     PAL-Timing scheme for a normal scan line, no sprites on the current scan line
     but at least the sprites 1+2 active on the following scan line:

      +---------------------------------------------------------------+
      |         1         2         3         4         5         6   |
      |123456789012345678901234567890123456789012345678901234567890123|Cycles
      +---------[------(--------------------------------------)---]---+Borders
      |3-4-5-6-7-rrrrrgggggggggggggggggggggggggggggggggggggggg--0-1s2s|Phi-1 VIC
      |                                                           ssss|Phi-2 VIC
      |xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxXXX====|Phi-2 CPU
      +---------------------------------------------------------------+

      "-" = idle bus cycle (reads from the last byte of the video bank)

       <num> = pointer fetch for sprite <num>  ;  g = graphics fetch
       s = sprite data fetch  ;  r = memory refresh cycles

       x  = processor executes instructions (BA high, AEC high)
       X  = bus request pending, bus still available (BA low, AEC high);
            processor may execute write cycles, stops on the next read cycle.
      "=" = bus unavailable (BA low, AEC low); processor is blocked because it
            would like to read something.