Limitations
The vertical extent of the entire display can vary between 0 and 240 scanlines - this depends on what number of lines the ANTIC is programmed to display according to the display list. The horizontal width of the screen can be programmed to be 256, 320 or 384 pixels wide (in the widest mode, only 352 pixels are really visible).
Horizontal fine scrolling can move the scrolling region up to 16 color clocks.
Vertical fine scrolling can move the scrolling region the number of scan lines in a single Mode line of the scrolling region, up to a maximum of 16 scan lines.
Although ANTIC's Display List program counter is 16-bit, only 10 bits are changed during normal (i.e. sequential) execution of the Display List. This means the Display List requires a JMP (Jump) instruction to cross a 1K boundary. This is not a serious limitation, because the size of a single display list usually varies from 32 to 202 bytes, and virtually never exceeds 720 bytes. Since it can be located anywhere in the memory, there is little difficulty finding a sufficiently sized place in memory that does not cross a 1K boundary.
The Memory Scan Register, a register addressing the data stored in the screen memory, is 16-bit, but only 12 bits are changed when ANTIC is sequentially scanning the video memory. This means the Display List requires a Mode line instruction with the LMS (Load Memory Scan) option added where screen memory crosses a 4K boundary. ANTIC's graphic modes E and F require more than 7.5K of screen memory for a full screen display. The Display Lists for these displays require the LMS option added to a Mode instruction near the middle of the display where screen memory crosses the 4K boundary. Note that the 4K boundary cannot be crossed within the middle of a Graphics Mode line. The 4K boundary address can only be crossed between the end of one Mode line and the beginning of the next line. In other words, the memory for the previous Mode line ends at the exact last byte of the 4K block and the next Mode line begins at the exact first byte on the other side of the 4K boundary.
The character set can be located anywhere in the memory (see CHBASE), but, depending on the ANTIC Text Mode it has to be aligned to a 512-byte or a 1K boundary.
The Player/Missile memory map may occur anywhere in memory (see PMBASE), but must be aligned to a 1K or 2K boundary depending on the resolution (see DMACTL).
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