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Ctia and gtia

The meaning of «ctia and gtia»

Color Television Interface Adaptor[1] (CTIA) and its successor Graphic Television Interface Adaptor[1] (GTIA) are custom chips used in the Atari 8-bit family of computers and in the Atari 5200 home video game console. In these systems, a CTIA or GTIA chip works together with ANTIC to produce the video display. ANTIC generates the playfield graphics (text and bitmap) while CTIA/GTIA provides the color for the playfield and adds overlay objects known as player/missile graphics (sprites). Under the direction of Jay Miner, the CTIA/GTIA chips were designed by George McLeod with technical assistance of Steve Smith.[2][3][4]

Color Television Interface Adaptor and Graphic Television Interface Adaptor are names of the chips as stated in the Atari field service manual.[1] Various publications named the chips differently, sometimes using the alternative spelling Adapter[5][6] or Graphics,[3] or claiming that the "C" in "CTIA" stands for Colleen/Candy[5] and "G" in "GTIA" is for George.[3][5][6][7]

Atari had built their first display driver chip, the Television Interface Adaptor but universally referred to as the TIA, as part of the Atari 2600 console.[8] The TIA display logically consisted of two primary sets of objects, the "players" and "missiles" that represented moving objects, and the "playfield" which represented the static background image on which the action took place. The chip used data in memory registers to produce digital signals that were converted in realtime via a digital-to-analog converter and RF modulator to produce a television display.

The conventional way to draw the playfield is to use a bitmap held in a frame buffer, in which each memory location in the frame buffer represents one or more locations on the screen. In the case of the 2600, which normally used a resolution of 160x192 pixels, a frame buffer would need to have at least 160x192/8 = 3840 bytes of memory. Built in an era where RAM was very expensive, the TIA could not afford this solution.

Instead, the system implemented a display system that used a single 20-bit memory register that could be copied or mirrored on the right half of the screen to make what was effectively a 40-bit display. Each location could be displayed in one of four colors, from a palette of 128 possible colors. The TIA also included several other display objects, the "players" and "missiles". These consisted of two 8-bit wide objects known as "players", a single 1-bit object known as the "ball", and two 1-bit "missiles". All of these objects could be moved to arbitrary horizontal locations via settings in other registers.

The key to the TIA system, and the 2600's low price, was that the system implemented only enough memory to draw a single line of the display, all of which held in registers. To draw an entire screen full of data, the user code would wait until the television display reached the right side of the screen and update the registers for the playfield and player/missiles to correctly reflect the next line on the display. This scheme drew the screen line-by-line from program code on the ROM cartridge, a technique known as "racing the beam".

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