Post by Jeff Ledger on Dec 29, 2007 23:56:21 GMT -5
Could someone who understands the C64 better than I explain the nature of the screen editor in the 64? As I understand it, each change of the screen was a direct change in screen memory? Something far ahead of the competition at the time. The reason I'm trying to understand it, I would like to replicate it on the Prop.
"Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe." -Albert Einstein
Post by David Murray on Dec 31, 2007 10:28:24 GMT -5
I uderstand it pretty well, but I'm not sure what part you have a question about. In fact, I'm a bit confused by that statement "Something far ahead of the competition at the time." Because as far as I know, the only systems that didn't do it this way would be the Atari 2600 and maybe the Timex Sinclair since their screens were CPU driven.
Yes, when you type, all you are doing is modifying the screen. When you press RETURN the editor looks at the line the cursor is on then "re-reads" the line(s) from screen memory and enters it into your program as if you had re-typed it. There is a "screen line link table" in zero page that keeps track of which lines wrap to the next line.
A common mistake is to edit multiple lines on screen without pressing RETURN. If you don't press return your edits will be lost.