Acorn  BBC Master
Previous System
Next System

BBC Master Series

The BBC Master computer was released by Acorn Computers in 1986 as a successor to the BBC Micro, model B. The machine was built around the MOS technology 65SC12 processor. This is an enhanced CMOS version of teh nMOS-based 8-bit 6502. It uses less power than the 6502 and has an increased instruction set. Also, a few problems that existed in the 6502 were fixed with the 65C12. The BBC Master came in a few different models. One of the strengths of the architecture was that it could be expanded using a co-processor, that enabled it to run DOS Plus or the GEM graphical user interface.

The system was designed and built for the BBC as part of the push to enable computing in the British education system. The computer was backwards compatible with the BBC Micro, except for some games that used features on the BBC Micro that were not part of the standard.

BBC Master Models

The BBC Master was produced in a few variations. Not all were produced in large quantities, and some of them are hard to find.

  • Master 128 - First model of the Master series
  • Master Turbo - Featured a 65C102 co-processor @4MHz
  • Master AIV - Master Turbo with a SCSI interface and a Videodisc
  • Master ET - For use on a network, only had RGB and Econet connectors
  • Master 512 - Intel 80186 co-processor @ 10MHz to run DOS Plus and GEM
  • Master Scientific - Prototype, NS32016 co-processor @ 8MHz
  • Master Compact - Compact version of the 128

BBC Master rear ports

The BBC Master did not lack connectors, and had the following ports on the rear:
  • ECO-Net connector
  • Audio Out
  • Cassette port
  • RS 432 communications port
  • Analoge port
  • RGB Monitor connector
  • Composite Video connector
  • RF Output for TV

MOS 6502 CPU

The 6502 is an 8-bit MicroProcessor designed by MOS Technology. The team was led by Chuck Peddle and had also worked on the Motorola 6800. The 6502 is a simplified, but faster and cheaper design than the 6800.

The 6502 was introduced in 1975 and was the cheapest microprocessor on the market. Together with the Zilog Z80, the 6502 helped start the home computer revolution of the 1980s. The 6502 was used in a wide range of devices: the Atari 2600, the 8-bit Atari home computers, the Apple II, the Nintendo Entertainment System, the Commodore 64, the BBC Micro and many others. All used the 6502 or a variation of it.

The 6502 is a 1MHz design, while the 6502A is designed for 2MHz. The 6502A is 100% compatible with the original 6502.

Commodore soon bought MOS Technology, but conitnued to sell the microprocessor to competitors and licensed the design to other manufacturers.

Source: WikiPedia - MOS Technology 6502
Technical Details
Released 1986 Brand Acorn Computers Ltd. Type Acorn BBC/Acorn 8-bit Name BBC Master CPU Class CUSTOM CPU Synertek SY65SC12, optional Intel 80186 or 65C102 Memory RAM: 128kB
VRAM: 512kB
Sound Chip Texas Instruments SN76489 Sound 3 Square Wave tone generators, 1 noise generator, 16 volume levels. Display Chip Motorola 6845 Display 640x256 2 colors
320x256 4 colors
160x256 8 colors
Best Color 8 colors Best Graphics 160x256 in 8 colors Sprites none System OS Acorn MOS Storage External Tape
Related Systems
Acorn System
Acorn Business Computer
Acorn BBC/Acorn 8-bit
BBC  Master (1986)
Acorn Archimedes 300/400
Acorn New Archimedes 400s
Acorn Workstations
Acorn Archimedes 3000+
Related Media
6502 CPU
Collection of books on the 6502 and compatible CPUs
Acorn / BBC
Acorn Programs Magazine is a British publication covering news, listings, and programming advice for the BBC and Acorn computers.
Acorn User
A magazine covering the early BBC computers to later the Acorn ARM machines.
The 6502/6809 Journal
Acorn / BBC
Acorn Technical and Service Manuals
World Wide Web Links
MOS 6502 CPU Wiki Page
The 6502 is an 8-bit MicroProcessor designed by MOS Technology.