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{{Infobox computer
{{Infobox computer
| name           = Atari 520ST
| name = Atari 520ST
| image         = [[File:Atari 520ST.jpg]]
| image = [[File:Atari520ST.jpg|250px]]
| manufacturer   = Atari Corporation
| manufacturer = Atari Corporation
| type           = Home computer
| type = Home computer / personal computer
| caption       = 520ST with external SF354 floppy drive and SC1224 color monitor
| caption = Early “short-case” 520ST with external PSU and external SF354 floppy drive
| release date   = {{Start date|1985|06}} <!-- limited release began June 1985; broadly available July 1985 -->
| release date = {{Start date|1985|06}}<ref>{{cite web |url=https://www.atarimagazines.com/compute/issue59/next_generation.php |title=The Next Generation: New Computers at the Winter Consumer Electronics Show |publisher=Compute! |date=1985-01 |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://en.wikipedia.org/wiki/Atari_ST |title=Atari ST |publisher=Wikipedia |date=2025-08-11 |access-date=2025-08-13}}</ref>
| discontinued   = 1986 <!-- superseded in production by 520STF/520STM; ST line discontinued 1993 -->
| discontinued = 1986–1987 (superseded in production by STF/STM variants; ST family continued to 1993)<ref>{{cite web |url=https://www.atarimagazines.com/compute/issue71/electronics_show.php |title=A Turning Point for Atari? Report from the Winter CES |publisher=Compute! |date=1986-02 |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://en.wikipedia.org/wiki/Atari_ST |title=Atari ST |publisher=Wikipedia |date=2025-08-11 |access-date=2025-08-13}}</ref>
| price         = US$799 bundle (520ST + SF354 + SM124 mono), US$999 (520ST + SF354 + SC1224 RGB) at U.S. launch (Oct. 1985).<ref>{{cite web |url=https://www.atarimagazines.com/compute/issue65/520st.php |title=Atari 520ST: A Hands-On Report |author=Tom R. Halfhill |publisher=Compute! |date=1985-10 |access-date=2025-08-13}}</ref>
| price = US$599 (CPU only, announced Jan 1985); US$699 mono bundle / US$899 color bundle (Jan 1986 SRP)<ref>{{cite web |url=https://www.atarimagazines.com/compute/issue59/next_generation.php |title=The Next Generation: New Computers at the Winter CES |publisher=Compute! |date=1985-01 |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://www.atarimagazines.com/compute/issue71/electronics_show.php |title=A Turning Point for Atari? CES 1986 price reductions |publisher=Compute! |date=1986-02 |access-date=2025-08-13}}</ref>
| cpu           = Motorola MC68000P8 @ 8 MHz (64‑pin DIP; some later boards MC68000FN8 PLCC)<ref>{{cite web |url=https://en.wikipedia.org/wiki/Atari_ST |title=Atari ST |publisher=Wikipedia |date=2025-08-11 |access-date=2025-08-13}}</ref>
| cpu = Motorola MC68000P8/MC68000FN8 @ 8.00 MHz<ref>{{cite web |url=https://www.alldatasheet.net/datasheet-pdf/pdf/135463/MOTOROLA/MC68000P8.html |title=MC68000P8 8 MHz Datasheet |publisher=Motorola (via AllDataSheet) |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://www.datasheets360.com/part/detail/mc68000fn8/-3094971039532773301/ |title=MC68000FN8 Datasheet summary |publisher=Datasheets360 |access-date=2025-08-13}}</ref>
| memory         = 512 KB RAM standard (DRAM, 16×256‑Kbit); commonly expanded to 1 MB; third‑party upgrades up to 4 MB.<ref>{{cite web |url=https://en.wikipedia.org/wiki/Atari_ST |title=Atari ST |publisher=Wikipedia |date=2025-08-11 |access-date=2025-08-13}}</ref>
| memory = 512 KB RAM standard; expandable to 1–4 MB via aftermarket DRAM/SIMM upgrades<ref>{{cite web |url=https://forums.atariage.com/topic/337575-520st-ram-upgrade-question/page/2/ |title=520ST RAM upgrade discussion (C070243 board) |publisher=AtariAge Forums |date=2022-09-14 |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://www.pcbway.com/project/shareproject/STRAM_4MB_Atari_520ST_M_Expansion_692e0348.html |title=STRAM 4MB Atari 520ST(M) Expansion |publisher=PCBWay community |date=2023-06-07 |access-date=2025-08-13}}</ref>
| storage       = External 3.5″ floppy (SF354 single‑sided 360 KB; later SF314 double‑sided 720 KB), ACSI (DB‑19) external hard disks (e.g., SH204), ROM cartridge slot (128 KB).<ref>{{cite web |url=https://archive.org/download/Atari_520ST_Owners_Manual_Rev._B_1985/Atari_520ST_Owners_Manual_Rev._B_1985.pdf |title=Atari 520ST Owner's Manual (Rev. B) |publisher=Atari Corporation |date=1985 |access-date=2025-08-13}}</ref>
| storage = External 3.5-inch SF354 SSDD 360 KB (standard); optional SF314 DSDD 720 KB; external ACSI hard disks (SH/MegaFile series)<ref>{{cite web |url=https://www.atarimagazines.com/v4n4/interiors.php |title=Interiors: Opening up the 520ST (ports overview) |publisher=Antic |date=1985-08 |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://info-coach.fr/atari/hardware/interfaces.php |title=Atari ST Interfaces / Connectors / Cables Information |publisher=info-coach.fr |access-date=2025-08-13}}</ref>
| display       = Low 320×200 (16 colors), Medium 640×200 (4 colors), High 640×400 (mono); 50/60 Hz color, 71.2 Hz mono.<ref>{{cite web |url=https://temlib.org/AtariForumWiki/index.php/Flat_Panel_Displays |title=The various Atari ST display modes |publisher=AtariForumWiki |access-date=2025-08-13}}</ref>
| display = 13‑pin DIN analog RGB and mono; 320×200 (16 colors), 640×200 (4 colors) at 50/60 Hz; 640×400 mono at ~71.2 Hz (SM124)<ref>{{cite web |url=https://temlib.org/AtariForumWiki/index.php/Flat_Panel_Displays |title=The various Atari ST display modes |publisher=AtariForumWiki |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://www.oldcomputers.it/parts/atari/1040STF/docs/connettore_monitor_st.htm |title=Atari ST monitor output and levels |publisher=oldcomputers.it |access-date=2025-08-13}}</ref>
| sound         = Yamaha YM2149F PSG, 3 tone voices + 1 noise source, programmable envelopes; mono output via monitor connector pin 1.<ref>{{cite web |url=https://en.wikipedia.org/wiki/Atari_ST |title=Atari ST |publisher=Wikipedia |date=2025-08-11 |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://info-coach.fr/atari/hardware/interfaces.php |title=Atari ST Interfaces / Connectors / Cables |author=Jean-Louis Guérin |publisher=info-coach.fr |access-date=2025-08-13}}</ref>
| sound = Yamaha YM2149F 3‑voice PSG (square/noise, 5‑bit envelope); mono line out on monitor port; MIDI In/Out<ref>{{cite web |url=https://en.wikipedia.org/wiki/General_Instrument_AY-3-8910 |title=General Instrument AY‑3‑8910 (Yamaha YM2149F variant) |publisher=Wikipedia |date=2025-08-13 |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://temlib.org/AtariForumWiki/index.php/Yamaha_YM2149_Manual |title=Yamaha YM2149 Manual |publisher=AtariForumWiki |access-date=2025-08-13}}</ref>
| dimensions     = 47.6 × 24.1 × 7.0 cm (18.75 × 9.5 × 2.75 in)<ref>{{cite web |url=https://americanhistory.si.edu/collections/object/nmah_1330999 |title=Atari 520ST Microcomputer |publisher=Smithsonian National Museum of American History |access-date=2025-08-13}}</ref>
| dimensions = 70 mm × 476 mm × 241 mm (2.75 × 18.75 × 9.5 in)<ref>{{cite web |url=https://americanhistory.si.edu/collections/object/nmah_1330999 |title=Atari 520ST Microcomputer (object record, measurements) |publisher=Smithsonian NMAH |access-date=2025-08-13}}</ref>
| weight         = ≈4.3 kg (9.5 lb) (unit without external PSU).<ref>{{cite web |url=https://myoldcomputers.com/museum/computers/atari_520st.htm |title=Atari 520ST |publisher=My Old Computers Museum |access-date=2025-08-13}}</ref>
| weight = ≈4.3 kg (9 lb 7 oz)<ref>{{cite web |url=https://myoldcomputers.com/museum/computers/atari_520st.htm |title=Atari 520ST specifications (dimensions/weight) |publisher=My Old Computers |access-date=2025-08-13}}</ref>
| os             = Atari TOS with GEM. Early 520ST units booted TOS from floppy (16 KB boot ROM); shortly after launch, TOS 1.00 shipped in 192 KB ROM (2‑ or 6‑ROM sets).<ref>{{cite web |url=https://archive.org/download/Atari_520ST_Owners_Manual_Rev._B_1985/Atari_520ST_Owners_Manual_Rev._B_1985.pdf |title=Atari 520ST Owner's Manual (Rev. B) |publisher=Atari Corporation |date=1985 |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://en.wikipedia.org/wiki/Atari_TOS |title=Atari TOS |publisher=Wikipedia |date=2024-12-01 |access-date=2025-08-13}}</ref>
| os = Atari TOS with Digital Research GEM; early units boot TOS from disk via small boot ROM, later 192 KB ROM‑TOS<ref>{{cite web |url=https://mikrosk.github.io/doitarchive/doit_st/0f0601.htm |title=TOS ROM sizes and configurations |publisher=DOIT_ST archive |access-date=2025-08-13}}</ref>
| predecessor   = [[Atari 8-bit family]]
| predecessor = [[Atari 8-bit family]]
| successor     = [[Atari 520STF]] / [[Atari 1040STF]]
| successor = [[Atari 1040ST]]
}}
}}


The Atari 520ST is Atari Corporation’s first 16/32‑bit ST‑series model, announced January 1985 and shipped in quantity mid‑1985. It pairs a Motorola 68000 at 8 MHz with the GEM desktop on TOS, integrated MIDI ports, and a cost‑effective graphics subsystem. Early North American bundles were priced at US$799 (mono) and US$999 (color).<ref>{{cite web |url=https://www.atarimagazines.com/compute/issue65/520st.php |title=Atari 520ST: A Hands‑On Report |author=Tom R. Halfhill |publisher=Compute! |date=1985-10 |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://en.wikipedia.org/wiki/Atari_ST |title=Atari ST |publisher=Wikipedia |date=2025-08-11 |access-date=2025-08-13}}</ref>
The Atari 520ST is the first widely released model of Atari’s 16/32‑bit ST family, built around the Motorola 68000 at 8 MHz with 512 KB RAM and a rich set of built‑in interfaces (notably MIDI). It debuted in 1985 with low bundled prices and a GEM desktop, competing directly with the Macintosh and Commodore Amiga.<ref>{{cite web |url=https://www.atarimagazines.com/compute/issue59/next_generation.php |title=The Next Generation: New Computers at the Winter CES |publisher=Compute! |date=1985-01 |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://www.atarimagazines.com/compute/issue71/electronics_show.php |title=CES 1986: 1040ST introduction and 520ST price changes |publisher=Compute! |date=1986-02 |access-date=2025-08-13}}</ref>


== Architecture and Processor ==
== Architecture and Processor ==
At its core, the 520ST uses a 16/32‑bit Motorola 68000:
Exact CPU and core architecture
* Exact CPU: Motorola MC68000P8 (DIP‑64) on early boards; some later STf/STfm use MC68000FN8 (PLCC‑68). Clock: 8.00 MHz (all regions).<ref>{{cite web |url=https://en.wikipedia.org/wiki/Atari_ST |title=Atari ST |publisher=Wikipedia |date=2025-08-11 |access-date=2025-08-13}}</ref>
* CPU: Motorola MC68000 (DIP‑64 MC68000P8 on early boards; later boards sometimes PLCC‑68 MC68000FN8), nominal 8.00 MHz.<ref>{{cite web |url=https://www.alldatasheet.net/datasheet-pdf/pdf/135463/MOTOROLA/MC68000P8.html |title=MC68000P8 8 MHz Datasheet |publisher=Motorola |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://www.datasheets360.com/part/detail/mc68000fn8/-3094971039532773301/ |title=MC68000FN8 8 MHz summary |publisher=Datasheets360 |access-date=2025-08-13}}</ref>
* Bus: 24‑bit address bus (16 MB address space), 16‑bit data bus; unified memory architecture with video DMA contention from the Shifter.<ref>{{cite web |url=https://temlib.org/AtariForumWiki/index.php/Flat_Panel_Displays |title=The various Atari ST display modes |publisher=AtariForumWiki |access-date=2025-08-13}}</ref>
* Architecture: 16/32‑bit 68000 core (32‑bit registers/ALU with 16‑bit external data bus; 24‑bit address bus for 16 MB address space).<ref>{{cite web |url=https://en.wikipedia.org/wiki/Atari_ST |title=Atari ST |publisher=Wikipedia |date=2025-08-11 |access-date=2025-08-13}}</ref>
* Major custom chips (exact part numbers as used on 520/1040ST family):
* System bus: 24 address lines, 16 data lines; unified memory (video fetches contend with CPU). Video DMA is performed by the Shifter reading DRAM under GLUE/MMU timing; the separate Atari “DMA” IC arbitrates ACSI/floppy transfers.<ref>{{cite web |url=https://temlib.org/AtariForumWiki/index.php/Atari_ST/STe/MSTe/TT/F030_Hardware_Register_Listing |title=Atari ST hardware register listing and memory map |publisher=AtariForumWiki |access-date=2025-08-13}}</ref>
** Shifter (video): C025914‑38/‑38A; also seen as CO70713/I10356 on some boards.<ref>{{cite web |url=https://mikrosk.github.io/doitarchive/doit_st/0303.htm |title=DOIT ST: Parts list (ST custom ICs) |publisher=DOIT_ST archive |access-date=2025-08-13}}</ref>
* Region timings: CPU runs at 8.00 MHz in all regions; display vertical refresh differs (50.05 Hz PAL, 60.04 Hz NTSC, mono ~71.5 Hz), derived from ~32.084988 MHz master clock on color modes.<ref>{{cite web |url=https://www.atari-forum.com/viewtopic.php?t=32842 |title=ST/STE video frequencies derivation |publisher=Atari‑Forum |date=2017-12-24 |access-date=2025-08-13}}</ref>
** GLUE (bus/logic/timing): C025915‑38A; also CO70714/I10355.<ref>{{cite web |url=https://mikrosk.github.io/doitarchive/doit_st/0303.htm |title=DOIT ST: Parts list (ST custom ICs) |publisher=DOIT_ST archive |access-date=2025-08-13}}</ref>
 
** MMU (DRAM controller): C025912‑38; later C100109/I10353.<ref>{{cite web |url=https://mikrosk.github.io/doitarchive/doit_st/0303.htm |title=DOIT ST: Parts list (ST custom ICs) |publisher=DOIT_ST archive |access-date=2025-08-13}}</ref>
Major custom and support ICs (typical 520ST/520STM/early STF family)
** DMA (ACSI/floppy DMA): C025913‑38 (Atari DMA controller).<ref>{{cite web |url=https://forums1128.rssing.com/chan-4289726/all_p480.html |title=Atari custom IC list (forum sale; part numbers collated) |publisher=RSSing (AtariAge content mirror) |access-date=2025-08-13}}</ref>
* Shifter (video DMA/serializer): Atari C025914‑38/‑38A; also seen as CO70713/I10356 on some boards.<ref>{{cite web |url=https://forums.atariage.com/topic/247569-huge-list-of-new-original-atari-custom-ic-chips-transistors-etc/ |title=Atari custom IC part numbers list (community collation) |publisher=AtariAge Forums |date=2016-01-05 |access-date=2025-08-13}}</ref>
** MFP (interrupts/timers/serial): Motorola MC68901.<ref>{{cite web |url=https://www.bighole.nl/pub/mirror/homepage.ntlworld.com/kryten_droid/Atari/ST/spg/st_prog_guide_1.htm |title=Concise Atari ST 68000 Programmer's Reference Guide – MC68901 MFP |publisher=bighole.nl mirror |access-date=2025-08-13}}</ref>
* GLUE (bus/timing/GLUe logic): Atari C025915‑38A (and SMD successors).<ref>{{cite web |url=https://forums.atariage.com/topic/247569-huge-list-of-new-original-atari-custom-ic-chips-transistors-etc/ |title=Atari custom IC part numbers list |publisher=AtariAge Forums |access-date=2025-08-13}}</ref>
** ACIA (keyboard and MIDI UARTs): 2× Motorola MC6850.<ref>{{cite web |url=https://www.atarimagazines.com/compute/issue73/st_hints_tips.php |title=ST Hints & Tips (IKBD and ACIA) |publisher=Compute! |date=1986 |access-date=2025-08-13}}</ref>
* MMU (DRAM controller/multiplexer): Atari C025912‑38; later C100109 on later boards.<ref>{{cite web |url=https://forums.atariage.com/topic/247569-huge-list-of-new-original-atari-custom-ic-chips-transistors-etc/ |title=Atari custom IC list |publisher=AtariAge Forums |access-date=2025-08-13}}</ref>
** Floppy controller: Western Digital WD1772 (commonly WD1772‑00‑02; later ‑02‑02 parts tolerate 16 MHz for HD mods).<ref>{{cite web |url=https://www.exxosforum.co.uk/atari/store2/0268.html |title=WD1772 00‑02 floppy controller |publisher=exxosforum store |access-date=2025-08-13}}</ref>
* DMA controller (ACSI/floppy DMA): Atari C025913‑38.<ref>{{cite web |url=https://mikrosk.github.io/doitarchive/doit_st/0904.htm |title=DOIT: DMA and ROM discussion with WD1772 photo |publisher=DOIT_ST archive |access-date=2025-08-13}}</ref>
* Region differences: CPU frequency remains 8.00 MHz worldwide; video refresh differs by region (50 Hz PAL vs 60 Hz NTSC; mono at ~71.2 Hz).<ref>{{cite web |url=https://temlib.org/AtariForumWiki/index.php/Flat_Panel_Displays |title=The various Atari ST display modes |publisher=AtariForumWiki |access-date=2025-08-13}}</ref>
* Interrupt/timers/UART: Motorola MC68901 MFP (system timers, interrupt controller, 200 Hz tick, handshake lines).<ref>{{cite web |url=https://www.bighole.nl/pub/mirror/homepage.ntlworld.com/kryten_droid/Atari/ST/spg/st_prog_guide_1.htm |title=Concise Atari ST Programmer’s Reference – MC68901 MFP |publisher=bighole.nl mirror |access-date=2025-08-13}}</ref>
* ACIAs: 2× Motorola MC6850 ACIA (keyboard/IKBD and MIDI), clocked at 500 kHz for MIDI 31.25 kbaud (÷16).<ref>{{cite web |url=https://www.muzines.co.uk/articles/atari-520st/9092 |title=Atari 520ST (MIDI hardware notes) |publisher=Electronics & Music Maker |date=1985-07 |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://www.bighole.nl/pub/mirror/homepage.ntlworld.com/kryten_droid/Atari/ST/spg/st_prog_guide_2.htm |title=Concise Atari ST Programmer’s Reference – MIDI/IKBD ACIAs |publisher=bighole.nl mirror |access-date=2025-08-13}}</ref>
* Floppy controller: Western Digital WD1772, commonly WD1772‑00‑02 or ‑02‑02; later chips tolerate 16 MHz for HD‑floppy mods.<ref>{{cite web |url=https://mikrosk.github.io/doitarchive/doit_st/0b03.htm |title=HD Disk ST (WD1772 02‑02, 16 MHz HD mods) |publisher=DOIT_ST archive |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://exxosforum.co.uk/atari/last/floppy/index.htm |title=The LaST upgrade – Atari 1.44 MB floppy mod notes |publisher=exxosforum |access-date=2025-08-13}}</ref>
* PSG audio + parallel I/O: Yamaha YM2149F (AY‑3‑8910 compatible) provides 3 tone + noise channels and two 8‑bit I/O ports used by ST for printer and control lines.<ref>{{cite web |url=https://temlib.org/AtariForumWiki/index.php/Yamaha_YM2149_Manual |title=Yamaha YM2149 Manual |publisher=AtariForumWiki |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://atarimuseum.ctrl-alt-rees.com/computers/16bits/STINTERN.htm |title=Atari ST Internals – YM2149 registers and I/O |publisher=Ctrl‑Alt‑Rees Atari Museum mirror |access-date=2025-08-13}}</ref>


== Input/Output and Expansion ==
== Input/Output and Expansion ==
Every external connector on the 520ST (original short case, external PSU and external floppy) is documented below. Pinouts are per Atari manuals and established community references.
External connectors and electrical specs (original 520ST “short case”; all connectors are on the rear unless noted)
* RGB/mono monitor: 13‑pin DIN female, carrying analog RGB (0.7 Vp‑p), composite sync or composite video (on modulator‑equipped units), monochrome TTL video, mono audio out, and mono audio in. Includes “mono detect” (Pin 4) which forces 640×400/71 Hz mode when grounded.<ref>{{cite web |url=https://info-coach.fr/atari/hardware/interfaces.php |title=Atari ST Interfaces / Cables – DIN‑13 monitor details |publisher=info-coach.fr |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://old.pinouts.ru/Video/AtariStMonitor_pinout.shtml |title=Atari ST monitor pinout |publisher=pinouts.ru |access-date=2025-08-13}}</ref>
* Video/monitor: 13‑pin DIN female. Signals: analog RGB (0–1.0 Vpp, 75 Ω), separate H/V sync (TTL, active low, ~3.3 kΩ source), monochrome TTL video output, composite video (only if RF modulator/composite encoder present; on pure 520ST usually composite sync only), mono audio out and audio in, +12 V pull‑up on pin 8, GPO on pin 3, and “mono detect” (pin 4) that forces 640×400/71 Hz when grounded.<ref>{{cite web |url=https://www.oldcomputers.it/parts/atari/1040STF/docs/connettore_monitor_st.htm |title=Atari ST monitor connector, levels and modes |publisher=oldcomputers.it |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://info-coach.fr/atari/hardware/interfaces.php |title=Atari ST Interfaces: Video DIN‑13 pinout |publisher=info-coach.fr |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://old.pinouts.ru/Video/AtariStMonitor_pinout.shtml |title=Atari ST monitor pinout |publisher=pinouts.ru |access-date=2025-08-13}}</ref>
* Serial (RS‑232C): DB‑25 male; line drivers/receivers typically MC1488/MC1489 on board; handled by MFP 68901 for asynchronous serial I/O.<ref>{{cite web |url=https://www.manualslib.com/manual/2170364/Atari-520ste.html |title=Atari 520/1040 STe Field Service Manual (I/O overview; 1488/1489 shown) |publisher=ManualsLib |date=1991 |access-date=2025-08-13}}</ref>
* Serial (MODEM): DB‑25 male, RS‑232C subset using MC1488/1489‑style line drivers; DTR/RTS come from PSG I/O, CTS to MFP input (edge‑sensitive).<ref>{{cite web |url=https://info-coach.fr/atari/hardware/interfaces.php |title=Atari Serial Interface pinout and notes |publisher=info-coach.fr |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://www.manualslib.com/manual/2170364/Atari-520ste.html |title=Atari 520/1040STE Field Service Manual (I/O schematics include 1488/1489) |publisher=ManualsLib |date=1991 |access-date=2025-08-13}}</ref>
* Parallel printer: DB‑25 female (Centronics‑style handshaking; unidirectional data 0–7 with Busy and Strobe).<ref>{{cite web |url=https://www.manualslib.com/manual/2170364/Atari-520ste.html |title=Atari 520/1040 STe Field Service Manual |publisher=ManualsLib |date=1991 |access-date=2025-08-13}}</ref>
* Parallel (printer): DB‑25 female, 8‑bit data (pins 2–9) driven by YM2149 Port B, STROBE on pin 1 (from YM2149 Port A), BUSY on pin 11 to MFP; other Centronics status pins are not implemented on ST.<ref>{{cite web |url=https://www.bighole.nl/pub/mirror/homepage.ntlworld.com/kryten_droid/Atari/ST/spg/st_prog_guide_1.htm |title=ST Parallel Interface (signals and rates) |publisher=Concise ST Programmer’s Reference (mirror) |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://info-coach.fr/atari/hardware/interfaces.php |title=Atari Parallel Interface pinout |publisher=info-coach.fr |access-date=2025-08-13}}</ref>
* MIDI: 2× 5‑pin DIN (MIDI IN and MIDI OUT/THRU), opto‑isolated input, serviced by one of the MC6850 ACIAs.<ref>{{cite web |url=https://www.bighole.nl/pub/mirror/homepage.ntlworld.com/kryten_droid/Atari/ST/spg/st_prog_guide_1.htm |title=Concise Atari ST 68000 Programmer's Reference Guide – Intelligent Keyboard & MIDI |publisher=bighole.nl |access-date=2025-08-13}}</ref>
* MIDI: two DIN‑5 female (IN and combined OUT/THRU wiring). ACIA‑driven at 31.25 kbaud (500 kHz ÷16). Note that the ST’s MIDI OUT jack carries both OUT and THRU via nonstandard pin usage; use cables with only pins 4/5/2 wired for standard gear.<ref>{{cite web |url=https://info-coach.fr/atari/hardware/interfaces.php |title=Atari MIDI connectors (special OUT/THRU wiring) |publisher=info-coach.fr |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://www.muzines.co.uk/articles/atari-520st/9092 |title=Atari 520ST – MIDI hardware |publisher=E&MM |date=1985-07 |access-date=2025-08-13}}</ref>
* Floppy external drive: 14‑pin round DIN (external SF354/SF314). WD1772 set for 250 kbit/s DD; early systems standard single‑sided 360 KB, later double‑sided 720 KB with SF314.<ref>{{cite web |url=https://archive.org/download/Atari_520ST_Owners_Manual_Rev._B_1985/Atari_520ST_Owners_Manual_Rev._B_1985.pdf |title=Atari 520ST Owner's Manual (Rev. B) – Appendix E Specs |publisher=Atari Corporation |date=1985 |access-date=2025-08-13}}</ref>
* External floppy: 14‑pin circular DIN female, Shugart‑style signals (Read Data, Index, Step, Direction, Write Data, Write Gate, Track 0, WP, Side 0 select, Drive selects, Motor On). Usually pin‑for‑pin straight‑through cable; model straps determine which select is B: by default.<ref>{{cite web |url=https://info-coach.fr/atari/hardware/interfaces.php |title=Floppy Disc Connector (DIN‑14) |publisher=info-coach.fr |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://old.pinouts.ru/HD/AtariFloppyPort_pinout.shtml |title=Atari Floppy port pinout |publisher=pinouts.ru |access-date=2025-08-13}}</ref>
* ACSI hard‑disk/Laser printer: DB‑19 female (“DMA” port). Bus mastered by Atari DMA chip; nominal 10 Mbit/s transfer capability.<ref>{{cite web |url=https://archive.org/download/Atari_520ST_Owners_Manual_Rev._B_1985/Atari_520ST_Owners_Manual_Rev._B_1985.pdf |title=Atari 520ST Owner's Manual (Rev. B) – Appendix E Specs |publisher=Atari Corporation |date=1985 |access-date=2025-08-13}}</ref>
* ACSI “DMA” (hard disk/laser printer): DB‑19 female. 8‑bit data bus D0..D7 plus /CS, IRQ, /RST, ACK, A1, R/W, REQ and multiple grounds; straight DB‑19M‑to‑DB‑19M cable.<ref>{{cite web |url=https://info-coach.fr/atari/hardware/interfaces.php |title=Atari DMA/ACSI Connector pinout |publisher=info-coach.fr |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://old.pinouts.ru/ParallelPorts/AtariAcsiDma_pinout.shtml |title=Atari ACSI DMA pinout |publisher=pinouts.ru |access-date=2025-08-13}}</ref>
* Mouse/joysticks: Two DE‑9 male (Port 0 shared with mouse). Pinout per Atari: 1 Up, 2 Down, 3 Left, 4 Right, 5 NC (mouse middle), 6 Fire, 7 +5 V, 8 GND, 9 second Fire (mouse right).<ref>{{cite web |url=https://archive.org/download/Atari_520ST_Owners_Manual_Rev._B_1985/Atari_520ST_Owners_Manual_Rev._B_1985.pdf |title=Atari 520ST Owner's Manual (Rev. B) – Appendix D/E Connector Pinouts |publisher=Atari Corporation |date=1985 |access-date=2025-08-13}}</ref>
* Cartridge: 40‑contact double‑sided edge connector supporting up to 128 KB ROM (A1–A15, D0–D15, LDS/UDS, ROM selects, +5 V).<ref>{{cite web |url=https://info-coach.fr/atari/hardware/interfaces.php |title=Atari Cartridge Interface pinout |publisher=info-coach.fr |access-date=2025-08-13}}</ref>
* Cartridge: 40‑way edge connector, 128 KB ROM address space.<ref>{{cite web |url=https://archive.org/download/Atari_520ST_Owners_Manual_Rev._B_1985/Atari_520ST_Owners_Manual_Rev._B_1985.pdf |title=Atari 520ST Owner's Manual (Rev. B) – Appendix E Specs |publisher=Atari Corporation |date=1985 |access-date=2025-08-13}}</ref>
* Joystick/mouse: two DE‑9 male (underside/front right). Port 0 is mouse/joystick; Port 1 joystick; +5 V on pin 7; ground on pin 8.<ref>{{cite web |url=https://info-coach.fr/atari/hardware/interfaces.php |title=Mouse/Joystick connectors |publisher=info-coach.fr |access-date=2025-08-13}}</ref>
* Power: External AC‑powered PSU feeding +5 V, +12 V, −12 V DC to a 7‑pin round DIN on the computer (+5 V @ ~2 A typical load per manual).<ref>{{cite web |url=https://archive.org/download/Atari_520ST_Owners_Manual_Rev._B_1985/Atari_520ST_Owners_Manual_Rev._B_1985.pdf |title=Atari 520ST Owner's Manual (Rev. B) – Appendix E Specs |publisher=Atari Corporation |date=1985 |access-date=2025-08-13}}</ref>
* Power (520ST/260ST external PSU): 7‑pin round DIN on computer: +5 V (multiple pins), +12 V, −12 V, grounds. Typical Atari spec: +5 V up to ~3 A, +12 V ~0.03–1 A (model‑dependent), −12 V ~0.03 A (used by RS‑232).<ref>{{cite web |url=https://wiki.icomp.de/wiki/Powersupply_FAQ |title=Power Supply FAQ – Atari 260/520ST 7‑pin DIN pinout (PS31/C070102‑3) |publisher=Individual Computers Wiki |access-date=2025-08-13}}</ref>


== Gallery ==
== Gallery ==
<gallery>
The original 520ST uses the “short‑case” shell (no internal drive/PSU) and shipped with an external SF354 3.5" drive and separate PSU brick. Regional color and badge variations exist; display was typically via SC1224 color or SM124 mono monitor.<ref>{{cite web |url=https://www.atarimagazines.com/v4n4/interiors.php |title=Interiors: Opening up the 520ST |publisher=Antic |date=1985-08 |access-date=2025-08-13}}</ref>
File:Atari 520ST.jpg|Atari 520ST (original short case with external PSU and external floppy).
File:Atari 520ST motherboard C070243.jpg|Motherboard C070243 (typical early 520ST; 6 ROM sockets visible).  
File:Atari ST SC1224.jpg|SC1224 RGB monitor (15.75 kHz color) used with low/medium‑res modes.
File:Atari SM124.jpg|SM124 monochrome monitor (640×400 @ ~71.2 Hz).
</gallery>


== Display and Graphics ==
== Display and Graphics ==
Video is generated by the Shifter (C025914), fed by GLUE/MMU arbitration from RAM:
Video subsystem (Shifter + GLUE/MMU) characteristics:
* Modes and timings (region‑dependent): Low 320×200×4bpp (16 colors), Medium 640×200×2bpp (4 colors), High 640×400×1bpp (mono). Color modes: 15.75 kHz H with 50 Hz (PAL) or 60 Hz (NTSC) V; high‑res mono: ~35.7 kHz H, ~71.2 Hz V.<ref>{{cite web |url=https://temlib.org/AtariForumWiki/index.php/Flat_Panel_Displays |title=The various Atari ST display modes |publisher=AtariForumWiki |access-date=2025-08-13}}</ref>
* Modes: 320×200 4bpp (16 colors), 640×200 2bpp (4 colors), 640×400 1bpp mono. Color modes at 15.7 kHz H with 50 Hz PAL or 60 Hz NTSC V; mono at ~35.7 kHz H and ~71.5 Hz V.<ref>{{cite web |url=https://temlib.org/AtariForumWiki/index.php/Flat_Panel_Displays |title=Atari ST display modes and timings |publisher=AtariForumWiki |access-date=2025-08-13}}</ref>
* Palette: 9‑bit RGB (3:3:3) = 512 possible colors; up to 16 simultaneously in low‑res, 4 in medium; mono mode is black/white at 640×400.<ref>{{cite web |url=https://en.wikipedia.org/wiki/Atari_ST |title=Atari ST |publisher=Wikipedia |date=2025-08-11 |access-date=2025-08-13}}</ref>
* Palette: 9‑bit RGB (3:3:3), 512 total colors; up to 16 onscreen in low‑res, 4 in medium; mono is black/white only.<ref>{{cite web |url=https://en.wikipedia.org/wiki/Atari_ST |title=Atari ST |publisher=Wikipedia |date=2025-08-11 |access-date=2025-08-13}}</ref>
* Hardware features: No hardware sprites; CPU‑driven blits (pre‑STE models) though late STs may include optional BLiTTER add‑on on some boards (not standard on the 520ST).<ref>{{cite web |url=https://en.wikipedia.org/wiki/Atari_ST |title=Atari ST |publisher=Wikipedia |date=2025-08-11 |access-date=2025-08-13}}</ref>
* Hardware features: No hardware sprites or blitter on the original 520ST; some later STF/FM boards accept an optional BLiTTER (PLCC‑68) upgrade footprint but it was not standard on 520ST.<ref>{{cite web |url=https://forums.atariage.com/topic/232054-520stfm-blitter-upgrade/ |title=520STf/m Blitter upgrade experiences |publisher=AtariAge Forums |date=2014-11 |access-date=2025-08-13}}</ref>
* Video outputs (DIN‑13): RGB (pins 6/7/10), separate HSync (9)/VSync (12), Monochrome video (11), Audio Out (1), Audio In (5), “Mono detect” (4), and +12 V (pin 8; ground on early 520ST). Composite sync/video appears on pin 2 only on modulator‑equipped units; otherwise composite sync only.<ref>{{cite web |url=https://info-coach.fr/atari/hardware/interfaces.php |title=Atari ST Interfaces / Cables – DIN‑13 monitor details |publisher=info-coach.fr |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://old.pinouts.ru/Video/AtariStMonitor_pinout.shtml |title=Atari ST monitor pinout |publisher=pinouts.ru |access-date=2025-08-13}}</ref>
* Output levels and pins (DIN‑13): RGB pins 6/7/10; HSync 9, VSync 12; mono video 11; audio out 1; audio in 5; +12 V pull‑up on pin 8; ground 13; mono detect pin 4 (tie low for SM124 mode).<ref>{{cite web |url=https://www.oldcomputers.it/parts/atari/1040STF/docs/connettore_monitor_st.htm |title=ST monitor connector (pinout/levels) |publisher=oldcomputers.it |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://old.pinouts.ru/Video/AtariStMonitor_pinout.shtml |title=Atari ST monitor pinout |publisher=pinouts.ru |access-date=2025-08-13}}</ref>


== PCB Schematics & Service Manual ==
== PCB Schematics & Service Guide ==
Motherboard families and service references commonly encountered in 520ST/520STF/520STFM repairs.
Motherboard families and identifying service references commonly seen on 520ST/520STM:
; Motherboard assemblies (selection)
{| class="wikitable"
{| class="wikitable"
! Assembly / PBA !! Typical model(s) !! Revision(s) seen !! Notes
! Assembly / PBA !! Typical models !! Revisions seen !! Notable identifiers / notes
|-
|-
| C070115 || Early 260/520ST || Rev. 2 || Early short‑case; 2‑ROM (boot TOS) or 6‑ROM footprints present.<ref>{{cite web |url=https://github.com/a2ff/splitrom |title=Atari ST ROM layouts and motherboards |publisher=GitHub (splitrom) |access-date=2025-08-13}}</ref>
| C070115 || 260/520ST (very early) || Rev. 2 || Earliest 520ST board reported; footprints for 2‑ROM boot TOS and 6‑ROM 192 KB TOS; minimal EMI chokes.<ref>{{cite web |url=https://forums.atariage.com/topic/319794-almost-unknown-atari-st-schematics/ |title=(Almost) Unknown Atari ST schematics |publisher=AtariAge Forums |date=2021-04-27 |access-date=2025-08-13}}</ref>
|-
|-
| C070231 || 260/520ST || — || 1985 schematic reconstructed to KiCad (community).<ref>{{cite web |url=https://forums.atariage.com/topic/367081-conversion-of-the-schematics-of-the-atari-260520st-motherboard-into-kicad/ |title=Conversion of the schematics of the Atari 260/520ST motherboard into KiCad |publisher=AtariAge Forums |date=2024-05-25 |access-date=2025-08-13}}</ref>
| C070231 || 260/520ST || — || Factory schematics drawing C070112 (Atari Japan); full community KiCad reconstruction available for repair work.<ref>{{cite web |url=https://archive.org/details/Atari_520ST_Schematic_1985 |title=Atari 520ST Schematic (1985), drawing set |publisher=Internet Archive |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://forums.atariage.com/topic/367081-conversion-of-the-schematics-of-the-atari-260520st-motherboard-into-kicad/ |title=KiCad conversion of Atari 260/520ST C070231 |publisher=AtariAge Forums |date=2024-05-25 |access-date=2025-08-13}}</ref>
|-
|-
| C070243 || 520ST || Revs C/E/F/H/I || Common early 520ST board; many variants 2‑ or 6‑ROM.<ref>{{cite web |url=https://docs.sidecartridge.com/sidecartridge-tos/compatibility/ |title=Motherboard model numbers and ROM configurations |publisher=Sidecartridge Docs |access-date=2025-08-13}}</ref>
| C070243 || 520ST/520STM || Rev. C, H, I || Later short‑case boards; added numerous EMI chokes vs. C070115; common target for 1–4 MB RAM mods.<ref>{{cite web |url=https://retrocomputing.stackexchange.com/questions/21618/why-do-some-atari-st-motherboards-include-many-inductors |title=Why do some Atari ST motherboards include many inductors? |publisher=Retrocomputing StackExchange |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://wiki.console5.com/wiki/Atari_ST |title=Atari ST recap notes by board (C070243 Rev C/H) |publisher=Console5 TechWiki |access-date=2025-08-13}}</ref>
|-
| C103414‑001 || 520STFM || Rev. 1 / 1.1 || Later STFM (integrated floppy + RF); 2‑ or 6‑ROM.<ref>{{cite web |url=https://docs.sidecartridge.com/sidecartridge-tos/compatibility/ |title=Motherboard model numbers and ROM configurations |publisher=Sidecartridge Docs |access-date=2025-08-13}}</ref>
|}
|}
; Schematics and service docs
Service/schematic references
* Atari 520ST Schematic (1985), 3 pages (core logic, video, I/O).<ref>{{cite web |url=https://archive.org/details/Atari_520ST_Schematic_1985 |title=Atari 520ST Schematic [1985] |publisher=Internet Archive |access-date=2025-08-13}}</ref>
* Early factory schematics: “Atari (Japan) Corporation” drawing C070112 (1985) covering 260/520ST main logic; scans circulate online.<ref>{{cite web |url=https://archive.org/details/Atari_520ST_Schematic_1985 |title=Atari 520ST Schematic (1985) |publisher=Internet Archive |access-date=2025-08-13}}</ref>
* Atari 1040ST Schematic Rev C (C070787, 1986‑12‑26) – useful for STf/fm video/GLUE/MMU references.<ref>{{cite web |url=https://archive.org/details/Atari_1040ST_Schematic_Rev_C_C070787_Dec_26_1986 |title=Atari 1040ST Schematic Rev C C070787 [Dec 26, 1986] |publisher=Internet Archive |access-date=2025-08-13}}</ref>
* 520/1040STE Field Service Manual (C302481‑001 Rev A, Aug 1991) includes many circuits compatible in concept (MFP, YM2149, DMA, WD1772) and is frequently referenced for troubleshooting I/O sections shared with ST family.<ref>{{cite web |url=https://www.manualslib.com/manual/2170364/Atari-520ste.html |title=Atari STe 520/1040 Field Service Manual, C302481‑001 |publisher=ManualsLib |date=1991 |access-date=2025-08-13}}</ref>
* Field Service manual (STe; later architecture but same 68000, WD1772/ACSI/I/O blocks; includes port pin summaries and diagnostic flow).<ref>{{cite web |url=https://www.manualslib.com/manual/2170364/Atari-520ste.html |title=Atari 520/1040 STe Field Service Manual (C302481‑001 Rev. A) |publisher=ManualsLib |date=1991 |access-date=2025-08-13}}</ref>


== Memory and Storage ==
== Memory and Storage ==
RAM/ROM layout and controllers used on the 520ST:
RAM organization and ROM layout
* Main memory: 512 KB using 16×256‑Kbit DRAMs; many 520ST+ shipped with 1 MB (16×1‑Mbit). MMU (C025912/C100109) provides RAS/CAS multiplexing and DRAM timing.<ref>{{cite web |url=https://mikrosk.github.io/doitarchive/doit_st/0303.htm |title=DOIT ST: Parts list (MMU) |publisher=DOIT_ST archive |access-date=2025-08-13}}</ref>
* Standard RAM: 512 KB on system board, typically 16× 256k×1 DRAMs (varies by vendor), arranged as two 8‑bit banks to form the 16‑bit data path. Numerous later replacement boards allow 1–4 MB by adding new DRAM modules or SIMMs (wiring to MMU MAD/CAS/RAS lines as required).<ref>{{cite web |url=https://forums.atariage.com/topic/337575-520st-ram-upgrade-question/page/2/ |title=520ST RAM upgrade discussion, C070243 boards |publisher=AtariAge Forums |date=2022-09-14 |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://www.pcbway.com/project/shareproject/STRAM_4MB_Atari_520ST_M_Expansion_692e0348.html |title=STRAM 4MB Atari 520ST(M) Expansion |publisher=PCBWay |date=2023-06-07 |access-date=2025-08-13}}</ref>
* ROM: Very early 520ST shipped with a 16 KB boot ROM (“TOS on disk”) consuming ~206 KB RAM when loaded; later machines used 192 KB TOS 1.00 in 6× 27C256 (or 2× 1‑Mbit) ROMs at $FC0000–$FEFFFF.<ref>{{cite web |url=https://archive.org/download/Atari_520ST_Owners_Manual_Rev._B_1985/Atari_520ST_Owners_Manual_Rev._B_1985.pdf |title=Atari 520ST Owner's Manual (Rev. B) – Specs show 16,384‑byte ROM for boot units |publisher=Atari Corporation |date=1985 |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://en.wikipedia.org/wiki/Atari_TOS |title=Atari TOS |publisher=Wikipedia |date=2024-12-01 |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://atarimuseum.ctrl-alt-rees.com/computers/16bits/STINTERN.htm |title=Atari ST internals quick map (ROM base addresses) |publisher=Ctrl‑Alt‑Rees (Atari Museum mirror) |access-date=2025-08-13}}</ref>
* ROM/TOS: Early machines shipped with tiny 2‑chip boot ROMs that loaded TOS from disk; later 192 KB TOS 1.00 in 6× 32 KB DIPs; subsequent 192 KB TOS 1.02/1.04 appear in 2‑chip sets; part numbers for 6‑chip US TOS 1.00 include CO26160..CO26165.<ref>{{cite web |url=https://mikrosk.github.io/doitarchive/doit_st/0f0601.htm |title=TOS ROM sizes and families |publisher=DOIT_ST archive |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://www.best-electronics-ca.com/custom-i.htm |title=Best Electronics – Atari TOS ROM part numbers |publisher=Best Electronics |access-date=2025-08-13}}</ref>
* Memory map highlights (ST/early TOS): TOS ROM at $FC0000–$FEFFFF (TOS 1.00/1.02/1.04); cartridge space at $FA0000; hardware registers (e.g., video base $FFFF8201, palette $FFFF8240, MFP at $FFFAxx).<ref>{{cite web |url=https://atarimuseum.ctrl-alt-rees.com/computers/16bits/STINTERN.htm |title=Atari ST internals quick map |publisher=Ctrl‑Alt‑Rees |access-date=2025-08-13}}</ref>
* Floppy subsystem: WD1772 FDC at 8 MHz (250 kbit/s). Standard external single‑sided 3.5" SF354 (360 KB). The WD1772‑02‑02 variant often tolerates 16 MHz for 1.44 MB HD mods with appropriate gating and TOS support.<ref>{{cite web |url=https://mikrosk.github.io/doitarchive/doit_st/0b03.htm |title=HD Disk ST (WD1772 02‑02 at 16 MHz) |publisher=DOIT_ST archive |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://exxosforum.co.uk/atari/last/floppy/index.htm |title=LaST 1.44 MB mod notes |publisher=exxosforum |access-date=2025-08-13}}</ref>
* Floppy: WD1772 controller; SF354 3.5″ SSDD (360 KB) initially, SF314 3.5″ DSDD (720 KB) later. WD1772 is clocked at 8 MHz (250 kbit/s DD); certain WD1772‑02‑02 chips tolerate 16 MHz for HD mods.<ref>{{cite web |url=https://archive.org/download/Atari_520ST_Owners_Manual_Rev._B_1985/Atari_520ST_Owners_Manual_Rev._B_1985.pdf |title=Atari 520ST Owner's Manual (Rev. B) – Floppy capacity |publisher=Atari Corporation |date=1985 |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://mikrosk.github.io/doitarchive/doit_st/040a.htm |title=DOIT ST: AJAX/WD1772 notes |publisher=DOIT_ST archive |access-date=2025-08-13}}</ref>
* Hard disks: External ACSI devices via DB‑19; up to eight chained targets with simple 8‑bit protocol similar to early SCSI (not electrically SCSI). Used by Atari SH204/205 and MegaFile drives and the SLM laser printer.<ref>{{cite web |url=https://info-coach.fr/atari/hardware/interfaces.php |title=Atari DMA/ACSI interface |publisher=info-coach.fr |access-date=2025-08-13}}</ref>
* Hard disks: ACSI port (DB‑19), DMA‑based; SH204 and later drives supported via AHDI. Manual quotes 10 Mbit/s peak bus rate.<ref>{{cite web |url=https://archive.org/download/Atari_520ST_Owners_Manual_Rev._B_1985/Atari_520ST_Owners_Manual_Rev._B_1985.pdf |title=Atari 520ST Owner's Manual (Rev. B) – Appendix E |publisher=Atari Corporation |date=1985 |access-date=2025-08-13}}</ref>
 
== Related Pages ==
* [[Atari 520ST General Maintenance]]
* [[Atari 520ST Troubleshooting Guide]]
* [[Atari 520ST Capacitor Replacement Guide]]
* [[Atari 520ST Floppy Drive Upgrade (SF354→SF314)]]
* [[Atari ST ACSI Hard Disk Setup Guide]]


== Sound Capabilities ==
== Sound Capabilities ==
The 520ST uses a Yamaha YM2149F (AY‑3‑8910 compatible) PSG:
* PSG: Yamaha YM2149F (AY‑3‑8910 derivative) – 3 independent square‑wave tone channels plus 1 noise source; 5‑bit amplitude registers with 5‑bit envelope generator and 8 preset shapes; 8 octave range. No analog filter.<ref>{{cite web |url=https://temlib.org/AtariForumWiki/index.php/Yamaha_YM2149_Manual |title=YM2149 manual (features) |publisher=AtariForumWiki |access-date=2025-08-13}}</ref>
* 3 independent square‑wave tone channels (A/B/C) plus 1 white noise generator; 16‑level per‑channel volume with shared programmable ADSR‑style envelope generator; mixer for tone/noise per channel.<ref>{{cite web |url=https://en.wikipedia.org/wiki/Atari_ST |title=Atari ST (sound overview) |publisher=Wikipedia |date=2025-08-11 |access-date=2025-08-13}}</ref>
* Digital audio: No dedicated PCM in 520ST; CPU‑driven sample playback possible by rapid volume register updates or timer‑driven DAC on parallel port in software (common in demos and some games).<ref>{{cite web |url=https://www.goto10retro.com/p/sounds-of-the-atari-st |title=Sounds of the Atari ST (historical overview) |author=Paul Lefebvre |publisher=GoTo10Retro |date=2024-01-10 |access-date=2025-08-13}}</ref>
* Output: monaural line/speaker feed on monitor DIN‑13 pin 1; internal amplifier in Atari monitors (SM124/SC1224).<ref>{{cite web |url=https://info-coach.fr/atari/hardware/interfaces.php |title=Atari ST Interfaces / Cables – audio pins |publisher=info-coach.fr |access-date=2025-08-13}}</ref>
* Audio I/O: Mono line‑level out and an audio‑in on the 13‑pin monitor port (approx. 1 Vpp nominal).<ref>{{cite web |url=https://www.oldcomputers.it/parts/atari/1040STF/docs/connettore_monitor_st.htm |title=Monitor connector – audio in/out levels |publisher=oldcomputers.it |access-date=2025-08-13}}</ref>
* Connectors: audio is via the monitor cable; no separate RCA jack on the original 520ST.


== General Maintenance ==
== General Maintenance ==
Routine service items for 520ST owners and technicians:
Basic care (brief; see dedicated maintenance page)
* Clean and re‑lube SF354/SF314 drive rails; re‑belt (if applicable) and verify index sensor alignment.
* PSU: The external PSU brick feeds +5 V, +12 V, −12 V via 7‑pin DIN; verify voltages at the plug before connecting. −12 V is primarily for RS‑232; +12 V may be lightly loaded on original 520ST (no internal drive).<ref>{{cite web |url=https://wiki.icomp.de/wiki/Powersupply_FAQ |title=Power Supply FAQ – ST DIN‑7 pinout and currents |publisher=Individual Computers |access-date=2025-08-13}}</ref>
* Reseat socketed ICs (68000, Shifter can be socketed under RF can; WD1772; ROMs).
* Caps and sockets: Later ST boards added many EMI chokes; electrolytics age—recap keyboard and main board as needed; reseat socketed ICs (GLUE/MMU/Shifter/68000/ROMs) when diagnosing random faults.<ref>{{cite web |url=https://retrocomputing.stackexchange.com/questions/21618/why-do-some-atari-st-motherboards-include-many-inductors |title=Inductors on later ST boards (EMC notes) |publisher=Retrocomputing StackExchange |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://wiki.console5.com/wiki/Atari_ST |title=Console5 ST recap notes |publisher=Console5 TechWiki |access-date=2025-08-13}}</ref>
* Inspect external PSU for ripple (replace with modern, properly regulated +5 V/+12 V/−12 V supply if unstable).<ref>{{cite web |url=https://www.keelog.com/atari-520st-psu-modern-gray-us-replacement-atari-520st-power-supply-us-plug/ |title=Replacement Atari 520ST PSU (specs and rails) |publisher=Keelog |access-date=2025-08-13}}</ref>
* Video cabling: Confirm monitor cable wiring (sync polarity and pin 8 +12 V) and use mono‑detect (pin 4) appropriately to force 640×400.<ref>{{cite web |url=https://old.pinouts.ru/Video/AtariStMonitor_pinout.shtml |title=ST monitor pinout |publisher=pinouts.ru |access-date=2025-08-13}}</ref>
* Keyboards: clean membrane and plungers; verify IKBD (HD6301) comms and MC6850 ACIA socket contacts.<ref>{{cite web |url=https://www.bighole.nl/pub/mirror/homepage.ntlworld.com/kryten_droid/Atari/ST/spg/st_prog_guide_3_utilities.htm |title=Concise Atari ST 68000 Programmer's Reference – IKBD |publisher=bighole.nl |access-date=2025-08-13}}</ref>
 
See the dedicated page: [[Atari 520ST General Maintenance]].


== Technical Details ==
== Technical Details ==
; Major ICs and revisions (typical)
Comprehensive IC inventory (typical 520ST) – major functions and common part numbers:
{| class="wikitable"
{| class="wikitable"
! Function !! Part numbers (examples) !! Notes
! Function !! Common part(s) / package !! Notes
|-
|-
| CPU || MC68000P8 / MC68000FN8 || 8 MHz, 24‑bit address / 16‑bit data.<ref>{{cite web |url=https://en.wikipedia.org/wiki/Atari_ST |title=Atari ST |publisher=Wikipedia |date=2025-08-11 |access-date=2025-08-13}}</ref>
| CPU || MC68000P8 (DIP‑64), MC68000FN8 (PLCC‑68) || 8.00 MHz core.<ref>{{cite web |url=https://www.alldatasheet.net/datasheet-pdf/pdf/135463/MOTOROLA/MC68000P8.html |title=MC68000P8 datasheet |publisher=Motorola |access-date=2025-08-13}}</ref>
|-
|-
| Shifter (video) || C025914‑38/‑38A; CO70713/I10356 || Generates RGB/mono from RAM fetches.<ref>{{cite web |url=https://mikrosk.github.io/doitarchive/doit_st/0303.htm |title=DOIT ST: Parts |publisher=DOIT_ST archive |access-date=2025-08-13}}</ref>
| Video “Shifter” || C025914‑38/‑38A; CO70713/I10356 || Reads DRAM and serializes pixels.<ref>{{cite web |url=https://forums.atariage.com/topic/247569-huge-list-of-new-original-atari-custom-ic-chips-transistors-etc/ |title=Atari custom IC list |publisher=AtariAge |access-date=2025-08-13}}</ref>
|-
|-
| GLUE || C025915‑38A; CO70714/I10355 || Bus/timing, interrupts, address decode.<ref>{{cite web |url=https://mikrosk.github.io/doitarchive/doit_st/0303.htm |title=DOIT ST: Parts |publisher=DOIT_ST archive |access-date=2025-08-13}}</ref>
| GLUE || C025915‑38A || Bus/timing decode, video timing assist.<ref>{{cite web |url=https://forums.atariage.com/topic/247569-huge-list-of-new-original-atari-custom-ic-chips-transistors-etc/ |title=Atari custom IC list |publisher=AtariAge |access-date=2025-08-13}}</ref>
|-
|-
| MMU || C025912‑38; C100109/I10353 || DRAM control, video base.<ref>{{cite web |url=https://mikrosk.github.io/doitarchive/doit_st/0303.htm |title=DOIT ST: Parts |publisher=DOIT_ST archive |access-date=2025-08-13}}</ref>
| MMU (DRAM) || C025912‑38; later C100109 || Row/col multiplex/refresh to DRAM.<ref>{{cite web |url=https://forums.atariage.com/topic/247569-huge-list-of-new-original-atari-custom-ic-chips-transistors-etc/ |title=Atari custom IC list |publisher=AtariAge |access-date=2025-08-13}}</ref>
|-
|-
| DMA (ACSI/floppy) || C025913‑38 || ACSI/HDD and FDD DMA handshakes.<ref>{{cite web |url=https://forums1128.rssing.com/chan-4289726/all_p480.html |title=Atari custom IC list |publisher=RSSing (AtariAge mirror) |access-date=2025-08-13}}</ref>
| DMA (ACSI/FDD) || C025913‑38 || 8‑bit ACSI and FDC DMA, IRQ/DRQ handshake.<ref>{{cite web |url=https://mikrosk.github.io/doitarchive/doit_st/0904.htm |title=DMA, ROM, and WD1772 photo |publisher=DOIT_ST |access-date=2025-08-13}}</ref>
|-
|-
| Floppy controller || WD1772‑00‑02 / WD1772‑02‑02 || 8 MHz DD operation; overclockable variants for HD mods.<ref>{{cite web |url=https://www.exxosforum.co.uk/atari/store2/0268.html |title=WD1772 00‑02 floppy controller |publisher=exxosforum store |access-date=2025-08-13}}</ref>
| Floppy controller || WD1772‑00‑02 / ‑02‑02 || 250 kbit/s DD; many ‑02‑02 parts OK at 16 MHz for HD mods.<ref>{{cite web |url=https://mikrosk.github.io/doitarchive/doit_st/0b03.htm |title=HD Disk ST |publisher=DOIT_ST |access-date=2025-08-13}}</ref>
|-
|-
| MFP || MC68901 || Timers/interrupts/serial.<ref>{{cite web |url=https://www.bighole.nl/pub/mirror/homepage.ntlworld.com/kryten_droid/Atari/ST/spg/st_prog_guide_1.htm |title=ST Programmer's Guide – MFP |publisher=bighole.nl |access-date=2025-08-13}}</ref>
| MFP (timers/IRQs/U(S)ART) || MC68901 || 200 Hz system tick, vectorized interrupts.<ref>{{cite web |url=https://www.bighole.nl/pub/mirror/homepage.ntlworld.com/kryten_droid/Atari/ST/spg/st_prog_guide_1.htm |title=MFP details |publisher=Concise ST Prog Ref |access-date=2025-08-13}}</ref>
|-
|-
| ACIAs || 2× MC6850 || Keyboard (IKBD) and MIDI UARTs.<ref>{{cite web |url=https://www.atarimagazines.com/compute/issue73/st_hints_tips.php |title=ST Hints & Tips – 6301 IKBD and ACIA |publisher=Compute! |access-date=2025-08-13}}</ref>
| ACIAs (MIDI/IKBD) || 2× MC6850 || 7812.5 baud link to IKBD; 31.25 kbaud MIDI.<ref>{{cite web |url=https://www.muzines.co.uk/articles/atari-520st/9092 |title=Atari 520ST (MIDI hardware) |publisher=E&MM |date=1985-07 |access-date=2025-08-13}}</ref>
|-
|-
| Sound || Yamaha YM2149F || 3‑voice PSG with noise; mono output.<ref>{{cite web |url=https://en.wikipedia.org/wiki/Atari_ST |title=Atari ST |publisher=Wikipedia |date=2025-08-11 |access-date=2025-08-13}}</ref>
| Sound/PIO || YM2149F || 3‑voice PSG + I/O (printer strobe/data, FDD selects, RTS/DTR).<ref>{{cite web |url=https://atarimuseum.ctrl-alt-rees.com/computers/16bits/STINTERN.htm |title=ST Internals – YM2149 regs |publisher=Ctrl‑Alt‑Rees |access-date=2025-08-13}}</ref>
|-
| RS‑232 transceivers || MC1488, MC1489 (or equivalents) || Level conversion for DB‑25 serial.<ref>{{cite web |url=https://www.manualslib.com/manual/2170364/Atari-520ste.html |title=STE Service Manual (I/O section) |publisher=ManualsLib |date=1991 |access-date=2025-08-13}}</ref>
|}
|}


; Power rails and consumption
== System Architecture at a Glance ==
* External PSU outputs +5 V (≈2 A), +12 V (≈30 mA), −12 V (≈30 mA) to the computer (round DIN‑7); region‑specific AC mains by PSU model (120 V/60 Hz in U.S., 220–240 V/50 Hz in Europe).<ref>{{cite web |url=https://archive.org/download/Atari_520ST_Owners_Manual_Rev._B_1985/Atari_520ST_Owners_Manual_Rev._B_1985.pdf |title=Atari 520ST Owner's Manual (Rev. B) – Appendix E |publisher=Atari Corporation |date=1985 |access-date=2025-08-13}}</ref>
* Address map highlights: $FA0000–$FBFFFF cartridge (128 KB), $FC0000–$FEFFFF system ROM (192 KB), $FF8800 PSG, $FF8600 DMA, $FFFAxx MFP, $FFFC00/04 ACIAs; RAM from $000000 upward (unified).<ref>{{cite web |url=https://temlib.org/AtariForumWiki/index.php/Atari_ST/STe/MSTe/TT/F030_Hardware_Register_Listing |title=Atari ST hardware registers and memory map |publisher=AtariForumWiki |access-date=2025-08-13}}</ref>
* Video DMA steals cycles from 68000 during active display; worst contention in low‑res; mono mode offers highest CPU availability.<ref>{{cite web |url=https://temlib.org/AtariForumWiki/index.php/Flat_Panel_Displays |title=ST display timing/refresh |publisher=AtariForumWiki |access-date=2025-08-13}}</ref>


== System Architecture at a Glance ==
== PCB Schematics & Service Manual ==
* 68000 @ 8 MHz; GLUE decodes I/O and arbitrates bus with Shifter and DMA.
See earlier “PCB Schematics & Service Guide” for board IDs. Early official drawing: C070112 (Atari Japan), and community KiCad reconstruction for C070231 are recommended for board‑level repair tracing.<ref>{{cite web |url=https://archive.org/details/Atari_520ST_Schematic_1985 |title=Atari 520ST Schematic (1985) |publisher=Internet Archive |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://forums.atariage.com/topic/367081-conversion-of-the-schematics-of-the-atari-260520st-motherboard-into-kicad/ |title=KiCad conversion for 260/520ST mainboard |publisher=AtariAge |date=2024-05-25 |access-date=2025-08-13}}</ref>
* 512 KB RAM (typical), 192 KB TOS 1.xx ROM on later units; earliest units boot TOS from disk via 16 KB boot ROM.
* Video via Shifter from RAM; 512‑color palette (3:3:3), 16/4 colors on low/med, 640×400 mono on SM124.
* I/O: DB‑25 serial and parallel, DIN‑13 video+audio, DB‑19 ACSI DMA, 14‑pin DIN floppy, two DE‑9 joystick/mouse, 2× DIN‑5 MIDI, 40‑way cartridge.
* External PSU rails +5/+12/−12 V; computer contains only low‑voltage DC circuitry (no internal analog PSU board on 520ST).<ref>{{cite web |url=https://archive.org/download/Atari_520ST_Owners_Manual_Rev._B_1985/Atari_520ST_Owners_Manual_Rev._B_1985.pdf |title=Atari 520ST Owner's Manual (Rev. B) |publisher=Atari Corporation |date=1985 |access-date=2025-08-13}}</ref>


== Apple Service Manual ==
== Apple Service Manual ==
Not applicable. The 520ST is an Atari product; for service procedures use the Atari ST schematics and field service documentation listed above, not Apple references.
Not applicable to the Atari 520ST. For ST service procedures, refer instead to the early 520ST schematic set (C070112) and the 520/1040STE Field Service Manual for comparable circuits and troubleshooting trees.<ref>{{cite web |url=https://archive.org/details/Atari_520ST_Schematic_1985 |title=Atari 520ST Schematic (1985) |publisher=Internet Archive |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://www.manualslib.com/manual/2170364/Atari-520ste.html |title=Atari STe 520/1040 Field Service Manual |publisher=ManualsLib |date=1991 |access-date=2025-08-13}}</ref>


== Logic Board & Analog Board Schematics ==
== Logic Board & Analog Board Schematics ==
The 520ST has a single main logic board; there is no separate “analog board” (that term applies to some Apple Macintosh models). For display hardware, refer to the SC1224/SM124 monitor service literature separately. Core 520ST schematics: see “PCB Schematics & Service Manual.”<ref>{{cite web |url=https://archive.org/details/Atari_520ST_Schematic_1985 |title=Atari 520ST Schematic [1985] |publisher=Internet Archive |access-date=2025-08-13}}</ref>
The 520ST uses a single logic board; there is no separate “analog board” as on compact Macs. Analog circuitry resides in external monitors (SC1224 color, SM124 mono). See monitor‑specific service docs for analog chassis; see this overview of SC1224 manufacturing variants (JVC/Goldstar/Samsung) for field notes.<ref>{{cite web |url=https://mikrosk.github.io/doitarchive/doit_st/1205.htm |title=SC1224 monitor notes (variants) |publisher=DOIT_ST archive |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://caps.wiki/wiki/Atari_SC1224 |title=Atari SC1224 (repair notes) |publisher=Caps Wiki |access-date=2025-08-13}}</ref>


== Troubleshooting ==
== Troubleshooting ==
Common field faults on early ST systems and checks:
Quick checks commonly applicable to a non‑modded 520ST:
* Black screen, no beep: verify 5 V at Shifter can and 68000; check reset chain; substitute GLUE/MMU as needed; inspect ROM seating (six‑ROM sets especially).<ref>{{cite web |url=https://www.manualslib.com/manual/2170364/Atari-520ste.html |title=Atari STe Field Service Manual – Symptom and flowcharts (applicable concepts) |publisher=ManualsLib |date=1991 |access-date=2025-08-13}}</ref>
* No video in color: verify DIN‑13 pinout, ensure HSync (9) and VSync (12) are wired; if forcing mono, ground pin 4 (mono detect) and use SM124 or compatible 71 Hz mono monitor.<ref>{{cite web |url=https://old.pinouts.ru/Video/AtariStMonitor_pinout.shtml |title=ST monitor pinout |publisher=pinouts.ru |access-date=2025-08-13}}</ref>
* No video in color but mono OK: DIN‑13 cable/pin 4 state; verify composite sync/video behavior (depends on modulator presence).<ref>{{cite web |url=https://info-coach.fr/atari/hardware/interfaces.php |title=Atari Video Connector (details on composite vs sync) |publisher=info-coach.fr |access-date=2025-08-13}}</ref>
* System powers, drive ticks, but blank screen: reseat socketed ICs (Shifter, GLUE, MMU, 68000, ROMs); oxidized sockets are common on early boards.<ref>{{cite web |url=https://www.atarimagazines.com/v4n4/interiors.php |title=Interiors: 520ST internal overview |publisher=Antic |date=1985-08 |access-date=2025-08-13}}</ref>
* Floppy errors: WD1772 socket contacts and 8 MHz clock; check drive select/jumpering on SF354/SF314; clean heads. WD1772‑02‑02 often preferred for reliability; verify motor and index sensor.<ref>{{cite web |url=https://mikrosk.github.io/doitarchive/doit_st/080103.htm |title=DOIT ST: WD1772 notes |publisher=DOIT_ST archive |access-date=2025-08-13}}</ref>
* Floppy B: not seen: check DIN‑14 drive select wiring and STF strap default (Pin 5 often wired as Drive 1 select for external B:).<ref>{{cite web |url=https://info-coach.fr/atari/hardware/interfaces.php |title=Floppy connector and BLITZ cable notes |publisher=info-coach.fr |access-date=2025-08-13}}</ref>
* ACSI device timeouts: Inspect DB‑19 connector solder joints; verify DMA (C025913‑38).<ref>{{cite web |url=https://archive.org/download/Atari_520ST_Owners_Manual_Rev._B_1985/Atari_520ST_Owners_Manual_Rev._B_1985.pdf |title=Atari 520ST Owner's Manual – ACSI overview |publisher=Atari Corporation |date=1985 |access-date=2025-08-13}}</ref>
* ACSI devices: confirm straight‑through DB‑19M cable 1:1 to device and proper termination/ID; IRQ/REQ wiring faults present as timeouts.<ref>{{cite web |url=https://info-coach.fr/atari/hardware/interfaces.php |title=DMA/ACSI pinout and cabling |publisher=info-coach.fr |access-date=2025-08-13}}</ref>
* Keyboard/mouse erratic: check IKBD 6301 comms at 7812.5 bps via the MC6850 ACIA; reseat keyboard cable.<ref>{{cite web |url=https://www.bighole.nl/pub/mirror/homepage.ntlworld.com/kryten_droid/Atari/ST/spg/st_prog_guide_1.htm |title=ST Programmer's Guide – IKBD/ACIA |publisher=bighole.nl |access-date=2025-08-13}}</ref>


== 🧠 Architecture and Processor ==
== 🧠 Architecture and Processor ==
Deep‑dive notes for developers and repair techs:
Implementation notes for engineers:
* MFP 68901 base at $FFFA01 (odd‑addressed register block); timers: A/B (high‑frequency raster/VBL uses), C (200 Hz system tick), D (baud). Interrupt vectors and masks documented in ST Programmer’s guide.<ref>{{cite web |url=https://www.bighole.nl/pub/mirror/homepage.ntlworld.com/kryten_droid/Atari/ST/spg/st_prog_guide_1.htm |title=Concise ST Programmer’s Guide – MFP registers |publisher=bighole.nl |access-date=2025-08-13}}</ref>
* The MFP’s Timer B is often used by TOS for display timing (HBLANK), Timer C drives the 200 Hz system clock; IKBD events arrive via the keyboard ACIA at 7812.5 baud (GLUE‑derived 500 kHz ÷64 for keyboard; MIDI ÷16).<ref>{{cite web |url=https://www.bighole.nl/pub/mirror/homepage.ntlworld.com/kryten_droid/Atari/ST/spg/st_prog_guide_1.htm |title=MFP timers and interrupts |publisher=Concise ST Prog Ref |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://www.bighole.nl/pub/mirror/homepage.ntlworld.com/kryten_droid/Atari/ST/spg/st_prog_guide_2.htm |title=Serial/MIDI/IKBD control |publisher=Concise ST Prog Ref |access-date=2025-08-13}}</ref>
* Video registers (Shifter/GLUE): base address high/med $FFFF8201/$FFFF8203; palette at $FFFF8240 (16 words); resolution reg $FFFF8260; mono detect via external pin 4 on DIN‑13.<ref>{{cite web |url=https://atarimuseum.ctrl-alt-rees.com/computers/16bits/STINTERN.htm |title=Atari ST internals quick map |publisher=Ctrl‑Alt‑Rees |access-date=2025-08-13}}</ref>
* Memory map summary for ROM and I/O: cartridge at $FA0000, TOS at $FC0000, PSG at $FF8800, DMA at $FF8600, ACIAs at $FFFC00/04, MFP at $FFFA00 region; align replacement ROMs accordingly (2‑chip vs 6‑chip variants).<ref>{{cite web |url=https://temlib.org/AtariForumWiki/index.php/Atari_ST/STe/MSTe/TT/F030_Hardware_Register_Listing |title=ST hardware register listing |publisher=AtariForumWiki |access-date=2025-08-13}}</ref><ref>{{cite web |url=https://github.com/a2ff/splitrom |title=TOS ROM splitter and motherboard notes |publisher=GitHub (splitrom) |access-date=2025-08-13}}</ref>
* ROM map: TOS 1.00/1.02/1.04 at $FC0000–$FEFFFF (192 KB). STE/2.06 moves to $E00000–$E3FFFF (256 KB) – relevant for ROM upgrade wiring on some STFs.<ref>{{cite web |url=https://en.wikipedia.org/wiki/Atari_TOS |title=Atari TOS |publisher=Wikipedia |date=2024-12-01 |access-date=2025-08-13}}</ref>


== Technical Documentation ==
== Technical Documentation ==
* [[Atari 520ST Owner’s Manual (Rev. B, 1985)]].<ref>{{cite web |url=https://archive.org/download/Atari_520ST_Owners_Manual_Rev._B_1985/Atari_520ST_Owners_Manual_Rev._B_1985.pdf |title=Atari 520ST Owner's Manual (Rev. B) |publisher=Atari Corporation |date=1985 |access-date=2025-08-13}}</ref>
* Atari 520ST Schematic (1985) – drawing C070112 (Atari Japan).<ref>{{cite web |url=https://archive.org/details/Atari_520ST_Schematic_1985 |title=Atari 520ST Schematic (1985) |publisher=Internet Archive |access-date=2025-08-13}}</ref>
* [[Atari 520ST Schematic (1985)]].<ref>{{cite web |url=https://archive.org/details/Atari_520ST_Schematic_1985 |title=Atari 520ST Schematic [1985] |publisher=Internet Archive |access-date=2025-08-13}}</ref>
* Conversion of the 260/520ST motherboard C070231 schematics to KiCad (community).<ref>{{cite web |url=https://forums.atariage.com/topic/367081-conversion-of-the-schematics-of-the-atari-260520st-motherboard-into-kicad/ |title=KiCad conversion for 260/520ST |publisher=AtariAge Forums |date=2024-05-25 |access-date=2025-08-13}}</ref>
* [[Atari 1040ST Schematic Rev C (C070787) – 1986]].<ref>{{cite web |url=https://archive.org/details/Atari_1040ST_Schematic_Rev_C_C070787_Dec_26_1986 |title=Atari 1040ST Schematic Rev C C070787 [Dec 26, 1986] |publisher=Internet Archive |access-date=2025-08-13}}</ref>
* Atari STe 520/1040 Field Service Manual C302481‑001 Rev A (useful for shared subsystems and diagnostics).<ref>{{cite web |url=https://www.manualslib.com/manual/2170364/Atari-520ste.html |title=Atari STe Field Service Manual |publisher=ManualsLib |date=1991 |access-date=2025-08-13}}</ref>
* [[Atari TOS Versions and ROM Configurations]].<ref>{{cite web |url=https://en.wikipedia.org/wiki/Atari_TOS |title=Atari TOS |publisher=Wikipedia |date=2024-12-01 |access-date=2025-08-13}}</ref>
* Atari 520ST Owner’s Manual (1985).<ref>{{cite web |url=https://archive.org/details/Atari_520ST_Owners_Manual_Rev._B_1985 |title=Atari 520ST Owner’s Manual, Rev. B (1985) |publisher=Internet Archive |access-date=2025-08-13}}</ref>
* [[Atari ST Interfaces and Pinouts]].<ref>{{cite web |url=https://info-coach.fr/atari/hardware/interfaces.php |title=Atari Video/Interfaces |publisher=info-coach.fr |access-date=2025-08-13}}</ref>
 
== Related Pages ==
* [[Atari 520STF]] – internal floppy version (later case/PSU variants) 
* [[Atari 520STFM]] – internal floppy and RF modulator version 
* [[Atari 1040ST]] – 1 MB model with integrated floppy/PSU (1986)<ref>{{cite web |url=https://www.atarimagazines.com/compute/issue71/electronics_show.php |title=1040ST announcement and bundles |publisher=Compute! |date=1986-02 |access-date=2025-08-13}}</ref>
* [[Mega ST]] – enhanced chassis and expansion bus 
* [[Atari SC1224]] and [[Atari SM124]] monitors (display specs/repairs)


== References ==
== References ==
Retrieved from "https://wiki.retrotechcollection.com/Atari_520ST"