== Programmable raster interrupt ==
The PRI register (at address 6800h) specifies the raster line where the interrupt occurs. The raster interrupt will start exactly 10us following after the HSYNC start on that raster line. Unlike the R52 raster interrupt system, it is not dependant on the width of the HSYNC.
Setting the PRI register to 0 (the default value at power-up) reverts to the classic [[Gate Array]] R52 raster interrupt system instead.