Here’s a whiteboard tutorial on programming the 80-column screen on the Commodore 128. It’s very different from the 40-column VIC display, since you have no direct access to 80-column screen memory and have to program it indirectly by reading and writing to the VDC’s registers, which requires a handshaking process through a pair of registers at $D600 and $D601 in the C128’s I/O block.

There will be another video soon demonstrating how to use the little routines here to do actual work.