Atari XL User Manual

CHAPTER 14
ADVANCED GRAPHICS
This chapter deals with the way in which the XL
generates the various displays discussed in the last
three Chapters. It describes how the computer
controls the TV and how you can alter this
mechanism to produce yet more varied displays.
THE ANTIC AND GTIA CHIPS
The Atari uses two special chips to handle the
requirements of generating a display, called
ANTIC and GTIA. The ANTIC chip takes the data
concerning a display from display memory and
passes it to the GTIA chip in the correct form for
the display type currently selected.
The GTIA chip uses the data to control the TV and
so create the display. To understand how this
process works, you must understand some of the
principles used to generate TV pictures.
TV PICTURES
The pictures on a TV screen are created by an
electron beam which is directed at the phosphor
coated inner surface of the screen. Where this
beam strikes the screen, the phosphor glows. To
create a full screen picture, the electron beam scans
across the screen in rows, varying in intensity as it
goes. This variation in intensity is dictated by
information from the TV transmitter and produces
a corresponding variation in the intensity with
which the phosphor glows. When the electron beam
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Atari XL Specifications

General

Release Year	1983
CPU	MOS Technology 6502C
Graphics	ANTIC, GTIA
Sound	POKEY (4 channels)
Storage	Cassette tape
Ports	Cartridge
Operating System	Atari BASIC
CPU Speed	1.79 MHz
RAM	64 KB