There are three kinds of Legacy Communications today:
- Teletype: Like Danfoss ZX/NC25. Data scrolls down page. When the bottom is reached, the screen moves up a line. Any time new data is required, the entire screen is repainted. Slow!!
- Terminal: Like Com-Trol 4000/5000, RMCC, EIL. Uses escape sequences to position the cursor on screen, then prints characters. Allows for painting the screen once, then repainting pertinent data. Faster, cleaner, & effective, but requires a terminal that with the escape sequences.
- Protocol: Like Danfoss AKC-55, CPC Einstein. Uses a coded sequence of questions/answers to gather data, requires specific algorithms to turn this data into screens. Protocols are not public, but aren’t state secrets, either. Fair use laws allow for reverse engineering.
Legality: Teletype & Terminal modes are known as ‘Screen Scraping’. There is NO legal barrier to these techniques. For protocols, once controller companies sell a device, they can’t block owners talking to it. They don’t have to help, but they can’t complain. It’s in the public domain, since protocols aren’t copyrightable. As always, though, cooperation is better than confrontation.
