Editing Atari 520STFM

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{{Infobox computer
| name = Atari 520STFM
| image = [[File:Atari_520STFM.jpg|250px]]
| manufacturer = Atari Corporation
| type = Home computer / personal computer
| caption = Atari 520STFM in the "long case" design with integrated floppy drive and RF modulator
| release date = {{Start date|1986}}
| discontinued = 1990 (superseded by the [[Atari 520STE]])
| price = UK £299 (1987); US$499 (approx., varied by bundle and market)
| cpu = Motorola MC68000 @ 8 MHz
| memory = 512 KB RAM (some later units shipped with 1 MB)
| storage = Internal 3.5-inch DS/DD 720 KB floppy drive; external floppy via 14-pin DIN; external ACSI hard disks
| display = 320×200 (16 colours), 640×200 (4 colours), 640×400 (mono); RF output for television
| sound = Yamaha YM2149F (3 voices + noise)
| dimensions = 78 mm × 470 mm × 330 mm (3.1 × 18.5 × 13 in) approximately
| weight = ≈5.5 kg (12 lb)
| os = Atari TOS 1.02 / 1.04 (192 KB ROM)
| predecessor = [[Atari 520STM]]
| successor = [[Atari 520STE]]
}}

The '''Atari 520STFM''' is one of the most popular and widely sold models in the Atari ST family. The designation stands for '''520''' (512 KB RAM), '''ST''' (Sixteen/Thirty-two), '''F''' (internal Floppy drive), and '''M''' (RF Modulator). Released in 1986, it combined the features that home users needed — an integrated double-sided floppy drive and television output — in a single "long case" enclosure with an internal power supply.

The 520STFM was especially successful in the United Kingdom, where it became a popular home computer and gaming machine. Its ability to connect directly to a television set, combined with its relatively low price, made it a strong competitor to the Commodore Amiga 500.

== History ==

The original 520ST (1985) was a capable machine but required an external floppy drive and a dedicated monitor, making it expensive to set up. Atari addressed this in stages: the [[Atari 520STM|520STM]] added an RF modulator for TV output, and the 520STF added an internal floppy drive. The 520STFM combined both enhancements and was housed in a larger "long case" that also accommodated an internal switched-mode power supply.

This made the 520STFM a complete computer in one box — users only needed to connect a television set and a floppy disk to get started. The machine was sold in several bundles, often including games and productivity software, and was aggressively priced against the Amiga 500 in the UK market.

The 520STFM typically shipped with TOS 1.02 ("Mega TOS") or later TOS 1.04 ("Rainbow TOS"), both in 2-chip 192 KB ROM configurations. Some later 520STFM units were upgraded to 1 MB of RAM at the factory, competing with the 1040STFM.

The 520STFM shares the C070789-001 motherboard with the [[Atari 1040STFM]], differing only in the amount of RAM installed.

== Architecture ==

* '''CPU:''' Motorola MC68000 @ 8 MHz
* '''Architecture:''' 16/32-bit (32-bit internal, 16-bit external data bus, 24-bit address bus)
* '''RAM:''' 512 KB standard (upgradeable to 1 MB, 2.5 MB, or 4 MB with aftermarket modifications)
* '''ROM:''' 192 KB TOS 1.02 or TOS 1.04 in 2× 128 KB mask ROMs
* '''Custom ICs:''' Shifter (C025914 or later GST Shifter), GLUE (C025915 or later combined GLUE/MMU), MMU (C025912), DMA (C025913)
* '''BLiTTER:''' Not standard; some C070789 boards have an unpopulated PLCC-68 footprint for the optional BLiTTER chip (Atari C101675)

=== Major ICs ===

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{| class="wikitable"
! Function !! Part Number !! Notes
|-
| CPU || MC68000P8 / MC68000FN8 || 8 MHz
|-
| Video Shifter || C025914-38A || Pixel serialiser; later boards may use GST Shifter
|-
| GLUE || C025915-38A || Bus timing, video timing; some boards use combined GLUE
|-
| MMU || C025912-38 / C100109 || DRAM controller
|-
| DMA Controller || C025913-38 || ACSI/floppy DMA
|-
| FDC || WD1772-02-02 || Floppy disk controller; -02-02 variant common
|-
| MFP || MC68901 || Timers, interrupts, UART
|-
| ACIA (×2) || MC6850 || Keyboard/IKBD and MIDI
|-
| Sound/PIO || YM2149F || 3-voice PSG + I/O
|-
| RS-232 drivers || MC1488 / MC1489 || Serial port level conversion
|-
| RF Modulator || Internal shielded module || PAL or NTSC RF output
|}

== Connectors ==

Rear panel (left to right, typically):

* '''Power:''' IEC C14 mains inlet (internal PSU) — '''CAUTION: contains mains-voltage components'''
* '''Floppy (external):''' 14-pin DIN
* '''ACSI (Hard Disk):''' DB-19 female
* '''Serial (Modem):''' DB-25 male, RS-232C
* '''Parallel (Printer):''' DB-25 female
* '''Video/Monitor:''' 13-pin DIN (analog RGB, mono, sync, audio)
* '''RF Output:''' Phono (RCA) or coaxial connector for television

Left side:

* '''MIDI In:''' 5-pin DIN
* '''MIDI Out:''' 5-pin DIN
* '''Cartridge:''' 40-pin edge connector
* '''Reset button''' (some models)

Under keyboard:

* '''Port 0:''' DE-9 male (mouse/joystick)
* '''Port 1:''' DE-9 male (joystick)

== Display ==

* '''Low resolution:''' 320×200, 16 colours from 512-colour palette, ~50/60 Hz
* '''Medium resolution:''' 640×200, 4 colours, ~50/60 Hz
* '''High resolution (mono):''' 640×400, monochrome, ~71.2 Hz (SM124/SM125 only)

The RF modulator outputs the colour display modes for television viewing. The monochrome high-resolution mode requires a dedicated monitor and cannot be viewed via RF.

== Sound ==

* '''PSG:''' Yamaha YM2149F — 3 square-wave channels + noise, 5-bit envelope generator
* '''MIDI:''' Built-in MIDI In/Out at 31.25 kbaud
* '''Audio:''' Mono line-level on monitor DIN; also mixed into RF signal

== Internal Floppy Drive ==

The 520STFM includes an internal 3.5-inch double-sided, double-density (DS/DD) floppy drive providing 720 KB formatted capacity. The drive is connected to the WD1772 floppy disk controller via the DMA chip. Common internal drive models include:

* Epson SMD-340/360
* Citizen OSDA series
* Alps DFxx series

An external floppy drive can be connected via the 14-pin DIN port for a second drive (drive B:).

== Internal Power Supply ==

The 520STFM uses an internal switched-mode power supply (SMPS), a significant change from the external "brick" PSU of the 520ST/520STM. The internal PSU provides:

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{| class="wikitable"
! Rail !! Voltage !! Typical Current !! Purpose
|-
| +5V || 5.0V ±5% || ~2.5A || Logic, RAM, ICs
|-
| +12V || 12.0V ±10% || ~0.5A || Floppy drive motor, RS-232 drivers
|-
| −12V || −12.0V ±10% || ~0.05A || RS-232 negative rail
|}

'''WARNING:''' The internal PSU contains mains-voltage components. Capacitors may retain dangerous charge even after the machine is unplugged. Always disconnect from the mains and wait at least 5 minutes before opening the case.

== Motherboard Revisions ==

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{| class="wikitable"
! Board Number !! Notes
|-
| C070789-001 || Most common 520STFM/1040STFM board; also used in the 1040STFM with different RAM population
|-
| C103175 (Rev. D) || Later revision with some component changes
|}

== BLiTTER Upgrade ==

Some C070789-001 boards include an unpopulated PLCC-68 socket position for the Atari BLiTTER chip (C101675). When installed, the BLiTTER provides hardware-accelerated block transfer operations, improving performance in GEM desktop operations and some applications. The BLiTTER upgrade requires:

* Atari C101675 BLiTTER IC (PLCC-68)
* TOS 1.02 or later (earlier TOS versions do not support the BLiTTER)
* Soldering a socket or the chip directly to the unpopulated pads

== Known Issues ==

* '''PSU capacitor failure:''' The internal switched-mode PSU is a common failure point. Dried-out or bulging capacitors can cause instability, failure to power on, or intermittent crashes. Recapping the PSU is a recommended preventive measure.
* '''Floppy drive failure:''' The internal drive mechanism can develop worn heads, dirty head assemblies, or failed drive belts. Cleaning or replacement may be required.
* '''Keyboard membrane degradation:''' Same issue as all ST models.
* '''RF modulator quality:''' The RF output provides a soft, somewhat blurry picture typical of the era. For best display quality, use the 13-pin DIN monitor output with a dedicated monitor or an RGB-to-SCART adapter.
* '''RAM issues:''' DRAM chips can develop faults over time, causing crashes, garbled displays, or failure to boot.

== Service and Repair ==

* [[Atari ST General Maintenance]]
* [[Atari ST Troubleshooting Guide]]
* [[Atari ST Capacitor Replacement Guide]]

== Software Compatibility ==

The 520STFM ran the full ST software library. Its 512 KB RAM was sufficient for most games and many productivity applications, though some later software required 1 MB. Key software categories included:

* '''Games:''' Dungeon Master, Carrier Command, Starglider, Xenon, Populous, Captive, Stunt Car Racer
* '''Music production:''' Steinberg Pro-24, C-Lab Creator/Notator — the built-in MIDI ports made the ST the standard for music production
* '''Desktop publishing:''' Calamus, PageStream
* '''Word processing:''' 1st Word Plus, WordPerfect
* '''Programming:''' GFA BASIC, Lattice C, Mark Williams C, Devpac assembler

== See Also ==

* [[Atari 260ST]] — 256 KB entry model
* [[Atari 520ST]] — Original short-case 512 KB model
* [[Atari 520STM]] — 520ST with RF modulator only
* [[Atari 520ST+]] — 520ST with 1 MB RAM
* [[Atari 1040STF]] — 1 MB model without RF modulator
* [[Atari 1040STFM]] — 1 MB model with floppy and RF modulator
* [[Atari 520STE]] — Enhanced successor with hardware scrolling and DMA audio

== References ==
<references/>

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[[Category:Atari Systems]]