03. Irq (irq) - RetroAsmDev/C64AsmGameJourney GitHub Wiki

Classic example of use of the CIA interrupt (60 times / second) to call own routine.

We need only:

• Change the address of the routine that handles the IRQ on address $314 (LSB) and $315 (MSB)
• Ensure that SEI and CLI instructions are used during that change
• Once own code is executed jump to the original KERNAL routine address $EA31

Our own code just changes the border color, so in effect it looks like it is blinking. It cannot be seen on the screenshot, since there are always only two colors on the screen: