ANTIC - The Display List

The Display List

The Display List is the list of instructions, or the program, directing ANTIC how to generate the display. The Display List and the display data are written into RAM by a 6502-compatible CPU. ANTIC retrieves Display List instructions and screen memory from RAM using a technique known as direct memory access (DMA). Once a program sets up the Display List instructions and screen RAM ANTIC automatically takes care of generating the screen display. This powerful design allows the Atari 8-bit computers to produce complex, mixed-mode displays without direct CPU intervention while other platforms, even those designed much later, cannot either mix graphics modes in one display, or do so without direct, complex CPU interrupts.

ANTIC processes the higher level instructions in the Display List and translates these instructions into a real-time stream of graphics data to the CTIA/GTIA chip which provides the color. Together the two chips provide 6 text and 8 graphics modes (14 total). The more advanced version, GTIA, provides three alternative color interpretations for each graphics mode providing a total of 56 (14 times four) graphics modes. However, only the ANTIC graphics modes based on half color clock pixels are capable of expressing the complete color palette provided by the new color interpretations, and of those modes only ANTIC mode F (320 horizontal pixels) is convenient for use. Thus 17 (14 + 3 additional color interpretations for mode F) recognizably different graphics modes are available.