The console in question is PC-Engine (Turbografx-16 in the US).
I have a game that is displaying both horizontal and vertical text. I've figured out the control codes and most of the pointers for both - sadly, I don't think the horizontal vs. vertical printing is determined via control code.
I'm aware I might have to delve into asm (a new thing for me) to figure it out, but any beginner's tips for solving this kind of problem?
Ideally, I'd be replacing all instances/calls to creation of vertical text with the routine that prints horizontal text. The vertical text is stored in rom almost identically to the horizontal - I can point a vertical string to read a horizontal one and vice versa with minor formatting changes.