Narrow width ANTIC fetches the screen RAM needed for Normal width. Likewise, for Normal width ANTIC fetches the screen RAM needed for Wide. ANTIC buffers the first few bytes read from screen memory that are sufficient to cover the 16 color clock range of movement. (Two to four bytes depending on display mode.) The HSCROL value specifies how many color clocks should be output from the buffered data beginning from the last (right most) color clock of the last buffered byte and progressing to the left. When HSCROL is 0 no color clocks are output from the buffer, so the first screen byte displayed is the first byte after the buffered data. As HSCROL increases more color clocks from the end (right side) of the buffered data are added to the left edge of the display causing the fine scroll shift to move the screen contents to the right. ANTIC Mode F (high-resolution, 1/2 color clock pixels) can only be scrolled two pixels at a time, because HSCROL specifies color clocks. ANTIC Modes using the alternate GTIA color interpretations must be scrolled by an entire GTIA pixel (two color clocks). Only even values should be used to ensure correct scrolling. Odd values of HSCROL will shift the pixel stream into a different state that GTIA will interpret as different colors. Unlike many platforms Atari's horizontal scrolling is visually consistent and free from color "strobing" artifacts due to Atari's pixel size matching the color clock timing needed for accurate color. VSCROL $D405 Write Vertical Fine Scroll This register specifies the distance of the Vertical fine scrolling in scan lines. The lowest 4 bits are significant, however the Vertical scroll value should range from 0 to the ANTIC Mode line's scan line height - 1. Scrolling farther than the ANTIC Mode's number of scan lines results in lines of repeated data upsetting the fine scrolling continuity (though, this can also be used as an exploitable behavior). The Vertical scrolling region is defined by setting the VS bit ($20) on a sequential series of ANTIC Mode Lines in the Display List. The first Mode line without the VS bit set becomes the end of the scrolling region and is used as a buffer line to supply the new information to scroll up into the bottom of the scrolling region. The Vertical scroll value indicates the scan line number to begin the display in