BBC Master 512
 | |
 | |
| A Master 512 booting DOS Plus (photo: Chris Whytehead, CC BY-SA 3.0) | |
| Specifications | |
|---|---|
| Manufacturer | Acorn Computers Ltd |
| Type | Home and education computer: BBC Master 128 with an internal 80186 co-processor |
| Released | 1986[1] |
| Intro price | Upgrade board £499 at introduction, later £399[2] |
| CPU | Host: 65C12 at 2 MHz. Co-processor: Intel 80186 (Acorn's drawing marks it 10 MHz, with a 20 MHz crystal) |
| Memory | Host: 128 KB. Co-processor: 512 KB in sixteen 256K × 1 DRAMs |
| Storage | — |
| Display | — |
| Sound | — |
| OS / Firmware | Digital Research DOS Plus with GEM; MOS 3.20 on the host |
| Predecessor | BBC Master 128 |
| Model no. | Upgrade ADC08; co-processor board 0243,200 |
The BBC Master 512 is a BBC Master 128 fitted with Acorn's internal 80186 co-processor board. The board carries an Intel 80186, 512 KB of RAM and its own Tube interface, and runs Digital Research's DOS Plus, which Acorn advertised as compatible with MS-DOS version 2 and CP/M-86, together with the GEM desktop.[3][4] The host Master keeps all its own facilities, and the user switches between the two.[3]
Everything except the co-processor board is a standard Master 128, so its maintenance, fault finding and capacitor work follow the Master 128 guides: BBC Master 128 Maintenance Guide, BBC Master 128 Troubleshooting Guide and BBC Master 128 Capacitor Replacement Guide.
Co-processor board
[edit | edit source]
Acorn's circuit diagram for the board is drawing 0143,200/C, "80186 co-processor".[5]
| Position | Device |
|---|---|
| IC1 | Tube ULA |
| IC8 | Intel 80186, marked 10 MHz; crystal X1 20 MHz |
| IC9–IC24 | Sixteen 256K × 1 DRAMs, 150 ns (512 KB) |
| IC31, IC32 | EPROMs, low byte and high byte |
| IC2–IC7, IC25–IC30 | 74LS series logic |
The drawing marks the 80186 as a 10 MHz part with a 20 MHz crystal, which the 80186 divides by two; Wikipedia also gives 10 MHz.[5][2] Chris Whytehead's specification table for his machine gives the co-processor clock as 8 MHz.[4]
The board's polarised capacitors are C7, C8 and C9, each 100 µF 10 V on the +5 V supply, and C1, 10 µF 10 V, which sets the reset pulse for the Tube ULA.[5] These four are the only electrolytics on the board.
The board plugs into the same two sockets, SK1 and SK2, as the Turbo co-processor, on plastic support posts. Acorn's fitting instructions say positions 1 to 4 are used by every co-processor and positions 5 and 6 only by some.[6] Like any internal co-processor it is enabled with *CONFIGURE TUBE and *CONFIGURE INTUBE followed by a reset.[6]
Software
[edit | edit source]Acorn supplied DOS Plus and the GEM Desk Top, GEM Write and GEM Paint packages with the upgrade, and said a dual 80-track disc drive was needed to run programs on the 512.[3] Chris Whytehead notes that Acorn's own 512 User Guide covered GEM, and that the Dabs Press Master 512 User Guide and Master 512 Technical Guide filled in DOS Plus and the hardware. His machine came with Acorn's two-button mouse (0143,210) for GEM.[4] Wikipedia records compatibility limits with software that used IBM hardware directly or needed more than the memory left after DOS Plus, and third-party RAM expansions to 1 MB.[2]
Faults
[edit | edit source]Treat a Master 512 as a Master 128 first. Acorn's fault-finding starts by removing any co-processor, and the internal co-processor checks (configuration, connector mating, the two data bus lines to the I/O controller IC15 pins 18 and 19, boot ROMs seated) are in section 7.13 of the service manual.[7] Two further points:
- The four electrolytics can be replaced like for like; see BBC Master 128 Capacitor Replacement Guide#Co-processor boards.
- One owner traced a dead keyboard and a constant tone on a Master 512 to the host's 146818 clock chip (IC11) pulling the slow data bus line SA0 low after battery leakage near PL8; replacing IC11 cured it. That fault is on the Master board, not the co-processor.[8]
Documentation
[edit | edit source]- BBC Master Series Documentation: the 80186 co-processor circuit diagram and Acorn's leaflet APP110.
- BBC Master Series Service Manual: the host machine.
Related pages
[edit | edit source]- BBC Master 128
- Acorn Master Turbo
- BBC Master 128 Maintenance Guide
- BBC Master 128 Troubleshooting Guide
- BBC Master 128 Capacitor Replacement Guide
References
[edit | edit source]- ↑ Whytehead, Chris. "Master Computers", Chris's Acorns (retrieved 2026-10-02). At the Master series launch in January 1986 Acorn advertised the Master 128, Master Turbo, Master 512 and Master Scientific.
- ↑ 2.0 2.1 2.2 "BBC Master", Wikipedia (retrieved 2026-10-02). Section "Master 512": 10 MHz 80186 and 512 KB; DOS Plus and GEM; upgrade introduced at £499, later £399, £199 plus VAT in early 1987 with GEM Desk Top, Write and Paint free, and a final cut to £99 reported in 1989; compatibility limits; third-party memory expansion to 1 MB.
- ↑ 3.0 3.1 3.2 Acorn Computers, Open up to the world of MS-DOS, leaflet APP110, 4 pages, hosted as File:Acorn Master 512 leaflet Open Up to the World of MS-DOS (APP110).pdf. The Master 512 as a Master 128 with a 512 upgrade board; Intel 80186 with 512 KB of RAM and 128 KB of ROM; DOS Plus compatible with MS-DOS version 2 and CP/M-86; GEM Desk Top, GEM Write and GEM Paint supplied free; a dual 80-track disc drive needed; dealer fitting; a VIEW text transfer program; a list of MS-DOS and CP/M programs Acorn had tested.
- ↑ 4.0 4.1 4.2 Whytehead, Chris. "Master 512", Chris's Acorns (retrieved 2026-10-02). The module at £399 including VAT; DOS Plus and GEM; the Acorn two-button mouse 0143,210; Acorn's 512 User Guide covering GEM, supplemented by the Dabs Press User and Technical guides; his machine's specification: main board 0243,000 issue 2, co-processor board 0243,200 issue 1, serial 01-ADC08-018489, 80186 at 8 MHz, 512 KB.
- ↑ 5.0 5.1 5.2 Acorn Computers, 80186 co-processor, drawing 0143,200/C, in File:Acorn BBC Master Series Technical Drawings.pdf, PDF page 6, described on BBC Master Series Documentation. IC list on the drawing (Tube IC1; 74LS132, 74LS04, 74LS20, 74LS109, 74LS08 and 74LS113 IC2 to IC7; 80186 (10 MHz) IC8; DRAM 256K × 1 150 ns IC9 to IC24; 74LS75, 74LS373 and 74LS367 IC25 to IC30; EPROM low and high byte IC31 and IC32); X1 20 MHz with C3 and C4 18 pF; C7, C8 and C9 100 µF 10 V and decouplers on +5 V; C1 10 µF 10 V with R1 47 kΩ and D1 on the Tube ULA reset; R2 12 Ω 1 W marked not fitted; links LK1 to LK5; connectors PL1 and PL2.
- ↑ 6.0 6.1 Acorn Computers, Master Series Hardware Specification, hosted as File:Acorn BBC Master Series Hardware Specification.pdf, 65C102 co-processor user guide, PDF pp. 34–37: support posts (positions 1 to 4 common to all co-processors, 5 and 6 only for some), PL1 to SK1 and PL2 to SK2, *CONFIGURE TUBE and INTUBE.
- ↑ Acorn Computers, Master Series Microcomputer Service Manual, 0443,004, 7.1 "Switch on", p. 32 (disconnect any co-processor), and 7.13 "Internal co-processor", pp. 47–48.
- ↑ stardot.org.uk, "Master 512 keyboard issues - 6522? (Solved - bad RTC)" (November–December 2024, retrieved 2026-10-02). Boydie: corrupt CMOS banner, constant background tone, many dead keys; SA0 stuck at about 0.04 V; battery leakage near PL8; cutting pin 4 of IC11 restored the keyboard and a new 146818 completed the repair. 1024MAK: SA0 also goes to IC16 pin 34, IC12 pin 10 and IC11 pin 4. Secondary source.