Raster interrupt


 * 1) Disable interrupts with the SEI instruction.
 * 2) Enable the raster interrupt; set bit 0 at $D01A (the VIC-II interrupt enable register) to 1.
 * 3) Enter the scanline on which you want the interrupt to occur.  Low bit is written at 53264, and the high bit at 53265.
 * 4) Provide the address of the interrupt routine.  Low bit of address is at $314, high bit at $315.
 * 5) Re-enable interrupts using the CLI instruction.

Note that the raster interrupt is the same as the hardware timer. You may want to disable the hardware timer interrupt by putting a vlue of 127 at location 56333 (but remember to store the contents of the old interrupt first.)