$D01A/53274/VIC+26: VIC Interrupt Mask Register (IMR) 1 = IRQ enabled (IMR) +----------+-------------------------------------------------------+ | Bit 7 | 1 = if you want to set another bit(s) | | | 0 = if you want to clear another bit(s) | | Bit 3 | Light-Pen Triggered IRQ Flag | | Bit 2 | Sprite to Sprite Collision IRQ Flag (see $D01E) | | Bit 1 | Sprite to Background Collision IRQ Flag (see $D01F) | | Bit 0 | Raster Compare IRQ Flag (see $D012) | +----------+-------------------------------------------------------+ An IRQ will be initiated, if equal bits are set in IRR and IMR. If you set or clear specific bits in $D01A, the others remain untouched.