|write only||54276||$D404||HSCROL||Horizontal Fine Scrolling||both|
If this location is set to a value other than zero, the ANTIC omits that number of color cycles in that line. In other words, ANTIC start displaying that number of color cycles line "later", the picture is shifted "left".
Only the lower 4 bits of this register are used, so the maximum value is 15.
This register should not be altered while ANTIC is drawing the screen. It has to be changed during vertical blank interrupt to get good results.
to be added: table showing antic modes and maximum value for each mode.