This is very clever. Everyone else is doing scopes in X-Y . I only read 16F84 asm code, but it appears you draw vertical lines 16 times to make them visible. Very good. My hat's off to you. I've been doing X-Y Laser Graphics (actual laser on a screen) since the 80's. After all these years, I finally put my D/As into a scope. I also see a difference between your ASCII and image schematic values.
Regards, Steve, Retired EE & Laserist. Dropping sec, 8 bits is all U need for X-Y! 16x16