Atari 520ST: Difference between revisions

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{{Infobox computer

| name = Atari 520ST

| image = [[File:~~Atari520ST~~.jpg|250px]]

| image = [[File:Atari 520ST system.jpg|250px]]

| manufacturer = Atari Corporation

| type = Home computer / personal computer

Line 19:

| 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]]

| successor = [[Atari ~~1040ST~~]]

| successor = [[Atari 1040STE]]

}}

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* 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>

* 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>

== Memory and Storage ==

RAM organization and ROM layout

* 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/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>

* 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>

* 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>

== Sound Capabilities ==

* 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>

* 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>

* 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>

== PCB Schematics & Service Guide ==

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* 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>

* 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>

~~== Memory and Storage ==~~

~~RAM organization and ROM layout~~

* 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/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>

* 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>

* 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>

~~== Sound Capabilities ==~~

* 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>

* 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>

* 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>

~~== General Maintenance ==~~

~~Basic care (brief; see dedicated maintenance page)~~

* 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>

* 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>

* 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>

== Technical Details ==

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| 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>

|}

*

~~== System Architecture at a Glance ==~~

* 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>

== PCB Schematics & Service Manual ==

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>

*

~~== Troubleshooting ==~~

~~Quick checks commonly applicable to a non‑modded 520ST:~~

* 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>

* 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 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 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>

== Technical Documentation ==

* 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>

* 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 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 520STE/1040STE Field Service Manual|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 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>

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* [[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>

* [[Atari 1040STE]] – 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)

@@ Line 3: / Line 3: @@
 {{Infobox computer
 | name = Atari 520ST
-| image = [[File:Atari520ST.jpg|250px]]
+| image = [[File:Atari 520ST system.jpg|250px]]
 | manufacturer = Atari Corporation
 | type = Home computer / personal computer
@@ Line 19: / Line 19: @@
 | 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]]
-| successor = [[Atari 1040ST]]
+| successor = [[Atari 1040STE]]
 }}
@@ Line 59: / Line 59: @@
 * 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>
 * 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>
+== Memory and Storage ==
+RAM organization and ROM layout
+* 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/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>
+* 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>
+* 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>
+== Sound Capabilities ==
+* 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>
+* 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>
+* 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>
 == PCB Schematics & Service Guide ==
@@ Line 74: / Line 86: @@
 * 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>
 * 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>
-== Memory and Storage ==
-RAM organization and ROM layout
-* 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/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>
-* 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>
-* 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>
-== Sound Capabilities ==
-* 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>
-* 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>
-* 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>
-== General Maintenance ==
-Basic care (brief; see dedicated maintenance page)
-* 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>
-* 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>
-* 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>
 == Technical Details ==
@@ Line 118: / Line 112: @@
 | 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>
 |}
+*
-== System Architecture at a Glance ==
-* 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>
 == PCB Schematics & Service Manual ==
 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>
+*
-== Troubleshooting ==
-Quick checks commonly applicable to a non‑modded 520ST:
-* 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>
-* 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 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 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>
 == Technical Documentation ==
 * 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>
 * 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 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 520STE/1040STE Field Service Manual|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 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>
@@ Line 142: / Line 127: @@
 * [[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>
+* [[Atari 1040STE]] – 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)