BBC Master
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2008-07-07T17:08:15Z
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{{ Infobox computer
| Name = BBC Master Series
| Photo = [[Image:Acorn front.jpg|300px|thumb|Acorn's BBC Master.]]
| Logo = <!-- Deleted image removed: [[Image:Bbc-master-logo.jpg]] -->
| Type = [[8-bit]] [[Microcomputer]]
| Released = Early 1986
| Discontinued = 1994
| Processor = [[MOS Technology 6502|MOS Technology 65SC12]], optional [[Intel 80186]]
| Memory = 128 [[kilobyte|KB]] - 512 KB
| OS = [[Acorn MOS]], optional [[DOS Plus]]
}}
The '''BBC Master''' was a home computer released by [[Acorn Computers Ltd|Acorn Computers]] in early [[1986]]. It was designed and built for the [[British Broadcasting Corporation]] (BBC) and was the successor to the [[BBC Micro|BBC Micro Model B]].
The Master featured several improvements on its predecessor. The systems had 128 [[kilobyte|KB]] RAM as standard, alleviating the shortage of available RAM which had amongst other things discouraged use of the best graphics modes in the original design, and had two cartridge slots mounted above the new numerical keypad. Rather than the [[MOS Technology 6502]] [[Central processing unit|microprocessor]] used by the [[BBC Micro|Model B]] it ran on the slightly improved [[WDC 65C02|65SC12]]<ref>As shown on pictures of the Master 128 motherboard http://www.bbcmicro.net/old-8bs/insides.htm#m128</ref>: the cost of this CPU compatibility with the Model B was that the address bus was still only 16 bits, meaning that only 64 KB could be directly addressed at any one time and the remaining memory had to be paged in as required. However the 65SC12's extra instructions allowed a little more to be shoehorned into the OS and BBC BASIC ROMs, limited by the memory architecture to 16 KB each.
Although the Master was intended to be compatible with "legally written" software for the older models, there were some problems running older programs, particularly games. Conversely, although few programs were ever targeted specifically at Master series machines (except the Master 512), many later BBC games (and Master versions of earlier classics such as ''[[Elite (computer game)|Elite]]'') included enhanced features which took advantage of the extra memory.
==Models==
[[Image:BBC owl.svg|right|thumb|The BBC Computer Literacy Project Owl appeared on the bottom left of the keyboard on both standard and Master Compact cases.]]
The Master was available in several different models.
===Master 128===
This was the standard issue computer. The 128 in the name referred to its 128 KB of [[random access memory|RAM]], though it also featured 128 KB [[Read-only memory|ROM]].
===Master Turbo===
This was a Master with 4 MHz [[WDC 65C02|65C102]] second processor card (which could be either bought with the machine or added to an existing Master 128).
===Master AIV===
The Master AIV (Advanced Interactive Videodisc) was essentially a Master Turbo model with a [[SCSI]] interface and a VFS (Videodisc Filing System) [[Read-only memory|ROM]] added, and formed the basis of the [[BBC Domesday Project|BBC Domesday System]]. Although normally supplied as part of a Domesday System, with [[Laserdisc|LaserVision]] player, Domesday [[videodisc]]s, monitor and [[trackball|trackerball]] included, an upgrade kit was also available to turn a normal BBC Master into a Domesday System.
===Master ET===
The ET (Econet Terminal) system was designed for use in a network and as such had no interfaces except [[RGB]] and [[Composite video]], plus an [[Econet]] interface module and ANFS fitted as standard (it was usually an option). It used the same main circuit board as the Master 128, but the components for missing interfaces were simply not fitted (though there was nothing stopping them being added later by someone with appropriate soldering skills). The internal [[Read-only memory|ROM]] also contained much less software than that of the Master 128.
===Master 512===
This system boasted a second processor card with a 10 MHz [[Intel 80186]] and 512 KB memory. It also had the ability to run [[DOS Plus|DOS+]] and the [[Graphical Environment Manager|GEM]] graphical user interface.
===Master Compact===
[[Image:BBB MC GUI 2.jpg|thumb|right|200px|The Master Compact GUI]]
This model separated the keyboard from another unit which could be placed under the monitor. Only the [[Advanced Disk Filing System|ADFS]] filing system was supplied as standard, though it is possible to load a 1770 DFS ROM into sideways RAM, or to insert a ROM or EPROM containing it. The Master Compact also utilised a limited re-burn EEPROM, instead of the battery backed CMOS memory found in the other models.
The unit under the monitor housed a 3½” [[floppy disk]] drive and the system power supply. The remainder of the system was housed in the same unit as the keyboard, much like a conventional Master 128. The cartridge and cassette ports were removed as a space saving measure. The loss of the latter was a move Acorn later came to regret. Software for the Compact became very expensive (typically £20 for a game) due to the much lower demand for the 3½” disk format (5¼" was the de facto standard for the Master and earlier BBC Micro).
The Compact included Acorn's first public GUI. Little commercial software, beyond that included on the Welcome disk, was ever made available for the system.
<!-- FAIR USE of BBB_MC_GUI_2.jpg: see image description page at http://en.wikipedia.org/wiki/Image:BBB_MC_GUI_2.jpg for rationale -->
== Notable applications ==
The BBC Master Turbo was the basic hardware platform required to run the 1986 [[BBC Domesday Project]]. Also required were a [[SCSI]] interface and [[videodisc]] player, both of which were designed specifically for this application.
== Specifications ==
*2 [[megahertz|MHz]] [[Rockwell]] [[WDC 65C02|R65SC12]] processor
*128 KB [[Read-only memory|ROM]], consisting of 16 KB MOS (Machine Operating System), always accessible, and seven 16 KB ROMs, any one of which could be paged into memory at a time:
**16 KB [[BBC BASIC programming language|BBC BASIC]]
**16 KB [[Disk Filing System]]
**16 KB [[Advanced Disk Filing System]]
**16 KB [[Acornsoft View]] (word processor)
**16 KB [[ViewSheet]] (spreadsheet)
**16 KB Acorn Screen Editor AKA Edit (text/BBC BASIC editor)
**16 KB MOS extras (such as the cassette filing system)
*128 KB [[Random Access Memory|RAM]], comprising:
**32 KB main user program/data storage
**20 KB "[[Shadow RAM (Acorn)|shadow]]" video memory (paged over main user RAM)
**12 KB OS workspace (paged over main user RAM)
**64 KB workspace accessible to user machine code applications (in four 16 KB "[[Sideways address space|Sideways]]" blocks any one of which could be paged into memory if BBC BASIC and the other paged ROMs were not required)
*Full-travel [[computer keyboard|keyboard]] with a top row of ten red-orange [[function key]]s <math>f_0-f_9</math> and [[PC AT|AT]]-style numeric keypad
*Highly configurable graphics display based on the [[Motorola 6845]]. Unlike on the original [[BBC Micro]], separate video RAM was used so that choosing a high-resolution mode did not reduce the amount of available user RAM. (However, user RAM could still be used as the video buffer if required, in order to allow effects such as [[double buffering]].) Eight graphics modes were provided by the system ROM:
**Modes 0 to 6 could display a choice of colours from a logical palette of sixteen, though only eight physical colours could really be generated by the hardware; the eight [[RGB]] colours (black, red, green, yellow, blue, magenta, cyan, white) and said colours in a flashing state;
**[[Image:MODE 6 Master Series.png|thumb|right|Screen mode 6 with a blue background, showing the filler lines]] Modes 3 and 6 were special software (framebuffer) text modes. To save RAM, the count of lines was reduced from 32 to 25. As this would reduce the height of the frame, filler rows were created between each line of text when the frame was output, where no pixels were read from the framebuffer. This creates characteristic black lines between the rows of text when a different background colour is set, and a blank gap at the bottom of the display with the left-over pixels. The screen mode is otherwise held in memory as a regular graphics mode.
**Mode 7's [[Teletext]] capability was provided by a [[Mullard]] SAA5050 Teletext chip.
{{BBC modes}}
*Four independent sound channels (one noise and 3 melodic) using the [[Texas Instruments SN76489]] [[sound chip]]
*Built-in hardware support included:
**pluggable ROMs, directly or via cartridge slots
**[[floppy disk]] drives (both [[Disc Filing System|DFS]] and the newer [[Advanced Disk Filing System|ADFS]] supported) with [[WD1771|WD1770]] disk controller
**[[compact audio cassette|tape]] interface (with motor control), using a variation of the [[Kansas City standard]] data encoding scheme
**[[Centronics]] parallel printer
**serial communication (using [[RS-423]], a superset of [[RS-232]])
**display output for TV, RGB or 1v p-p video monitor
** A 15 pin 'D shaped' port with four analogue inputs (suitable for two [[joystick]]s, four digital/contact ports (for buttons) and a special [[Light pen]] input, and
**proprietary "Tube" interface for internal or external second CPU (in the Master 512 model, an [[80186]] was used; other options included a 3 MHz extra [[MOS Technology 6502|6502]], a [[Zilog Z80]] for e.g. [[CP/M operating system|CP/M]], an [[NS32016]], an [[ARM architecture|ARM1]], and others)
**a 16 pin IDC style "user port" consisting of 8 general purpose digital I/O pins (and two special ones) mapped directly into the 6502 via, and
**generic expansion through the "1 MHz bus".
**[[Econet]] interface, installed by adding a module board and the ANFS ROM.
Several of the inputs were directly wired to specific registers in order to allow the hardware to do some of the heavy lifting. For example the light-pen input would directly halt a counter which was started by the start of the vertical sweep of each display refresh, making calculation of where the lightpen was touching the screen little more than a simple divide/remainder operation. Likewise, the motor control relay for the audio cassette tape was controlled by a simple command and could be readily used in numerous applications.
==References==
{{reflist}}
{{Acorn_computers}}
{{BBC Computer Literacy Project}}
[[Category:Acorn Computers]]
[[Category:Home computers]]
[[Category:BBC|Master]]
[[nn:BBC Master]]
[[pt:BBC Master]]
[[sv:BBC Master]]