In a recent episode of 8-Bit Show & Tell, the spotlight was on an often-overlooked feature of the Commodore 64’s VIC-II video chip—its ability to extend the screen border across the entire display. With a simple control bit, the border color can fill the entire screen, essentially turning it into one giant pixel. But, of course, things aren’t quite that simple when you start factoring in the dynamic interplay between the 6510 CPU and the VIC-II.
That seemingly basic border color register, found at memory location 53280 (or $D020 in hexadecimal), is capable of much more than just painting the screen a solid hue. When manipulated alongside precise CPU cycle counting, it becomes a tool for deeper experimentation and understanding of the C64’s inner workings. By modifying this register in real-time, enthusiasts can create stunning effects, push the hardware in unexpected ways, and gain insights into how the system processes graphical data.
This kind of discovery is what makes retro computing so fascinating—it’s not just about nostalgia, but about pushing classic hardware beyond its intended limits.
