Tube (BBC Micro)

Tube (BBC Micro)

In computing, the Tube was an expansion interface and architecture on the BBC Microcomputer System which allowed the BBC Micro to communicate with a second processor, or "coprocessor".

Under the architecture the coprocessor would run user code, whilst the Micro (actingas a "host") provided certain I/O functions such as screen and storage device management. A coprocessor unit could be cold-plugged into any BBC Micro with a disk interface (whose ROM contained the necessary host code) and used immediately.


Inside the coprocessor unit a proprietary chip (the "Tube ULA", initially developed by Ferranti) interfaced between, and logically isolated, the host and coprocessor buses. This allowed the Tube to adapt to different bus architectures in the coprocessor unit. The only other components needed were a microprocessor, some RAM, a small ROM containing processor specific client code, an address decoder and a power supply.

The two processors communicated through four pairs of FIFO buffers in the Tube ULA. Console input/output, error messages, data transfers and system calls each had their own pair, one buffer for each direction. To reduce latency, the queue capacity varied between 1 and 24 bytes, depending on the buffer. Each buffer had a control and status register to monitor its state and configure the raising of interrupts.

The protocol for the use of these buffers was rigorously specified by Acorn Computers [ Acorn Application Note 004, "Tube Application Note"] ] and amounts to interprocess communication by message passing. Most interaction was asynchronous but fast block transfers were synchronous and consisted of the host blindly running a simple fetch-store loop, which defined the transfer rate. The coprocessor, which had its own clock, was synchronised by passing a dummy byte and then regulated by the relevant buffer semaphore.


Numerous coprocessors were developed for the Tube; most commonly seen was a MOS Technology 6502 processor which allowed properly written BBC Micro programs to run faster and with more memory. There was also a Zilog Z80 processor to run CP/M and a National Semiconductor 32016 processor running Panos (and unofficially a UNIX variant).

These coprocessors formed the basis of the Acorn Business Computer series, the higher end machines being repackaged BBC Micros with a coprocessor attached via the Tube. The Master Series modified the Tube, allowing one coprocessor to be fitted inside the case and another to be connected externally, though the two never ran simultaneously. An internal 6502 processor could be fitted, or an Intel 80186 based system for DOS compatibility (although in practice this was limited). [Watford Electronics,"Advanced Reference Manual for the BBC Master Series",1988]

The Tube was also used during the initial development of the ARM processor, an evaluation board being developed that again used the BBC Micro as a host system for I/O operations.

Acorn had strongly discouraged BBC Micro programmers from directly accessing system memory and hardware, favouring official API calls. [Acorn Computers Ltd, "BBC Microcomputer System User Guide", chapters 43, 46.] This was ostensibly to ensure applications could be seamlessly moved to the Tube 6502 coprocessor, since direct access from there was impossible. When a program called one of the MOS entry points, a replacement subroutine in the coprocessor's ROM passed a corresponding message to the host which carried out the operation and passed back the result. In this way an application could run identically on the host or the coprocessor. Other CPU models used a custom API, which was typically an orthogonal translation of the 6502 API into a native format.


Wikimedia Foundation. 2010.

Игры ⚽ Поможем решить контрольную работу

Look at other dictionaries:

  • BBC Micro — Der BBC Micro (Acorn BBC Microcomputer) ist ein auf dem 6502 Prozessor (2 MHz) basierender Heimcomputer der britischen Firma Acorn. Seine Verbreitung fand er ab 1981 vor allem in britischen Schulen, weil eine Sendung des BBC den Acorn als… …   Deutsch Wikipedia

  • BBC Micro — BBC Modèle A à B+128 The original BBC Micro Développeur Acorn Computers Type micro ordinateur 8 bit …   Wikipédia en Français

  • BBC Micro — Infobox computer Name = BBC Model A to Model B+128 Photo = Caption = The original BBC Micro Type = 8 bit microcomputer Developer = Acorn Computers Released = Late 1981 Discontinued = 1986 Processor = MOS Technology 6502/6512 at 2 MHz Memory = 16… …   Wikipedia

  • BBC Micro — Computador BBC Micro. El BBC Micro, conocido cariñosamente como el Beeb, fue uno de los primeros ordenadores domésticos. Fue diseñado y construido por Acorn Computers para la British Broadcasting Corporation (BBC). A principios de los años 1980,… …   Wikipedia Español

  • Acorn BBC Micro — BBC Micro Der BBC Micro ist ein auf dem 6502 Prozessor (1,8 MHz) basierender Heimcomputer der britischen Firma Acorn. Seine Verbreitung fand er ab 1981 vor allem in britischen Schulen, weil eine Sendung des BBC den Acorn als Lehrmodell nutzte.… …   Deutsch Wikipedia

  • Tube — may refer to:Electronics *vacuum tube, a component of electronics *cathode ray tube, a common component of electronics such as televisions and other displays *Tube, An expansion bus on the BBC Micro computer *Nokia 5800 Tube , A mobile phoneFood… …   Wikipedia

  • BBC Master — Infobox computer Name = BBC Master Series Photo = Type = 8 bit Microcomputer Released = Early 1986 Discontinued = 1994 Processor = MOS Technology 65SC12, optional Intel 80186 or 65C102 depending on model Memory = 128 KB 512 KB OS = Acorn MOS,… …   Wikipedia

  • BBC Cheese Wedge — A Cheese Wedge for the BBC Microcomputer was a peripheral in a box with the same profile and styling as the main computer.econd processorsThe Second Processors connected to Acorn s proprietary and trademarked Tube interface. The terminology of… …   Wikipedia

  • Video camera tube — In older video cameras, before the mid to late 1980s, a video camera tube or pickup tube was used instead of a charge coupled device (CCD) for converting an optical image into an electrical signal. Several types were in use from the 1930s to the… …   Wikipedia

  • Acorn Computers — articleissues peacock=october 2008 citecheck=october 2008 citations missing=october 2008 POV=october 2008Infobox Defunct company company name = Acorn Computers company foundation = December, 1978 defunct = November, 2000 fate = Bought by Morgan… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”