Atari 520ST
 | |
| A short-case Atari 520ST with an external floppy drive, monitor and mouse | |
| Specifications | |
|---|---|
| Manufacturer | Atari Corporation |
| Type | Home computer |
| Released | Shown January 1985 (Winter CES); on sale May 1985 in Canada and West Germany, June 1985 in Britain, July 1985 in the US |
| Discontinued | April 1986 (production) |
| Intro price | US$799 with monochrome monitor and drive, US$999 with colour monitor (July 1985); US$699 and US$899 from January 1986 |
| CPU | Motorola MC68000 at 8 MHz |
| Memory | 512 KB, sixteen 256 kbit × 1 DRAMs |
| Storage | External 3.5-inch floppy drive (SF354 single-sided or SF314 double-sided); external floppy (14-pin DIN) and hard disk (DB-19) ports |
| Display | 320 × 200 (16 of 512 colours), 640 × 200 (4 of 512), 640 × 400 monochrome |
| Sound | Yamaha YM2149 programmable sound generator, three channels |
| ROM | 16 KB boot ROM on early machines; 192 KB TOS in six 32K × 8 ROMs from February 1986 |
| Power | External linear supply: +5 V 3 A, +12 V 30 mA, −12 V 30 mA |
| OS / Firmware | TOS 1.00 with GEM, loaded from disk on early machines |
| Successor | Atari 520ST+, Atari 520STM |
The Atari 520ST is the first model of Atari Corporation's ST range: a 68000-based computer with 512 KB of RAM, built into a keyboard case with an external power supply and external floppy drive. It was shown with the 130ST at the Winter Consumer Electronics Show in Las Vegas in January 1985, went on sale in Canada and West Germany in May 1985, in Britain in June and in the United States in July, and was in volume supply from September 1985.[1] Atari stopped building it in April 1986, when the 520ST+, 260ST and 520STM took over.[1]
History
[edit | edit source]Development began in May 1984 at Tramel Technologies, under the code name RBP ("Rock Bottom Price").[1] At the January 1985 show Atari gave the 130ST (128 KB) a price of US$399 and the 520ST US$599, and said both would be available in the second quarter of 1985.[2] The 130ST was dropped in April 1985. The first machines shipped without the operating system in ROM: TOS had to be loaded from disk, because it was not yet finished when production started.[1] According to the German Atari museum, the power supply and floppy drive were made separate units because this made US type approval quicker, and Atari reckoned it saved six months.[1]
At launch in July 1985 the 520ST was sold in the US as a set, US$799 with a monochrome monitor and floppy drive and US$999 with a colour monitor; in Britain the monochrome set cost £749 and in West Germany DM 2,998.[1] Compute! reported estimates of at least 100,000 520STs sold worldwide by Christmas 1985. At the January 1986 CES Atari cut the monochrome and colour systems by US$100 to US$699 and US$899, offered the computer alone for US$399, and announced that the latest machines would ship with TOS in ROM and a television output.[3] ROM TOS was fitted from February 1986.[1]
Hardware
[edit | edit source]The 520ST and the Atari 1040ST share one chip set; Atari's service manual gives the second 512 KB bank of RAM as the most significant difference.[4] Positions below are from Atari's schematic for the 520ST/260ST board, drawing C070231; the board itself is C070243.[5][1]
| Position | Device | Function |
|---|---|---|
| U10 | Motorola MC68000, 64-pin DIP | CPU, 8 MHz |
| U12 | Glue | Address decoding, chip selects, video timing (HSYNC, VSYNC, BLANK, DE), interrupt priority, bus arbitration and bus error; divides 8 MHz to 2 MHz and 500 kHz |
| U15 | Memory controller (MMU) | DRAM addressing and refresh, loads the Shifter, DMA addressing |
| – | Video Shifter | 16 palette registers, RGB and monochrome output; divides its 32 MHz crystal to 16 MHz |
| U1 | DMA controller | Floppy and hard disk DMA |
| – | Western Digital WD1772 | Floppy disk controller |
| U11 | Motorola MC68901 MFP | Interrupts, timers, RS-232 serial; 2.4576 MHz crystal Y1 |
| U20, U21 | Motorola MC6850 ACIA | MIDI and keyboard serial links |
| U19 | Yamaha YM2149 | Sound, printer data and strobe, floppy drive and side select, RS-232 RTS and DTR |
| U2–U7 | ROM sockets (28-pin) | Two 8K × 8 boot ROMs on early machines; six 32K × 8 TOS ROMs later |
Atari's museum lists the custom chips found in these machines as Shifter C025914 or C301712, memory controller C025912, C100109 or C100601, Glue C025915, C070714 or C101602, and DMA controller C025913 or C100110.[1] The keyboard assembly carries its own processor, a 1 MHz Hitachi HD6301, which scans the keys, reads the mouse and joysticks, and keeps the time of day.[4]
Memory and ROM
[edit | edit source]RAM is sixteen 256 kbit × 1 DRAMs in one 512 KB bank; the memory controller can address up to 4 MB.[4] Current machines in 1987 held TOS in six 32K × 8 ROMs (192 KB), paired high and low as U4/U7 at $FC0000, U3/U6 at $FD0000 and U2/U5 at $FE0000. Early 520STs have only two 8K × 8 boot ROMs (16 KB) and load TOS from disk into RAM; even with ROM TOS, a system disk in the drive at power-on loads its own copy.[4] The German Atari museum gives the factory TOS versions as TOS 1.00 on disk dated 20 June 1985 (only the earliest 520STs) and 20 November 1985, then TOS 1.00 in ROM dated 6 February 1986 and TOS 1.02 dated 22 April 1987.[1]
Clocks, video and sound
[edit | edit source]The Shifter's crystal is 32.0424 MHz on NTSC boards and 32.084988 MHz on PAL boards. It divides this to 16 MHz for the memory controller, which supplies 8 MHz to the CPU, Glue, DMA controller and WD1772 and 4 MHz to the MFP.[4][5] The three display modes are 320 × 200 with 16 colours and 640 × 200 with 4 colours, each from a palette of 512, and 640 × 400 monochrome, which needs a monochrome monitor such as the SM124.[4] A monochrome monitor pulls the MONOMON line low, and the CPU reads it through the MFP at power-up to choose the mode.[4] The YM2149 is clocked at 2 MHz and its three channels are mixed to the monitor speaker.[4] On the 520ST board the sound leaves through a single 2N3904 emitter follower, Q1, and a 47 µF coupling capacitor, C33.[5]
Ports
[edit | edit source]The back panel carries, from left to right, the reset button, power switch, DC power input, MIDI out and in, the television output and channel switch (on machines with a modulator), monitor, printer, RS-232 (modem), floppy disk and hard disk connectors. The cartridge slot is on the left side and the two joystick and mouse ports are on the right side.[4]
| Connector | Type | Notes |
|---|---|---|
| Monitor | 13-pin DIN | RGB, monochrome, composite (modulator machines only), audio in and out, +12 V pull-up |
| Printer | DB-25 female | Centronics-type; data and strobe from the YM2149, BUSY read by the MFP; load on the data lines no more than 2.3 mA |
| Modem | DB-25 male | RS-232C, 50 to 19,200 bit/s; 1488 driver and 1489 receiver on ±12 V |
| Floppy disk | 14-pin DIN | Second drive; up to two single- or double-sided drives in total |
| Hard disk | DB-19 female | DMA port for an external hard disk controller, up to 1 MB/s |
| MIDI in, MIDI out | 5-pin DIN | 31.25 kbaud current loop; MIDI out pins 1 and 3 also carry MIDI thru |
| Mouse/joystick 0, joystick 1 | DE-9 male | Pin 7 is +5 V, pin 8 ground |
| Cartridge | 40-way edge connector | Up to 128 KB of ROM |
| Power | 7-pin DIN | From the external supply[1] |
| Pin | Signal | Pin | Signal |
|---|---|---|---|
| 1 | Audio out | 8 | +12 V pull-up |
| 2 | Composite video | 9 | Horizontal sync |
| 3 | General purpose output | 10 | Blue |
| 4 | Monochrome detect | 11 | Monochrome |
| 5 | Audio in | 12 | Vertical sync |
| 6 | Green | 13 | Ground |
| 7 | Red |
Atari specifies the monitor signals as: sync TTL level, negative, 3.3 kΩ; monochrome 1.0 V peak to peak into 75 Ω; red, green and blue 0 to 1.0 V peak to peak into 75 Ω; audio 1 V peak to peak into 1 kΩ.[4] The German Atari museum notes that the 260ST and 520ST+ carry composite sync on pin 2.[1]
Power supply
[edit | edit source]The 520ST runs from a separate linear supply that provides regulated +5 V, +12 V and −12 V, with no adjustments. Atari rates it at 3 A on +5 V and 30 mA on each 12 V rail, 36 W maximum input. Typical demand in the machine is 1.5 A at +5 V; the 12 V rails draw 3 mA with RS-232 idle, rising to 19 mA on +12 V and 18 mA on −12 V when it is active. The supply opens by removing the four rubber feet and the four screws beneath them.[4] The German Atari museum identifies it as the PS31.[1]
On the main board the three rails enter at J9 through a filter block, L3. The power switch SW1 breaks only the +5 V line, so the ±12 V rails stay live on the board while the supply is plugged in and the switch is off. The main +5 V reservoir after the switch is C106, 470 µF.[5]
Servicing
[edit | edit source]To open the machine, turn it over and remove the six screws in the bottom case (the longer ones go at the back), lift off the top case and unplug the keyboard at the right front of the board. Three screws along the front edge and three at the rear, reached through holes in the shield, hold the board. The top shield is held by ten twist tabs.[4]
Atari's procedure for a machine with no display is to connect a terminal to the RS-232 port at 9600 bit/s, 8 data bits, 1 stop bit, no parity, and run the diagnostic cartridge, which reports through the serial port as well as the screen. If nothing appears there either, check the 8 MHz clock at 68000 pin 15, HALT at pin 17 (should be a TTL high) and BERR at pin 22 (should stay high); a CPU too hot to touch for more than a second is usually bad.[4] Atari's symptom checklist gives a black screen as no power, Glue or Shifter; a white screen as Shifter, Glue, memory controller, DMA controller or 68000; dots or bars as RAM, memory controller or Shifter; and one missing colour as the video summer, buffer or Shifter.[4]
Documentation
[edit | edit source]- Atari 520ST and 1040ST Computer Field Service Manual: Atari's service manual C026118-002 Rev B (3.6), January 1987, covering the 520ST, 520STM, 1040STF and 1040STFM.[4]
- Atari 520ST/260ST schematic C070231, three sheets, revision M (April 1986).[5]
- Atari ST Engineering Hardware Specification: Atari's hardware specification of 7 January 1986, with the memory map, register descriptions and port signals.[6]
Related pages
[edit | edit source]References
[edit | edit source]- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 "Atari 520ST, 260ST, 520ST+, 520STM, 130ST und ST Junior", atari-computermuseum.de (in German), revised 26 June 2024. Secondary source for the development code name, show and sale dates, prices, the end of production, the C070243 board, the custom chip part numbers, the TOS versions, the PS31 supply and the monitor pin 2 change.
- ↑ Tom R. Halfhill, "The Next Generation: New Computers at the Winter Consumer Electronics Show", Compute! issue 59, April 1985, p. 25. Source for the 130ST and 520ST prices announced at the January 1985 show.
- ↑ "A Turning Point for Atari? Report from the Winter Consumer Electronics Show", Compute! issue 71, April 1986, p. 30. Source for the sales estimate, the January 1986 price cuts, the separate prices and the change to ROM TOS and a television output.
- ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 4.13 4.14 Atari Corporation, 520ST/1040ST Computer Field Service Manual, part number C026118-002 Rev B (3.6), January 1987 (Mauritron copy). Section 1 (models, back panel, power supplies, pp. 1.1–1.6), section 2 (theory of operation, memory and ROM map, video, sound, port pin assignments, figures 1.4 to 1.10, pp. 2.1–2.14), section 3 ("Troubleshooting a dead unit", pp. 3.2–3.3), section 4 (520ST disassembly, pp. 4.3–4.4), section 5 (symptom checklist, p. 5.1) and the system clock diagram in section 8. Hosted on this wiki: Atari 520ST and 1040ST Computer Field Service Manual (PDF).
- ↑ 5.0 5.1 5.2 5.3 5.4 Atari (Japan) Corporation, Schematic Diagram (520ST/260ST), drawing C070231, sheets 1–3, revision M (ECO 00225, 22 April 1986). Sheet 1 for the power input J9, SW1, C106, U1, U11, U19–U21 and the audio output; sheet 2 for U10, U12, U15 and the ROM sockets U2–U7; sheet 3 for the crystal reference table (NTSC Y2 32.0424 MHz, PAL Y2 32.084988 MHz). Hosted on this wiki: File:Atari 520ST Schematic C070231.pdf.
- ↑ Atari Corporation, Engineering Hardware Specification of the Atari ST Computer System, 7 January 1986. Hosted on this wiki: Atari ST Engineering Hardware Specification (PDF).