Atari ANTIC

Connections of the 40-pin ANTIC chip

The Alphanumeric Television Interface Controller ( ANTIC ) is a microprocessor from the US manufacturer Atari that takes on various tasks, mainly in the area of ​​graphics generation. It was used in the Atari 400 , Atari 800 home computers , the models of the XL and XE series and in the Atari 5200 game console .

Working method

Like the 6502 main processor, the ANTIC can also access the entire main memory via direct memory access ( DMA ), for example to read out the program instructions and data intended for it. During these accesses the main processor is stopped at the same time, whereby the holding time can be up to 36 percent of the otherwise possible maximum CPU execution time (with up to 192 displayed raster lines) depending on the scope and type of image generation.

Although the ANTIC only has significantly less complex instructions than the 6502 microprocessor, it offers a wealth of possibilities for user-defined creation of the image content. The required display list instruction list with blank lines, jump and display commands has to be stored in the main memory by the operating system of the computer or by the user. With the aid of the display commands, one of the predefined text and point graphic levels can be selected for each line of the screen. These ANTIC display modes can be freely selected per line, which means that they can be mixed vertically as required.

The resolution of the text levels ranges from 20 to 40 characters per line with up to 30 lines. In the highest resolution graphics level, 320 × 240 pixels (letter word from the English Picture Cell , in German about a block of pixels ) are possible. However, with Atari computers with the NTSC screen standard, some of the upper and lower screen lines are not visible on the image device, which is why the graphics modes provided by the operating systems only use 192 raster lines.

In addition, the ANTIC enables when reaching or leaving certain screen positions, i. H. synchronous to the display , the execution of CPU subroutines through the display list interrupt , a non-maskable interrupt . In this way, line-dependent manipulations in particular can be carried out on the screen, including changing the colors, for example. The ANTIC also supports scrolling , i.e. H. the smooth fine shifting of the screen content.

After loading the image information, the ANTIC processes and transmits the data pixel by pixel to a second component, the CTIA or GTIA . This supplements other image components and generates the actual television output.

literature

• Julian Reschke, Andreas Wiethoff: The Atari professional book. Sybex-Verlag GmbH, Düsseldorf, 1986, ISBN 3-88745-605-X
• Eichler, Grohmann: Atari 600XL / 800XL Intern. Data Becker GmbH, 1984, ISBN 3-89011-053-3

Web links

• Detailed information on Atari's special modules (English)

Notes and individual references

1. ↑ Eichler, Grohmann: Atari Intern . 1st edition. Data Becker, 1984, p. 74 ff.