Atari 400
.jpg) | |
| Atari 400 home computer | |
| Specifications | |
|---|---|
| Manufacturer | Atari, Inc. |
| Type | Home computer |
| Released | November 1979 (first shipments)[1] |
| Discontinued | 1983 (production ended May 1983)[1] |
| Intro price | US$549.99 (1979 package with 8 KB)[1] |
| CPU | 6502B (SALLY on late units), 1.79 MHz NTSC / 1.77 MHz PAL[1] |
| Memory | 8 KB or 16 KB RAM; operating system in ROM |
| Storage | Cassette (410 Program Recorder) or 5.25" floppy disk drive over SIO; ROM cartridge |
| Display | 40 × 24 text, up to 320 × 192 pixels |
| Sound | POKEY: four audio channels |
| OS / Firmware | Atari Operating System in ROM; Atari BASIC on cartridge |
| Successor | Atari 600XL |
| Codename | Candy |
| Model no. | 400 |
The Atari 400 is an 8-bit home computer made by Atari, Inc. from 1979 alongside the larger Atari 800. The two machines share a processor, a custom chipset and an operating system. The 400 is the lower-cost model, with a flat membrane keyboard, one cartridge slot, no monitor output and no user-accessible memory slots.[1]
Atari's field service manual of June 1982 documents the 400 and the 800 together.[2]
History
[edit | edit source]The "Colleen" project produced two machines: the full "Colleen", released as the Atari 800, and the reduced "Candy", released as the 400. Atari showed both at the Winter CES in January 1979 and quoted US$500 for the 400. The first consumer units shipped in November 1979, 400s to Sears first; the launch package with 8 KB, BASIC cartridge, manuals, power supply and TV switch box listed at US$549.99.[1]
Atari later dropped the 8 KB model (May 1981) and cut the price of the 16 KB machine in steps, to US$199 in January 1983. Production of the 400 and 800 ended in May 1983, and the 400 and 800 were announced as discontinued when the 600XL and 800XL were introduced at the Summer CES in June 1983.[1] Early 400s have a CTIA video chip and most have the GTIA; late units use a revised CPU board with Atari's SALLY version of the 6502.[1]
Architecture
[edit | edit source]The 400 is built around a 6502 running at 1.79 MHz on NTSC machines.[2] The motherboard generates the 3.58 MHz master clock for the CPU board, the power-on reset for the CPU board and the peripherals, the drive for the keyboard click speaker, and the first stage of memory-map decoding, which splits the 64 KB address space into 8 KB blocks.[2]
| Location | Atari P/N | Device | Function |
|---|---|---|---|
| A303 (CPU card) | C014377 | 6502B | Microprocessor |
| A302 (CPU card) | C012296 | ANTIC | Display processor: reads a display list from memory, generates the playfield, controls bus access and DRAM refresh |
| A301 (CPU card) | C014805 (GTIA), earlier C012295 (CTIA) | GTIA or CTIA | Colour and luminance, player/missile graphics, collision detection |
| A101 (motherboard) | C012294 | POKEY | Keyboard scanning, serial I/O, four audio channels |
| A102 (motherboard) | C014795 or C014812 | 6520 PIA | Two 8-bit I/O ports for the controller jacks |
| A103, A104 (motherboard) | C014599, C012499 | 4 KB ROMs | Operating system |
| A105 (motherboard) | C012399 | 2 KB ROM | Operating system |
| A111 (motherboard) | C010816 | CD4050 | Hex buffer |
| Z101, Z102 (motherboard) | C014336 | 4051B | Keyboard scanning multiplexers |
| Z103 (motherboard) | C014361 | 74LS42 | Memory-map decoder |
Part numbers and locations are from Atari's 400 parts list; the functions are from the theory-of-operation section.[2] Atari's Upgrade Bulletin 1 (28 May 1982) replaces the CTIA C012295 at A301 with the GTIA C014805, which adds three graphics modes and runs CTIA software.[2]
The four controller jacks are J101–J104 and the cartridge socket is J108; the CPU and RAM cards plug into J109 (22/44-way) and J110 (28/56-way).[2]
Memory and storage
[edit | edit source]The 400 was built with 8 KB or 16 KB of RAM on a plug-in card, plus the operating system in ROM.[2] The 16 KB card (CA014802) carries eight dynamic RAMs at Z505–Z512.[2] Atari treated 16 KB as the finished machine; other companies found ways to expand it,[3] and Atari sold a 48 KB expansion kit for the 400, which needed some soldering, to dealers only.[1]
A program cartridge contains two 4 KB ROM chips.[2] Mass storage is external on the SIO serial bus: the 410 Program Recorder for cassettes, or an 810 or 1050 disk drive.
Display and sound
[edit | edit source]Video is produced by ANTIC with the CTIA or GTIA: text up to 40 columns by 24 rows, bitmap modes up to 320 × 192 pixels, four players and four missiles with collision detection, and programmable display lists. The composite video, luminance, chroma and modulator signals go from the motherboard to the power supply board, where the RF module produces the television signal. The 400 has no monitor jack; its only video output is RF, on channel 2 or 3 set by a switch at the back.[2]
POKEY provides four audio channels, each with its own frequency, noise and volume control. The same chip scans the keyboard and drives the SIO port.[2]
Input and output
[edit | edit source]- One cartridge slot under the top panel. A power interlock switch breaks power when the panel is opened to change a cartridge.[2]
- Four controller jacks (J101–J104) on the front. Port 4 is the only one on the 400 that supports a light pen or light gun.[1] The XL machines that replaced the 400 have two ports, because PORTB of the PIA, which served ports 3 and 4, was reused for operating-system and BASIC switching.[3]
- Peripheral (SIO) jack J202 on the right side, for daisy-chained disk drives, recorders, printers and modems.[2] SIO pin 12 carries +12 V on the 400 and 800.[1]
- RF output, with a channel 2/3 switch at the back.
- Power jack and power switch on the right side.[2]
Keyboard
[edit | edit source]The keyboard is a matrix of 57 normally open switches, scanned and encoded by POKEY through the two 4051 multiplexers on the motherboard. To the right of the keys are the power light and four console keys: SYSTEM RESET, OPTION, SELECT and START.[2] The keyboard assembly is Atari CA014031, replaced by CA017999.[2]
Power
[edit | edit source]The 400 does not take a DC supply. The external adaptor (Atari C014319) is a transformer that delivers 9 V AC to the console at the power jack J204. The power supply board inside the console rectifies and regulates that to three rails:[2]
| Rail | J201 pin | Source | Feeds |
|---|---|---|---|
| +5 V A | 5, 6 | Regulator A202 (drawn as a 7805, Atari C014348) with a 33 Ω 2 W resistor across it, R203 on the schematic and R202 in the parts list | Logic boards |
| +5 V B | 7 | +5 V A through L201 (1 µH), with C206 and C207 | Video circuitry |
| +12 V | 2 | Voltage doubler (CR204, CR205, C204, C205) into regulator A201 (78M12, Atari C014349) | Dynamic RAM; SIO pin 12 |
| −5 V | 18 | CR202, CR203, C201, C202, with 5.1 V zener CR201; the power LED CR210 is in this circuit | Dynamic RAM |
The bridge rectifier is CR206–CR209 and the main reservoir C209 (4700 µF). The power switch S203 and the interlock switch S202 are in series in the 9 V AC input.[2] The RF module (A203) is on the same board.
 | The regulated +5 V DC supplies sold for Atari XL and XE machines do not fit the 400 and must not be used on it. The 400 expects 9 V AC at the jack and has its own rectifier, regulators and filter capacitors.[2] |
Checking a machine
[edit | edit source]Atari's field procedure starts with three checks that need no test equipment:[2]
- Power-up test. With the adaptor and television connected and no cartridge fitted, switch on. The words ATARI COMPUTER - MEMO PAD should appear at the top left of the screen.
- Keyboard test. Press each key in turn, including combinations with CTRL, and check that each one appears.
- RAM and ROM test, with Atari's SALT II diagnostic cartridge.
The 400 and 800 have no built-in self test; the self-test program is an XL and XE feature.[2][3] The operating system revision can be read from BASIC with PRINT PEEK(65527): 221 is 400/800 Rev. A and 255 is Rev. B.[3] Revision A and B ROMs must not be mixed (Atari Tech Tip 2, 28 May 1982).[2]
Fault-finding is on the Atari 400 Troubleshooting Guide.
Schematics and service manual
[edit | edit source]| Logic board schematics | Field service manual |
|---|---|
| File:Atari 400 800 Home Computer Schematics.pdf | File:Atari 400 800 Field Service Manual June 82.pdf |
The manual is described on Atari 400 800 Field Service Manual June 82.
Related pages
[edit | edit source]- Atari 400 General Maintenance
- Atari 400 Troubleshooting Guide
- Atari 400 Capacitor Replacement Guide
- Atari 800
- Atari 600XL
References
[edit | edit source]- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 Michael D. Current (ed.), Atari 8-Bit Computers: Frequently Asked Questions, comp.sys.atari.8bit FAQ, last modified 29 November 2009, section 1.2 "What is the Atari 400?", the performance specifications, and the history timeline for 1978–1983. faqs.org. Community reference, used for dates, prices, codenames, model variants and clock rates.
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 2.14 2.15 2.16 2.17 2.18 2.19 2.20 2.21 Atari, Inc., ATARI Home Computer Field Service Manual 400/800, June 1982. Section 1 (theory of operation, pp. 1-1 to 1-26), Section 2 (silkscreens and schematics; 400 power supply schematic, Figure 2-4, p. 2-7), Section 3 (testing with and without the SALT II cartridge), Section 5 (400 diagnostic flowcharts), Section 6 (symptom checklist) and Section 9 (400 parts list, pp. 9-2 to 9-6). Hosted here as Atari 400 800 Field Service Manual June 82 (PDF).
- ↑ 3.0 3.1 3.2 3.3 Robert DeWitt, "Inside Atari: Evolution of the XL Computers", Antic Vol. 3 No. 2 (June 1984), atarimagazines.com. Source for the 400 being complete at 16 KB, the loss of joystick ports 3 and 4 on the XL machines, the single 5 V supply of the 600XL/800XL, and the PEEK(65527) operating-system values.