Editing Atari 400

{{Infobox computer
| name         = Atari 400
| image        = [[File:Atari-400-Comp.jpg|250px]]
| caption      = Atari 400 home computer (1979)
| manufacturer = Atari, Inc.
| type         = Home computer
| release date = November 1979
| discontinued = 1983
| price        = US$550 (1979)
| cpu          = MOS Technology 6502 @ 1.79 MHz (NTSC) / 1.77 MHz (PAL)
| memory       = 8 KB RAM (original), later models 16 KB or 48 KB RAM
| storage      = External cassette tape (410 Program Recorder), optional 810 5.25" floppy disk drive
| display      = 40×24 text, 320×192 pixels (max), 128 colours (NTSC: 256 hues x 128 luminances)
| sound        = POKEY: 4 channels, 8-bit, noise, random, keyboard scan
| dimensions   = 41 cm × 24 cm × 9 cm
| weight       = 3.2 kg
| os           = Atari BASIC (cartridge), Atari OS in ROM
| predecessor  = 
| successor    = [[Atari 800]]
| codename     = Candy
| model        = CX2624
| logo         = [[File:Atari 400 logo-04.svg|250px]]
}}

The '''Atari 400''' is an 8-bit home computer introduced by Atari, Inc. in November 1979. Designed as a more affordable and child-friendly sibling to the [[Atari 800]], the 400 featured a membrane keyboard and robust plastic case, targeting the home computing and educational markets.

== Architecture and Processor ==
At the heart of the Atari 400 is the '''MOS Technology 6502''' microprocessor, running at:
* '''1.79 MHz''' (NTSC systems)
* '''1.77 MHz''' (PAL systems)

The system architecture is built around custom Atari co-processors:
* '''ANTIC''' – programmable video interface controller, responsible for display list processing and graphics generation.
* '''CTIA/GTIA''' – handles colour, player/missile graphics (sprites), and video output.
* '''POKEY''' – manages sound generation, keyboard scanning, serial I/O, and random number generation.

This multi-chip design allowed the Atari 400 to deliver advanced graphics and sound capabilities for its time.

== Memory and Storage ==
The Atari 400 was originally shipped with '''8 KB RAM''' (expandable to 16 KB and later 48 KB via third-party upgrades). ROM contained the system OS and I/O routines. Application software and the Atari BASIC interpreter were supplied on plug-in cartridges.

Storage options included:
* '''410 Program Recorder''' – external cassette tape drive for program and data storage.
* '''810 floppy disk drive''' – optional 5.25" single-sided, single-density drive (via SIO port).

== Display and Graphics ==
Graphics capabilities were a major strength of the Atari 400, provided by the ANTIC and CTIA/GTIA chips:
* '''Text modes''': 40×24 and 20×24 characters
* '''Graphics modes''': up to 320×192 pixels (bitmap), with multiple colour and resolution options
* '''Colours''': Up to 128 (NTSC) or 104 (PAL) simultaneous colours via palette and luminance controls
* '''Sprites''': 4 player and 4 missile hardware sprites ("player/missile graphics")
* Smooth scrolling and fine control over display via programmable display lists

The system could output video via RF modulator (for TVs) or composite video (with modification).

== Sound Capabilities ==
Sound was generated by the '''POKEY''' chip, offering:
* '''4 independent audio channels'''
* 8-bit resolution, with selectable frequencies and noise generation
* Programmable audio control for effects and music
* Integrated keyboard scanning and random number generator

The POKEY chip enabled complex sound effects and music, making the Atari 400 popular for gaming.

== Input/Output and Expansion ==
The Atari 400 included the following I/O and expansion features:
* '''Cartridge slot''' – for games and software (Atari BASIC, educational titles, etc.)
* '''4 joystick ports''' – supporting Atari-compatible digital controllers
* '''SIO (Serial Input/Output) port''' – daisy-chainable connection for cassette, disk drives, printers, modems, and other peripherals
* '''RF output''' – for connection to standard television sets

Unlike the Atari 800, the 400 did not include user-accessible internal expansion slots and was limited to its factory RAM configuration (though third-party upgrades became available).

== PCB Schematics & Service Manual ==
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{| class="wikitable styled-table" style="width:75%; text-align:center;"
|+'''Atari 400 Main Boards'''
|-
! Logic Board !! Logic Board Schematic
|-
| [[File:Atari 400 mainboard and daughterboard.png|center|thumb|300x300px|Atari 400 Logic Board]]<br>
| [[File:Atari 400 800 Home Computer Schematics.pdf|alt=Atari 400 / 800 Schematics|center|thumb|Atari 400 / 800 Schematics]]<br>
|}

Official service manuals and schematics are available via the [[Atari 400 800 Field Service Manual June 82|Atari 400 / 800 Field Service Manual]]

== Gallery ==
<gallery mode="packed" heights="180">
File:Atari-400-Comp.jpg|Atari 400 front view
File:Atari 400 Interfaces.jpg|Atari 400 Interfaces
File:Atari 400 mainboard and daughterboard.png|Atari 400 logic board (main PCB)
File:Atari-400-Computer-Opened.jpg|Cartridge slot open
</gallery>

== Related Pages ==
* [[Atari 400 General Maintenance]]
* [[Atari 400 Troubleshooting Guide]]
* [[Atari 400 Keyboard Repair Guide]]
* [[Atari 400 Capacitor Replacement Guide]]

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[[Category:Atari Systems]]