
I hope that makes sense. It's not an in-depth explanation, and there are a lot of technicalities -- but that's just a dumbed down example of whats going on behind the scenes. The 4000 operates a bit differently, but it follows the same premise. It's addressed by the mainframe, and just displays whatever is sent to it. This is why during sun outages, you would see random characters appear on these older STARs... because the data packets are getting screwed up.
Information overload. But that's the basic run down. I might do a little write up here of my WeatherSTAR III and the road taken to make it run again with the combined efforts of Techknight and a few other forum members on here... that way I don't clog up the 4000 topic with III/Jr stuff
Edit: Here's an example off of my YouTube channel. I'm sending these lines to the unit... totally custom page I built. Only example of this that you'd see in the field was back in the early 80s when they'd advertise upcoming programming, or show that eclipse warning from like 1984 or something around there.