Editing Atari 8-bit computers (section)

=== CTIA/GTIA ===

The [[CTIA and GTIA|Color Television Interface Adaptor]]<ref name="service-manual-name-2">{{cite book|title=Atari Home Computer Field Service Manual - 400/800|section=I. Theory of Operation|publisher=Atari, Inc.|url=http://www.digitpress.com/library/techdocs/Atari_400-800_Service_Manual.pdf|access-date=September 10, 2010|pages=1–10}}</ref> (CTIA) is the graphics chip originally used in the Atari 400 and 800. It is the successor to the [[Television Interface Adaptor|TIA]] chip of the 1977 Atari VCS. According to Joe Decuir, George McLeod designed the CTIA in 1977. It was replaced with the [[CTIA and GTIA|Graphic Television Interface Adaptor]]<ref name="service-manual-name-2"/> (GTIA) in later revisions of the 400 and 800 and all later 8-bit models. GTIA, also designed by McLeod, adds three new playfield graphics modes to ANTIC which enable more colors.{{sfn|Current|2023|loc=1.12) What are SALLY, ANTIC, CTIA/GTIA/FGTIA, POKEY, and FREDDIE?}}

The CTIA/GTIA receives Playfield graphics information from ANTIC and applies colors to the pixels from a 128 or 256 color palette depending on the color interpretation mode in effect. CTIA/GTIA controls Player/Missile Graphics ([[sprite (computer graphics)|sprites]]) including collision detection between players, missiles, and the playfield; display priority for objects; and color/luminance control of all displayed objects. CTIA/GTIA outputs separate digital luminance and chroma signals, which are mixed to form an analog composite video signal.

CTIA/GTIA reads the joystick triggers and the Option, Select and Start keys, and controls the keyboard speaker in the Atari 400 and 800. In later computer models the audio output for the keyboard speaker is mixed with the audio out for transmission to the TV/video monitor.