=== 6845's MA ===
NOTE: It seems the The 6845 has an internal "stored" MA. The current MA count is reloaded with this value at the start of each line. There are 3 times when this value is updated:
# When the split screen address is set, split screen line has been reached and Horizontal Counter equals Horizontal Displayed.
# When Raster Counter + Soft scroll matches R9 and Horizontal Counter equals Horizontal Displayed.