Changes
/* 6845's MA */
NOTE: It seems 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:
1. When the split screen address is set, split screen line has been reached and Horizontal Counter equals Horizontal Displayed. 2. When Raster Counter + Soft scroll matches R9 and Horizontal Counter equals Horizontal Displayed. 3. When Vertical character count is reset to 0, it is then loaded from R12 and R13.
It is therefore possible to simulate split screen, by setting the soft scroll at the time correct time, then setting it back to 0 immediately after.
