George's Television Interface Adapter

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George's Television Interface Adapter (GTIA) is the successor to the CTIA chip used in the Atari 8-bit computers. The GTIA chip was also used in the Atari 5200. George McLeod designed the chip.

The GTIA chip added the following capabilities to the existing CTIA:

256 colors instead of 128. This was done by increasing the valid luminance values from 8 to 16.
3 additional graphics modes. All 3 modes are 80x192 pixels, with the difference being in the colors allowed -- one mode allows for 16 shades of a single hue, one allows for 16 hues with a single shade/luminance value, and the last one allows for 9 colors of any hue/luminance.

GTIA also generates keyboard clicks.

In addition, due to differences in how the CTIA and the GTIA interface with the television, programs that depend on color artifacts will display differently.

By 1981, all Atari computers were equipped with the GTIA chip.

See also: ANTIC, CTIA

[edit] Versions

by part number

C014805 — NTSC. North America NTSC.
C014889 — PAL. European PAL.
C020120 — FGTIA. French SECAM video.
C020577 — CGIA. Combined ANTIC and GTIA.

[edit] Bugs

Atari XE computers made for the Eastern European market were built in China. Many if not all have a buggy PAL GTIA chip. The luma values in Gr.9 and higher are at fault, appearing as stripes. Only solution is to replace the chip.