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0x64 ( 100 )  Vertical Line Count Offset
  
BitsDescription
7:0Offset added to the vertical line counter affects copper, line interrupt and active line count.

* Since a change in offset takes effect when the ula reaches row 0, the change can take up to

Notes:
  Normally the ula's pixel row 0 aligns with vertical line count 0.  With a non-zero
  offset, the ula's pixel row 0 will align with the vertical line offset.  Eg, if the offset is 32
  then vertical line 32 will correspond to the first pixel row in the ula and vertical line 0
  will align with the first pixel row of the tilemap and sprites.
  one frame to occur.