ANTIC
ANTIC is a 2D graphics chip using a display list.
The ANTIC (Alphanumeric Television Interface Controller) is a dedicated LSI ASIC chip that generates 2D computer graphics for television or computer displays. It was designed between 1977 and 1978 by Joe Decuir, Francois Michel, and Steve Smith, under the direction of Jay Miner, for the Atari 8-bit computers that launched in 1979. Atari, Inc. patented the chip in 1981. The same ANTIC hardware also appears in the 1982 Atari 5200 video game console, which shares most of its components with the 8-bit computer line.
For each video frame, ANTIC reads a set of instructions—called a display list—that defines the playfield (background graphics). It then sends a data stream to a companion chip, either the CTIA or GTIA, which adds color and overlays sprites (known at Atari as "Player/Missile graphics"). Each instruction in the display list corresponds to either blank scan lines or one of 14 graphics modes, applied to a horizontal band of the display. The height of each band varies by mode. The display list effectively builds the entire screen from a stack of these individual mode bands.
The display list also specifies the memory source for each row of data. For character modes, the base address of the character bitmaps is held in an on-chip register and can be changed. Instructions within the display list can enable horizontal and vertical fine scrolling, and can mark a scan line to trigger an interrupt. Such an interrupt allows arbitrary 6502 CPU code to run, typically to alter display settings mid-frame.
The chip uses direct memory access (DMA) to read the display list program. Its inherent hardware capabilities—excluding results from CPU-serviced interrupts or frequent register changes—include: 14 graphics modes (six character modes with four font/glyph rendering types, and eight bitmapped modes); outputting a variable number of blank scan lines; mixing playfield text and map modes onscreen; variable screen height up to vertical overscan; horizontal and vertical coarse scrolling; identifying sections of the display for horizontal or vertical fine scrolling; triggering a CPU-serviced display list interrupt at specific scan lines; and triggering a vertical blank interrupt at the end of the frame.
- Designers
- Joe Decuir, Francois Michel, Steve Smith
- Director
- Jay Miner
- Design period
- 1977–1978
- First used
- 1979 Atari 8-bit computers
- Patented
- 1981 by Atari, Inc.
- Also used in
- 1982 Atari 5200 video game console
- Part numbers
- C012296 (NTSC), C014887 (PAL/SECAM), C021697 (NTSC), C021698 (PAL/SECAM)
Lore & Background
Under the direction of Jay Miner, ANTIC 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, then delivers a data stream to the companion CTIA or GTIA chip which adds color and overlays sprites (called '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 instructions comprise a display list, 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. The Atari computer magazine Antic was named after the chip.
Reader's Guide
ANTIC's significance lies in its hardware capabilities that offload graphics processing from the CPU, using DMA to read a display list program. It provides 14 different graphics modes, including 6 character modes and 8 bitmapped modes, and supports mixing text and map modes onscreen. It enables variable screen height and width up to overscan, horizontal and vertical coarse and fine scrolling, and triggers CPU-serviced interrupts at specific scan lines (Display List Interrupt) and at the end of the frame (Vertical Blank Interrupt). ANTIC also performs DMA for CTIA/GTIA to produce Player/Missile graphics (sprites). Its non-fixed RAM allows graphics features to be located almost anywhere in the 16-bit memory address range. The chip is mapped to the $D4xx hex page in the Atari 8-bit computers and Atari 5200, providing 15 read/write registers. Operating system shadow registers in RAM store values written to hardware registers to avoid overwrite issues. Atari, Inc. intended to combine ANTIC and GTIA functions into a single chip (CGIA and KERI prototypes) to reduce production costs, but neither entered production.
Frequently Asked Questions
What is ANTIC?
ANTIC (Alphanumeric Television Interface Controller) is a dedicated LSI graphics chip that produces 2D computer graphics for television or monitor displays. It was built specifically for Atari's 8-bit home computers.
Who designed ANTIC?
Joe Decuir, Francois Michel, and Steve Smith designed the chip between 1977 and 1978, working under the direction of Jay Miner.
What systems used the ANTIC chip?
ANTIC first shipped in the 1979 Atari 8-bit computer line and later appeared in the 1982 Atari 5200 console, which shared most of its hardware with those computers.
How does ANTIC generate a display?
For every video frame, ANTIC reads a sequence of instructions called a display list, which tells it how to render the on-screen graphics. This display-list architecture is what defines it as a 2D graphics controller.
When was ANTIC patented?
Atari, Inc. filed a patent for the ANTIC chip in 1981, about two years after it first shipped in their home computers.
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