Acorn BBC Micro Model B

In 1980s British education authorities decided to introduce some computer science teaching project. In the Computer Literacy project IT teaching has been standardised to use single, British computer types (Acorn, Sinclair and Dragon computers were considered, but finally Acorns have been chosen), unified teaching program. BBC produced a TV series popularizing usage of microcomputers. In their popularity peak, about 80% schools had BBC computers.
Acorn BBC Micro was Acorn's computer for schoold, but it could be ordered for private use too. Inside, it had 32kB of RAM (Model A had 16kB) and 6502 CPU usually made by Rockwell. The machine had more I/O ports than other British computers: Not only 1MHz bus expansion, but also "Tube" bus, allowing to connect other processors to the computer. Tube allows to connect second 6502 for graphics application or ARM processor. BBC Micros equipped with ARM were used as development kits for later Acorn ARM computers. Connecting Z80 to Tube could make BBC Micro run CP/M programs.
For usage in schools Acorn used a low-cost, serial port based (RS422)  local area network called Econet. Not all BBC Micros had Econet electronics installed, and installation of needed components sometimes requires to replace ROM.
Some rare BBC Micro have TMS5220+TMS6100 chips installed. These chips allow to synthesize speech.
BBC Micro, called "Beeb" was very popular and in UK it's still popular in hobbyist's workshops. Still (2015) there are many Internet pages about it and they are usually still maintained.

Manufacturer Acorn

Origin UK
Year of unit 1984?
Year of introduction 1982
End of production ???
CPU MOS 6502
Speed 1.8MHz
ROM Depends on user, usually ca. 32kB
Colors: Maximum 16
Sound: 3 channels
Display modes: Text: 40x25 (teletext), 20x32, 40x25, 40x32, 80x32, 80x25
Graphics: 160x256x16 colors, 320x256x4 colors, 640x256x4 colors.


Media: Tape, disk drive,
ROM expansions.

Power supply:

Built-in switching power supply

I/O: System bus,
1MHz Bus
TUBE expansion
FDD connector
User port
Printer port
RF out, RGB out, composite out
Cassette port
Analog joystick input
Econet local network
Possible upgrades: Many expansions using 1MHz bus, Tube bus or serial/parallel ports.
Software accessibility: Quite easy (TOSEC, sites)  

My unit probably comes from school, because it has a complete Econet set on board. It has also connector for Solidisk expansion card (but no board fitted). Solidisk was a board which was inserted into edge connector installed into one of ROM sockets. Because ROM sockets don't provide all CPU signals, it was needed to connect few wires soldering them directly to chips. The Solidisk expansion card provided two ROM sockets and additional 32K of memory.
My unit has also additional ROM with Edword text editing software.

Now about British plugs.
Until 1992 British home electric devices were sold without mains plug. If your house had European sockets, you installed European plug. If, like most houses in UK, you had British sockets, you installed British standard (Type G) plug. These plugs were available even in normal stores all over country.
In BBC Micro you may see that the plug is not manually mounted - it's a plastic moulded plug on a cable. The legal requirement to supply devices without plug was in order with home-use devices. BBC Micro computers were made under specification for British education, where British sockets were (and still are) in use. National orders were exceptions of this rule.

If your BBC has problem with starting, check power supply and its capacitors. 230V filtering capacitors and electrolytic ones may be damaged, as they may leak after long time.

Contents: Starting, usage Recording media Pinouts Links


The machine just boots up to Acorn BASIC or, depending on configuration, contents of some ROM. Versions with ECONET network support may display its number and "no clock" which maens that there is no network connected (Econet was quite similar to Polish Junet, but Acorn used better cables and more reliable transmission). BASIC is quite conventional, but is has a few significant features. Except Basic commands there are * comands, starting with character *. These commands address the ROM directly. The most important are:
*TAPE - switches tape as the main storage. In the opposite is *DISC.
*SAVE, *LOAD - saves and loads machine-code software from main storage.
*[name] - Starts [name] program from ROM.

In BASIC, you can load and save BASIC programs using LOAD "program" and SAVE "program" commands.
Before running program from ROM, make sure that you have set a proper main storage. If you try to run program from ROM with DISC storage while there is no disk drive present, it will not work properly.





Recording media

See Acorn BBC Master, as it has similar disk system (DFS, not ADFS!)




Important Pinouts:

RGB Pinout:

1 - Red
2 - Green
3 - Blue
4 - Sync
5 - GND
6 - +5V


Tape connector:

1,4 - Output
2 - GND
3 - Input
5 - N.C.


1 - CtS
2 - RtS
3 - GND
4 - Data in
5 - Data out


1 - Data+
2 - GND
3 - Clock+
4 - Data-
5 - Clock-


More pinouts can be found in this document.




Links: - BBC Micro user's guide - Link settings - BASIC commands - Expansion, which in part is presented in this page - Nice mainboard photo - File archive, many technical manuals and programs - Everything related to Acorn - Which floppy driver work with BBC? - Hardware faults symptoms and how to fix them - Games for download! - Disk images, software, ROMs - He has a big ROM archive, cover sacne and technical descriptions - How about an emulator? ;)

You can also watch the original Computer Programme from BBC Television.