ANTIC

Alphanumeric Television Interface Controller (ANTIC) is an LSI ASIC dedicated to generating 2D computer graphics to be shown on a television screen or computer display. Under the direction of Jay Miner, the chip was designed in 1977–1978 by Joe Decuir, Francois Michel, and Steve Smith for the Atari 8-bit computers first released in 1979¹. The chip was patented by Atari, Inc. in 1981. ANTIC is also used in the 1982 Atari 5200 video game console, which shares most of the same hardware as the 8-bit computers. For every frame of video, ANTIC reads instructions to define the playfield, or background graphics, then delivers a data stream to the companion CTIA or GTIA chip which adds color and overlays sprites (referred to as "Player/Missile graphics" by Atari). Each ANTIC instruction corresponds to either blank scan lines or one of 14 graphics modes used for a horizontal band of the display. The height of each band depends on the mode. The instructions comprise a display list, in Atari parlance, which specifies how the entire display is built from a stack of individual modes. The display list specifies where the data for each row comes from. For character modes, the base address of the character bitmaps is stored in an on-chip register and can be changed. Display list instructions can enable horizontal and vertical fine scrolling and mark that an interrupt should occur.…

Alphanumeric Television Interface Controller (ANTIC) is an LSI ASIC dedicated to generating 2D computer graphics to be shown on a television screen or computer display. Under the direction of Jay Miner, the chip was designed in 1977–1978 by Joe Decuir, Francois Michel, and Steve Smith for the Atari 8-bit computers first released in 1979. The chip was patented by Atari, Inc. in 1981. ANTIC is also used in the 1982 Atari 5200 video game console, which shares most of the same hardware as the 8-bit computers. For every frame of video, ANTIC reads instructions to define the playfield, or background graphics, then delivers a data stream to the companion CTIA or GTIA chip which adds color and overlays sprites (referred to as "Player/Missile graphics" by Atari). Each ANTIC instruction corresponds to either blank scan lines or one of 14 graphics modes used for a horizontal band of the display. The height of each band depends on the mode. The instructions comprise a display list, in Atari parlance, which specifies how the entire display is built from a stack of individual modes. The display list specifies where the data for each row comes from. For character modes, the base address of the character bitmaps is stored in an on-chip register and can be changed. Display list instructions can enable horizontal and vertical fine scrolling and mark that an interrupt should occur. An interrupt allows arbitrary 6502 code to execute, usually to change display-related settings in the middle of a frame. Atari computer magazine Antic was named after the chip. Example: Given an eight scan line ANTIC Mode (Text Modes 2, 4, or 6) with the VS bit set on two adjacent Mode lines the scrolling region then consists of three Mode lines—the third line in the scrolling region is the first Mode line encountered without the VS bit set. When Vertical scrolling is not set in the Display List the three Modes lines would naturally result in 24 displayed scan lines. When the VS bits are set in the Display List Mode instructions as described and the VSCROL value is set to 2 then the first Mode line in the region begins displaying at scan line 2 showing scan lines 2 to 7 (six scan lines or 8 - VSCROL), the second Mode line is displayed completely (eight scan lines), and the final Mode line ends at scan line 2 showing scan lines 0 to 2 (three scan lines or VSCROL + 1). The total scan lines displayed in the scrolling region is then 6 + 8 + 3 = 17 scan lines. Since fine scrolling is based on scan lines not pixel height, and scrolling region movement is done simply by skipping scan lines from the first Mode line and adding scan lines to the last Mode line, it is possible to use different graphics Modes within the scrolling region. This merely requires additional care when determining how many scan lines can be shifted for the current first and last Mode lines in the scrolling region. Blank Mode lines cannot be contained within a scrolling region, because Blank Mode line instructions inherently do not have a Vertical Scroll Modifier bit. (Blank Mode line instructions specify the blank line count using the bits 7 through 5 that function as LMS, HS, and VS Modifiers for "regular" Playfield Mode instructions.) However, a Blank Mode instruction can be used to end a scrolling region and is still subject to the expected scan line height changes per the vertical scroll value. ==See also== CTIA/GTIA Horizontal blank interrupt Vertical blank interrupt ==References== ==External links== De Re Atari published by the Atari Program Exchange Mapping the Atari, Revised Edition by Ian Chadwick ANTIC chip data sheet scanned to PDF.

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