Changes

Scanning is done in single scanlines (one pixels height). The scanning procedure waits while FBEFh.Bit2=0 (which probably indicates that the head is in the left-most position, or that it has just leaved it, or so). The horizontal "dot clock" is implemented as software delays. When scanning a black dot, one or more bits in Port FBEFh become non-zero (not sure which onesbit; the driver software simply checks "IF Port[FBEFh]<>FFh THEN PLOT pixel").