one or two dozen lines which takes a trivial amount of time in assembly. So, if this scrolling process involves a full screen Mode 2 or Mode 4 text display (rather worst case) and uses the entire 4K capability of ANTIC's automatic screen memory addressing, then the horizontal scrolling can continue in this manner for about 3,000 steps; equivalent to 75 full screens. However, even the 4K memory use is not required. After all the data from the first full screen has been shifted off the display the scrolling application can rebuild the first screen to contain a known transition point so that the scrolling action can jump back to the first address in the block with no apparent stutter or obvious interruption in the scrolling. Fine scrolling this arrangement requires a little more planning. When fine scrolling is enabled in the Display List ANTIC retrieves more information than the Mode line requires for display. As each mode line now uses more memory, the new information scrolled into the side of the display is not the byte/character that was displayed at the start of the next line. However, this does not impair the scrolling process and merely changes the value of addition and subtraction used to locate the start and end of each display line. Display List Interrupts (DLI) ANTIC includes a feature to trigger a CPU-serviced interrupt at specific vertical positions on the screen. This is built into the ANTIC Display List which directs ANTIC to launch the interrupt during the last scan line of the current Mode instruction, and so is called "Display List Interrupt". Other platforms call this activity, "Raster interrupts", or "Horizontal blank interrupts". The usual purpose is to change display-related values at a known location so transitions are visually precise or occur where they will not conflict with display activity. Possibilities include, but are not limited to changing color register values, Player/Missile horizontal positions, and fine scrolling values. Since the DLI is 6502 machine code executed by the CPU, any kind of processing work is possible provided it is short enough to not conflict with other activity and does not overrun a subsequent Display List Interrupt. A good example is mouse controller polling which must be done more frequently than 1/60th of a second. Overview Properly launching the interrupt requires the following conditions: A Display List with a Mode instruction that includes the Display List