Acorn Master Turbo
 | |
| A Master Turbo showing the 65C102 co-processor start-up banner (photo: Chris Whytehead, CC BY-SA 3.0) | |
| Specifications | |
|---|---|
| Manufacturer | Acorn Computers |
| Type | Home computer: BBC Master 128 with the internal 65C102 co-processor |
| Intro price | £125 for the Turbo upgrade (1986)[1][2] |
| CPU | Host: 65C12 at 2 MHz. Co-processor: 65C102 at 4 MHz |
| Memory | Host: 128 KB. Co-processor: 64 KB |
| Storage | — |
| Display | — |
| Sound | — |
| OS / Firmware | MOS 3.20[1] |
| Model no. | Upgrade ADC06; co-processor board 0243,030 |
The BBC Master Turbo is a BBC Master 128 fitted with Acorn's internal 65C102 co-processor board, sales code ADC06. The board carries a 65C102 processor at 4 MHz, 64 KB of RAM and its own Tube interface chip, and plugs into two sockets on the Master's main board. With it fitted and enabled, the Master's own 65C12 becomes the input/output processor and the co-processor runs BASIC, other languages and the user's program.[3][1]
Acorn's 1986 price lists show the Master 128 and a separate Turbo module at £125, and Chris Whytehead records that he could not establish whether Master Turbos were assembled at the factory or upgraded by dealers and owners.[1] Wikipedia describes the card as available either with the machine or as an add-on.[2] The Master AIV used in the BBC Domesday System is a Master Turbo with a SCSI interface and the Videodisc Filing System ROM added.[2]
The rest of the machine (main board, keyboard, power supply, battery and disc interface) is a standard Master 128 and is covered by Acorn's Master series service manual and by the BBC Master 128 Maintenance Guide, BBC Master 128 Troubleshooting Guide and BBC Master 128 Capacitor Replacement Guide.[4]
Co-processor board
[edit | edit source]
| Item | Fitted |
|---|---|
| Main board | 0243,000 issue 1 (replacement; his original board was issue 2) |
| Host processor | GTE G65C512P-2 at 2 MHz |
| Host RAM and ROM | 128 KB and 128 KB |
| Disc controller | WD1770-PH, with ADFS 1.50 and DFS 2.24 |
| Host operating system | OS 3.20 |
| Econet module | 0243,020 issue 2 |
| Co-processor board | 0243,030 issue 2, serial 01-ADC06-0101403 |
| Co-processor | 65C102 at 4 MHz, 64 KB |
Source: Chris's Acorns.[1]
Chris Whytehead describes the board as carrying a Ferranti Tube ULA, the 65C102 processor and 64 KB of RAM, and gives the processor as 65SC102 on his ADC06 page and 65C102 on his Master Turbo page.[1][5] Acorn's user guide calls it a 65C102.[3]
On the host side the internal Tube is the only device on the Master's 2 MHz internal I/O bus, with its data lines connected directly to the CPU data bus. The interface carries D0 to D7, A0 to A2, the host phi2 clock, reset, an open-collector IRQ, an 8 MHz timing reference, the Tube chip select and read/write.[4] The board connects through its plugs PL1 and PL2 into sockets SK1 and SK2 on the Master main board, which Acorn's parts list gives as 12-way 0.1-inch socket housings (part 0800,482).[3][4]
| Ref | Part | Function |
|---|---|---|
| IC1 | Tube ULA | Interface between the Master (host) and the co-processor; pin 3 fed from +5 V through R1, 12 ohms 1 W |
| IC8 | 65SC102 | Processor, with X1 (16 MHz crystal), C1 and C2 (15 pF) and R2 (4.7 M 2%) |
| IC11 | 2732 | Boot ROM |
| IC14 to IC21 | HM4864P | 64 Kbit DRAMs, 64 KB in total |
| IC4, IC7 | 74LS257 | DRAM row and column address multiplexers |
| IC10 | 74LS590 | Refresh address counter |
| IC2, IC3, IC5, IC6, IC9, IC12, IC13, IC28 | 74LS02, 74LS133, 74LS00, 74LS109, 74LS20, 74LS393, 74LS73, 74LS02 | Address decoding, clock and timing logic |
| RP1 | 220 ohm resistor pack | On the Tube host data lines from PL1 |
| PL1, PL2 | 12-way plugs | "Int. Tube 1" and "Int. Tube 2", into SK1 and SK2 on the Master main board |
The drawing is a community redraw, not an Acorn document.[6] It shows no electrolytic or tantalum capacitor: the supply sheet has only 100 nF decouplers, one per IC, and the other capacitors are small ceramics (C1 to C5 and C7, 15 to 47 pF).[6] As on the external Acorn 6502 Second Processor, the Tube ULA's pin 3 is fed through a 12 ohm resistor.[6]
Only one co-processor or external second processor can be active at a time. The choice between the internal and external Tube is made in software.[4]
Memory
[edit | edit source]The co-processor's 64 KB is addressed as &0000 to &FFFF and the I/O processor's memory as &FFFF0000 to &FFFFFFFF, so that the filing systems can tell which processor a load or save address refers to. BASIC does not use these extended addresses: the ?, ! and $ operators reach only co-processor memory, and I/O processor memory has to be read and written with OSWORD calls 5 and 6.[3] In the co-processor, PAGE is &800 and HiBASIC sits at &B800 to &F7FF, leaving 44 KB for a BASIC program.[3]
The support disc carries HiBASIC, HiEDIT and BUFFER. BUFFER turns the I/O processor's RAM from &4000 to &8000 into a printer buffer of about 24 KB, which only works with a co-processor in use.[3] Chris Whytehead gives the speed gain over a plain Master 128 as about 50%.[1]
Fitting and configuration
[edit | edit source].png)
Acorn's procedure, from the user guide:[3]
- Disconnect the computer from the mains. Turn it upside down and remove the four screws marked FIX, two at the front and two at the rear. The rear screws are longer.
- Hold the case halves together, turn the computer the right way up and lift the top half straight off.
- Fit the plastic support posts from the kit into the main board in numerical order. Positions 1 to 4 are used by every co-processor; 5 and 6 are only for some. A fitted post cannot be pulled out again, so check each position before pressing it home, and make sure the base flange does not foul a component.
- Line up the pins of PL1 with SK1, the pins of PL2 with SK2, and the posts with the holes in the co-processor board. Press the board down gently until the barbs on the posts click through. Too much force damages the connectors.
- Refit the top of the case.
- Switch on. The banner still reads "Acorn MOS", because the Tube is not yet enabled.
- Type
*CONFIGURE TUBEand*CONFIGURE INTUBE, then hold CTRL and press and release BREAK. - The banner should now read "Acorn TUBE 65C102 Co-Processor".
*CONFIGURE NOTUBE disables the Tube and *CONFIGURE EXTUBE selects the external Tube connector for a separate second processor.[3] The configuration is held in the fifty bytes of battery-backed CMOS RAM in the Master's 146818 clock chip.[4] If the configuration memory has been set wrongly or corrupted, Acorn's reset is to switch on while holding R and then press CTRL F BREAK. That clears every configuration setting, so set TUBE and INTUBE again afterwards.[4] See Battery Explosion, Capacitor or Corrosion Damage for the Master's battery.
Fault finding
[edit | edit source]Acorn's service manual tells the engineer to disconnect any co-processor before starting the switch-on checks, so that a fault on the Master itself is found first.[4]
| Symptom | Probable cause | Action |
|---|---|---|
| Banner reads "Acorn MOS" with the board fitted | Tube not configured | Check with *STATUS; set *CONFIGURE TUBE and *CONFIGURE INTUBE, then CTRL BREAK[3][4]
|
| Co-processor still not recognised with the configuration correct | PL1/PL2 not mated with SK1/SK2; broken connections to the two connectors; data bus bits to the I/O controller | Reseat the board and check every connection to the two connectors. Check the two data bus connections to the I/O controller, IC15 pins 18 and 19[4] |
| Recognised, but only a cursor in the top left of the screen | Faulty co-processor, poor connector mating or a badly seated boot ROM | Try the co-processor in another Master; reseat the board and the boot ROM[4] |
| Programs that write to the screen or I/O memory directly fail | Software that pokes the I/O processor's memory or hardware from the co-processor | Run it with the Tube disabled; Acorn calls such software illegal[3][4] |
| Machine beeps and leaves the cursor at the top left whether or not the co-processor is fitted | Fault on the Master itself | Diagnose the Master 128 first. Chris Whytehead's machine behaved this way, was unchanged with the co-processor removed and with the keyboard swapped, and booted after a main board swap[1] |
The Tube section of the service manual applies the same checks as the 1 MHz bus: correct cables and connectors, READY from the I/O controller (IC15 pin 17) to the CPU (IC14 pin 2) and the peripheral bus controller (IC21 pin 11), the IC15 pin 38 to IC21 pin 5 connection, the address lines to the memory controller IC20, and the two data lines to IC15.[4]
Chris Whytehead's Master Turbo later failed with smoke from its power supply, which he replaced with the supply from a spare Master.[1] The Turbo board takes its power from the Master's supply, so check the Master's rails before blaming the co-processor; see Capacitor Failure Symptoms.
Documentation
[edit | edit source]- Acorn 65C102 Co-Processor User Guide: Acorn's fitting and user guide for the co-processor (0443,030 issue 2).
- BBC Master Series Service Manual: Acorn's service manual for the Master series (0443,004), with the internal co-processor fault finding in section 7.13.
- File:Acorn 65C102 co-processor schematic (Simon Inns redraw).pdf: Simon Inns's five-sheet redrawn schematic of the co-processor board (2019, CC BY-SA 4.0).[6]
Acorn's user guide and the Master service manual have no circuit diagram or parts list for the co-processor board itself.[3][4]
Related pages
[edit | edit source]- BBC Master 128
- BBC Master 128 Troubleshooting Guide
- Acorn 6502 Second Processor, the external Tube processor for the BBC Micro that the internal board replaced[5]
- BBC Micro Model B+
- Acorn Electron Plus 1, whose cartridge interface the Master's cartridge slots extend[2]
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Whytehead, Chris. "Master Turbo", Chris's Acorns, The Centre for Computing History (retrieved 2026-10-02). Specification of his machine (main board 0243,000 issue 1, OS 3.20, co-processor board 0243,030 issue 2, co-processor serial 01-ADC06-0101403, 65C102 at 4 MHz, 64 KB); 1986 price lists showing the Master 128 and the Turbo module at £125; "approximately 50% performance improvement"; his account of the machine failing to boot, the main board swap and the power supply failure.
- ↑ 2.0 2.1 2.2 2.3 "BBC Master", Wikipedia (retrieved 2026-10-02). Sections "Design" (internal connector for Tube co-processors; the Turbo as the first of them, with a 4 MHz 65C102 and 64 KB) and "Master Turbo" (bought with the machine or added later, £125 when introduced) and "Master AIV" (a Master Turbo with SCSI and the VFS ROM, the basis of the Domesday System).
- ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 Acorn Computers, 65C102 co-processor user guide, part no. 0443,030, issue 2, April 1986. Hosted on this wiki: Acorn 65C102 Co-Processor User Guide. What a co-processor is p. 3; figure 1 (support positions, SK1 and SK2) p. 4; dismantling and fitting pp. 5 to 6; configuration and start-up messages pp. 6 to 7; *CONFIGURE TUBE/INTUBE/EXTUBE p. 9; distinguishing between memories pp. 9 to 11; figure 2 memory map p. 8; HiBASIC, HiEDIT and the printer buffer utility pp. 11 to 13.
- ↑ 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 Acorn Computers, British Broadcasting Corporation Master Series Microcomputer Service Manual, part no. 0443,004, issue 1, April 1986. Hosted on this wiki: BBC Master Series Service Manual. Co-processors p. 12; external second processor and internal co-processor selection p. 13; 2 MHz internal I/O (the internal Tube) p. 23; real time clock, battery back-up and fifty bytes of CMOS configuration RAM pp. 21 to 22; 7.1 switch on (disconnect any co-processor) p. 32; 7.1.5 configuration reset (R held at power-on, then CTRL F BREAK) p. 34; 7.12 the Tube and 7.13 internal co-processor pp. 47 to 48; parts list item 208, 0800,482 12-way socket housings SK1 and SK2, p. 61.
- ↑ 5.0 5.1 Whytehead, Chris. "Acorn ADC06 65C102 Co-processor", Chris's Acorns, The Centre for Computing History (retrieved 2026-10-02). The internal co-processor that replaced the external 6502 second processor; a Master fitted with it was called a Master Turbo; 65SC102 at 4 MHz; runs HiBASIC, HiView and HiWordwise.
- ↑ 6.0 6.1 6.2 6.3 Inns, Simon. Acorn 65C102 Second Processor, redrawn schematic in five sheets (main, RAM, ROM, supply, logic), KiCad, revision 1.0, 2 April 2019, CC BY-SA 4.0. Hosted on this wiki: File:Acorn 65C102 co-processor schematic (Simon Inns redraw).pdf. Sheet 1: PL1, PL2, RP1, IC1 with R1 12R 1W, IC8 65SC102, X1 16 MHz, C1 and C2 15 pF, R2 4M7; sheet 2: IC14 to IC21 HM4864P, IC4 and IC7 74LS257, IC10 74LS590; sheet 3: IC11 2732; sheet 4: 100 nF decoupling, one per IC; sheet 5: logic.