Editing Atari 7800 (section)

==Technical specifications==
[[File:Atari-7800-Motherboard-01.jpg|thumb|Motherboard of an American 7800 with the RF shielding removed]]
[[File:Atari-7800-Motherboard-Euro-wRGB-FL.jpg|thumb|European motherboard modified by Atari to output RGB through a SCART connector]]
* CPU: [[SALLY (microprocessor)|Atari SALLY]] (custom variant of the [[MOS Technology 6502|6502]])
** 1.79&nbsp;MHz, which drops to 1.19&nbsp;MHz when the [[Television Interface Adaptor]] or ([[MOS Technology 6532|6532 RAM-I/O-Timer]]) chips are accessed
** Unlike a standard 6502, ''SALLY'' can be halted in a known state with a single pin to let other devices control the bus.
** Sometimes referred to by Atari as "6502C", but not the same as the official [[MOS Technology]] 6502C.<ref name='am_sally'>{{cite web|url=http://www.atarimania.com/faq-atari-400-800-xl-xe-what-are-sally-antic-ctia-gtia-fgtia-pokey-and-freddie_14.html|title=FAQ 400 800 XL XE : What are SALLY, ANTIC, CTIA/GTIA/FGTIA, POKEY, and FREDDIE?|quote=named SALLY by Atari engineers, but [support documents call it] "6502 (Modified)", "6502 Modified", "Custom 6502", or "6502C". [..] SALLY 6502 chips are never marked "6502C" but, other than the UMC UM6502I, always [marked] C014806. [..] [Other] chips marked "6502C" [..] are NOT the Atari "6502C" but [standard 6502] certified for 4MHz|archiveurl=https://web.archive.org/web/20200719024918/http://www.atarimania.com/faq-atari-400-800-xl-xe-what-are-sally-antic-ctia-gtia-fgtia-pokey-and-freddie_14.html|archivedate=19 July 2020}}</ref>
* [[Random-access memory|RAM]]: 4 KB<ref name="EGM62"/> (2 6116 2Kx8 RAM [[integrated circuit|ICs]])
* [[Read-only memory|ROM]]: built in 4 KB [[BIOS]] ROM, 48 KB Cartridge ROM space without [[bank switching]]
* Graphics: MARIA custom chip
** Resolution: 160×240 (160×288 [[PAL region|PAL]]) or 320×240 (320×288 PAL)
** Color palette: 256<ref name="EGM62"/> (16 [[hue]]s * 16 [[Luma (video)|luma]]), different graphics modes restricted the number of usable colors and the number of colors per sprite
** [[Direct memory access|Direct Memory Access]] (DMA)
** Graphics clock: 7.15&nbsp;MHz<ref>{{Cite web|url=http://www.computinghistory.org.uk/det/15473/Atari-7800/|title=Atari 7800 - Game Console - Computing History|website=www.computinghistory.org.uk|access-date=2020-02-19}}</ref><ref name=maria>{{cite web |archive-url=https://web.archive.org/web/20101207034523/http://www.atarimuseum.com/ahs_archives/archives/pdf/videogames/7800/gcc1702b_maria_specs.pdf |archive-date=7 December 2010 |url=http://www.atarimuseum.com/ahs_archives/archives/pdf/videogames/7800/gcc1702b_maria_specs.pdf |title=GCC1702B "Maria" Chip}}</ref>
** [[Framebuffer|Line buffer]]: 200 bytes ([[Multiple buffering#Double buffering in computer graphics|double buffering]]), 160 [[Texel (graphics)|sprite pixels]] per [[Scan line|scanline]],<ref name=maria/> up to 30 [[Sprite (computer graphics)|sprites]] per scanline (without background),<ref name="vs7800" /> up to 100 sprites on screen<ref>{{cite web|url=http://www.ataritimes.com/index.php?ArticleIDX%3D632 |title=Atari 7800 vs. Nintendo NES |access-date=2014-09-29 |url-status=dead |archive-url=https://web.archive.org/web/20140628043258/http://ataritimes.com/index.php?ArticleIDX=632 |archive-date=2014-06-28 }}</ref><ref>{{Cite web|url=http://www.atarimuseum.com/videogames/consoles/7800/7800.html|archive-url = https://web.archive.org/web/20030624192139/http://www.atarimuseum.com/videogames/consoles/7800/7800.html|archive-date = 2003-06-24|title = The Atari 7800 ProSystem}}</ref>
** [[Sprite (computer graphics)|Sprite]]/zone sizes: 4<ref name=programming>{{cite web |url=http://sites.google.com/site/atari7800wiki/graphics-programming |title=Graphics Programming |website=Atari 7800 Progamming}}</ref> to 160<ref name=maria/> width, height of 4,<ref name=programming/> 8 or 16<ref name=guide/> pixels
** Colors per sprite: 1 to 12 (1 to 8 visible colors, 1 to 4 transparency bits)<ref name=guide>{{cite web| url=http://atarihq.com/danb/files/7800%20Software%20Guide.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://atarihq.com/danb/files/7800%20Software%20Guide.pdf |archive-date=2022-10-09 |url-status=live |title=7800 Software Guide}}</ref>
* I/O: Joystick and console switch IO handled by [[MOS Technology 6532|6532 RIOT]] and TIA
* Ports
**2 joystick ports
**cartridge port
**expansion connector
**power in
**[[RF modulator|RF]] output
* Sound: [[Television Interface Adaptor|TIA]] as used in the 2600 for video and sound. In 7800 mode it is only used for sound.
** At least two games include a [[POKEY]] [[sound chip]] for improved audio.<ref>{{Cite book|url=https://books.google.com/books?id=bGEbLt1C168C&pg=PA201|title=Hardware Hacking: Have Fun while Voiding your Warranty|last1=Grand|first1=Joe|last2=Mitnick|first2=Kevin D.|last3=Russell|first3=Ryan|date=2004-01-29|publisher=Elsevier|isbn=978-0-08-047825-8|pages=201|language=en}}</ref><ref>{{Cite web|url=http://visual6502.org/images/pages/Atari_C012294_POKEY_die_shots.html|title=Atari C012294 POKEY|website=visual6502.org|access-date=2019-12-05}}</ref>

=== Graphics ===
Graphics are generated by the custom MARIA chip, which uses an approach common in contemporary arcade [[Arcade system board|system boards]]<ref name=guide/> and is  different from other [[Second generation of video game consoles|second]] and [[Third generation of video game consoles|third generation]] consoles. Instead of a limited number of hardware sprites, MARIA treats everything as a sprite described in a series of [[display list]]s. Each display list contains pointers to graphics data and color and positioning information.

MARIA supports a palette of 256 colors and graphics modes which are either 160 pixels wide or 320 pixels wide. While the 320 pixel modes theoretically enable the 7800 to create games at higher resolution than the 256 pixel wide graphics found in the [[Nintendo Entertainment System]] and [[Master System]], the processing demands of MARIA result in most games using the 160 pixel mode.{{citation needed|date=March 2014}}

Each sprite can have from 1 to 12 colors, with 3 colors plus transparency being the most common. In this format, the sprite references one of 8 palettes, where each palette holds 3 colors. The background (visible when not covered by other objects) can also be assigned a color. In total, 25 colors can appear on a [[scan line]].<ref name=3600sg/>

The graphics resolution, color palettes, and background color can be adjusted between scan lines.<ref name=3600sg>{{cite web |title=Atari 3600 Software Guide |url=http://www.atarimuseum.com/ahs_archives/archives/pdf/videogames/7800/3600_software_guide.pdf |archive-url=https://web.archive.org/web/20101207033819/http://www.atarimuseum.com/ahs_archives/archives/pdf/videogames/7800/3600_software_guide.pdf |archive-date=2010-12-07 }}</ref>

=== Sound ===
The 7800 uses the TIA chip for two channel audio, the same chip used in the 1977 Atari VCS, and the sound is of the same quality as that system. To compensate, GCC's engineers allowed games to include a [[POKEY|POKEY audio chip]] in the cartridge. Only ''[[Ballblazer]]'' and ''[[Commando (video game)|Commando]]'' do this.

GCC planned to make a low-cost, high performance sound chip, GUMBY, which could also be placed in 7800 cartridges to enhance its sound capabilities further.<ref>{{Cite web |title=The 7800 Minnie sound chip - 8BitDev.org - Atari 7800 Development Wiki |url=https://7800.8bitdev.org/index.php/The_7800_Minnie_sound_chip |access-date=2024-03-02 |website=7800.8bitdev.org}}</ref> This project was cancelled when Atari was sold to Jack Tramiel.

=== Digitally signed cartridges ===
Following the large number of low quality, third party games for the Atari 2600, Atari required that cartridges for the 7800 be digitally signed. When a cartridge is inserted into the system, the BIOS generates a signature of the cartridge ROM and compares it to the one stored on the cartridge. If they match, the console operates in 7800 mode, granting the game access to MARIA and other features, otherwise the console operates as a 2600. This digital signature code is not present in PAL 7800s, which use various [[heuristic]]s to detect 2600 cartridges, due to export restrictions.

=== Backward compatibility ===
The 7800's compatibility with the Atari 2600 is made possible by including many of the same chips used in the 2600. When playing an Atari 2600 game, the 7800 uses a Television Interface Adaptor chip to generate graphics and sound. The processor is slowed to 1.19&nbsp;MHz, to mirror the performance of the 2600's [[MOS 6507|6507]] chip. RAM is limited to 128 bytes and cartridge data is accessed in 4K blocks.

When in 7800 mode (signified by the appearance of the full-screen Atari logo), the graphics are generated entirely by the MARIA [[graphics processing unit]]. All system RAM is available and cartridge data is accessed in larger 48K blocks. The system's SALLY 6502 runs at its normal 1.79&nbsp;MHz. The 2600 chips are used to generate sound and to provide the interfaces to the controllers and console switches.

===System revisions===
{{more sources|section|date=January 2024}}
*Initial version: two joystick ports on lower front panel. Side expansion port for upgrades and add-ons. Bundled with two CX24 Pro-Line joysticks, AC adapter, switchbox, [[RCA connector|RCA connecting cable]], and ''[[Pole Position II]]'' cartridge.
*Second revision: Slightly revised [[motherboard]]. Expansion port connector removed<ref name="archive.org">{{cite web | url=https://archive.org/details/atari_7800_library?tab=about | title=Console Living Room: Atari 7800 : Free Software : Free Download, Borrow and Streaming : Internet Archive }}</ref> from motherboard but is still etched. Shell has indentation of where expansion port was to be.
*Third revision: Same as above but with only a small blemish on the shell where the expansion port was.<ref>{{Cite web |title=Atari 7800 Pro System |url=https://www.ataricompendium.com/game_library/easter_eggs/7800/78prosystem.html |access-date=2023-04-14 |website=www.ataricompendium.com}}</ref>