Acorn A680
 | |
| A680 running RISC iX and X Windows (photo: Chris's Acorns) | |
| Specifications | |
|---|---|
| Manufacturer | Acorn Computers |
| Type | Workstation (prototype technical publishing system) |
| Released | 1988 (not sold) |
| CPU | ARM2, 8 MHz clock |
| Memory | 4 MB (one MEMC) or 8 MB (two MEMCs) |
| Storage | 70 MB SCSI hard disc; 2 MB floppy drive or 40 MB cartridge tape |
| Display | 19-inch monochrome monitor, 1152 × 900 at 66 Hz |
| Sound | — |
| Power | Internal 120 W switch-mode supply |
| Dimensions | 480 × 406 × 120 mm (main unit) |
| OS / Firmware | RISC iX (Acorn UNIX) |
| Model no. | A680 |
The Acorn A680 is a UNIX workstation that Acorn built in 1988 as a prototype for a desktop publishing system to be sold by Olivetti. Acorn's own documents call it the Acorn Technical Publishing System. The system never went into production, and the remaining prototypes are very rare.[1] It runs RISC iX, Acorn's version of BSD 4.3 UNIX, and was the first machine built to run it. Acorn used A680s internally to develop RISC iX for the later R140, R225 and R260, which are based on the Archimedes.[1]
The A680 differs from an Archimedes in having no RISC OS, an on-board SCSI interface, a high-resolution monochrome monitor, a laser printer interface card and up to 8 MB of memory with two memory controllers.[1][2]
System
[edit | edit source]| Part | Specification |
|---|---|
| Computer unit | Metal case with plastic mouldings, 120 × 480 × 406 mm; main PCB, power supply, four-slot backplane, two 3.5-inch drives |
| Processor and memory | ARM with MEMC; 4 MB with one MEMC or 8 MB with a master and slave MEMC |
| Storage | 70 MB SCSI hard disc; either a 2 MB floppy drive or a 40 MB cartridge tape drive |
| Monitor | 19-inch monochrome, 1152 × 900 pixels at 66 Hz, paper-white phosphor |
| Expansion | Backplane with three 64-way podule sockets and one 96-way coprocessor socket |
| Printer | Laser beam printer expansion card driving a 300 dpi, 8 page-per-minute laser printer, or a PostScript printer on the serial port |
| External storage | Optional unit with a 280 MB hard disc or a 150 MB streaming tape, on SCSI |
| Keyboard and mouse | 101-style keyboard with a microcontroller; three-button mechanical mouse plugged into the keyboard |
| Software | Frame Technology's FrameMaker under Acorn UNIX, with NeWS, NFS and Ethernet TCP/IP |
Sources: Acorn's technical reference manual.[2][3]
Hardware
[edit | edit source]
The master MEMC generates the processor's 8 MHz two-phase clock from a 24 MHz input, which comes from an ECL 96 MHz oscillator divided by four.[2] The main board carries a 33C93A SCSI controller (IC10), an 8530 serial controller (IC18), a 9793 floppy disc controller (IC119), the PCF8583 clock and CMOS RAM (IC54), and 64 one-megabit ZIP DRAMs for the full 8 MB.[3] Chris Whytehead's A680 has main PCB 0174,000 issue 1 with an ARM3 upgrade fitted in place of the original ARM2, two MEMC1a chips and a VIDC1a, and uses the same backplane part as the A410 and A440.[1]
Power supply
[edit | edit source]The power supply is a 120 W high-frequency switching unit in an L-shaped bracket with a cover.[3]
| Rail | Voltage range | Current | Ripple and noise |
|---|---|---|---|
| +5 V | 4.95 to 5.25 V, set by a trimmer next to pin 4 on the PCB | 2 to 12 A | 50 mV RMS |
| +12 V | 11.3 to 12.7 V | 0.5 to 3 A | 100 mV RMS |
| −5 V | 4.75 to 5.25 V | 0 to 0.25 A | 50 mV RMS |
| −12 V | −11.3 to −12.7 V | 0 to 0.5 A | 200 mV RMS |
Input is 198 to 264 V AC, or 90 to 135 V selected by a link. Over-voltage protection on +5 V operates between 5.8 and 7.0 V, all outputs are protected against short circuits, and the hold-up time is at least 18 ms at full load. The output cable carries live, neutral and earth on pins 1 to 3, +5 V on pin 4, common on pins 5 and 6, +12 V on pin 7, −12 V on pin 8 and −5 V on pin 9.[3] The supply needs at least 2 A on +5 V and 0.5 A on +12 V, so test it under load.[3]
Warning: the supply works from mains voltage and contains charged capacitors after it is unplugged.
Built-in diagnostics
[edit | edit source]A hexadecimal display (IC32), visible with the lid off, shows the progress of the test software in the ROMs, so that faults can be found without a working monitor. With the processor held in reset, the display flashes on and off about every four seconds, which shows that the processor is receiving its clocks.[2]
| Code | Meaning |
|---|---|
| 1 | Failed ROM test 1 (test part of the ROM) |
| 2 | Failed ARM processor test |
| 3 | Failed quick RAM check; followed by address, expected data, found data |
| 4 | Failed ROM test 2 (full CRC of the ROM) |
| 5 | Failed normal RAM test; followed by address, expected and found data |
| 6 | Failed normal MEMC CAM mapping or protection tests |
| 7 | Coprocessor failure or undefined instruction failure |
| 8 | Failed full RAM test; followed by address, expected and found data |
| 9 | Failed full MEMC CAM mapping or protection tests |
| A | Failed parallel port loopback tests; a solid A means the whole I/O system is suspect (A0 busy/strobe, A1 control/status, A2 data, A3 interrupt) |
| B | Flashing: waiting for the test station; steady: in cooperative test with it |
| D | Unexpected abort, followed by the abort type and R14 |
| E | Boot started but not finished |
| F | Entered a language; all correct |
Codes 0 and C should never appear.[2] Adrian Godwin reported faulty segments on the display of the A680 he sold, so check the segments before trusting a reading.[1]
Clock battery
[edit | edit source]The PCF8583 clock and CMOS RAM are backed by a two-cell dry battery, which can be changed with the machine switched on without losing the data. D7 stops the 5 V rail charging the battery, D8 stops the battery discharging into the power supply, and the battery voltage can be measured at TP3, which must not be shorted to 0 V.[2][3] Dry cells leak with age; remove them from a stored machine. See Battery Explosion, Capacitor or Corrosion Damage.
Capacitors and fuses
[edit | edit source]The main PCB parts list gives two types of aluminium electrolytic:[3]
| Value | Type | Acorn part | Designators | Qty |
|---|---|---|---|---|
| 10 µF 16 V | Radial | 0635,100 | C38, C40, C42 to C44, C46 to C48, C57, C69, C74, C79, C80 to C82, and eight positions marked "B" | 24 |
| 220 µF 16 V, 20 % | Radial | 0635,227 | C62, C66, C67, C72 | 4 |
The positions named for the 10 µF part add up to 23 against the quantity of 24. The rest of the board's capacitors are ceramics and decouplers, with C70, C75, C77 and C78 listed as "MPSTR" film types.[3] The board has two fuses: F1, protecting the SCSI terminator power (500 mA in the parts list, 1 A in the SCSI chapter), and F2, a 2 A fuse in the keyboard's 5 V supply.[2][3]
Links
[edit | edit source]LK17 enables the reset key on the keyboard and is normally left out, because a UNIX system should only be reset after shutting down. LK14 holds the system in reset. LK9 is fitted only on a 4 MB machine, and LK6 and LK7 set the clock phase between the master and slave MEMCs on an 8 MB machine.[2][3]
Surviving machines
[edit | edit source]Chris Whytehead's A680, serial number 147, was bought from Adrian Godwin in 2005 and came with the hardware technical reference manual, which Chris scanned. Godwin listed the changes and faults on it when he sold it: an ARM3 upgrade, a Conner 100 MB disc in place of the failed Rodime 67 MB, extra wiring for a VGA monitor, some unreliable keys, faulty segments on the LED display, and a mains switch, a standard TV part, that had been bypassed.[1] The A680 normally drives a high-resolution monochrome monitor; Chris Whytehead found it worked with an Acorn AKF90 using the green input only.[1]
The A680 user guide, programmer's reference manual and service manual are not known to survive online.[1]
Documentation
[edit | edit source]- Acorn A680 Technical Reference Manual: Acorn's hardware reference in two parts, with the circuit diagrams, assembly drawings and podule drawings.
Related pages
[edit | edit source]References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Whytehead, Chris. "RISC iX Computers: A680", Chris's Acorns, The Centre for Computing History (retrieved 2026-10-01). Includes Adrian Godwin's description of the A680 he sold in 2005 (serial 147): built in 1988 as a prototype for a publishing system to be sold by Olivetti; never put into production; the first machine built to run RISC iX and used at Acorn until spare R260s were available; ARM2 replaced by an ARM3, Rodime 67 MB disc replaced by a Conner 100 MB; unreliable keys, faulty segments on the internal LED display, an unreliable mains switch (a standard TV part) that had been bypassed. Chris Whytehead's specification: main PCB 0174,000 issue 1, Watford Electronics ARM3 at 25 MHz, two MEMC1a, 8 MB, VIDC1a, Sony MP-F17W-60D floppy drive, on-board SCSI, backplane 0283,040, RISC iX 1.21c; podules: Acorn Lance Ethernet, laser printer interface, AKA30 SCSI. Works with an AKF90 monitor using green only.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 Acorn Computers, Acorn Technical Publishing System Technical Reference Manual, part no. 0474,905, issue B, July 1988, part 1. Hosted on this wiki: Acorn A680 Technical Reference Manual. Product overview pp. 1 to 4; main PCB overview pp. 5 and 6; processor and memory pp. 9 to 22 (8 MHz clocks from the master MEMC, 4 or 8 MB); hexadecimal display and test ROM diagnostics pp. 23, 24; reset and keyboard fuse F2 p. 38; clock/RAM and battery p. 55; SCSI terminator fuse F1 p. 76.
- ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 Acorn Computers, Acorn Technical Publishing System Technical Reference Manual, part 2. Hosted on this wiki: Acorn A680 Technical Reference Manual. Power supply unit pp. 159 to 162; PCB links and test points pp. 231, 232; main PCB parts list pp. 235 to 246; mechanical specification p. 263.