== Programmable raster interrupt ==
The 8-bit memory-mapped register PRI register (at address 6800h) specifies the scan line where the interrupt occurs. The interrupt will occur at the end of that scan line. Setting this register to 0 (the default value at power-up) reverts to the classic [[Gate Array]] R52 raster interrupt system instead.
PRI can be reprogrammed as required to produce multiple interrupts per frame.