BBC Microcomputer System Information Sheet G2
BBC Microcomputer System Information Sheet G2
BBC Microcomputer System Information Sheet G2
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<strong>BBC</strong> <strong>Microcomputer</strong><br />
<strong>System</strong>
<strong>BBC</strong> <strong>Microcomputer</strong> <strong>System</strong> Plan<br />
*Options requiring additional<br />
hardware within <strong>BBC</strong> <strong>Microcomputer</strong>
■ Processor 2 MHz 6502A<br />
■ Memory 16K ROM BASIC<br />
16K ROM Machine Operating <strong>System</strong><br />
32K RAM (16K on Model A)<br />
■ Keyboard 73 key full OWERTY layout, including 10 user definable<br />
function keys, 4 cursor control keys, two key rollover<br />
and auto repeat.<br />
■ Display Mixed high resolution graphics and upper and lower<br />
case text.<br />
Full colour on all 8 display modes:<br />
0 640x 256 2 colour graphics and 80x 32 text<br />
1 320x 256 4 colour graphics and 40 x32 text<br />
2 160 x 256 16 colour graphics and 20 x 32 text<br />
3 80 x25 2 colour text<br />
4 320x256 2 colour graphics and 40x32 text<br />
5 160x256 4 colour graphics and 20x32 text<br />
6 40 x25 2 colour text<br />
7 40x25 Teletext display<br />
UHF, composite video and separate RGB and Sync<br />
outputs.<br />
■ External Storage 300 baud and 1200 baud interface (with motor control)<br />
for standard cassette recorders.<br />
■ Tone Generation Three-voice music synthesis with full envelope control<br />
feeding internal loudspeaker.<br />
■ Printer Interfaces 1 8 bit plus full two-line handshake "Centronics" port.<br />
(Model B Only) 2 75 baud to 9600 baud software selectable serial<br />
port to drive RS232 devices with full two-line<br />
handshake.<br />
■ User Input/Output 8 bit parallel input/output port.<br />
(Model B Only)<br />
■ Analogue Inputs Four analogue inputs for games, paddles or control<br />
(Model B Only) applications.<br />
■ Expansion Within the computer (at extra cost)<br />
Capabilities Floppy Disk Interface<br />
Econet Interface<br />
Speech Synthesis<br />
Cartridge ROM Pack Interface<br />
"Tube" connector for second processor option.<br />
■ Second Processor The Computer is designed so that it can be expanded<br />
Option to run with a second processor and considerably<br />
expanded memory.<br />
Planned expansion units which are connected via the<br />
"tube" include:<br />
3 MHz 6502 with 60K RAM<br />
Z80 with 60K RAM running CP/M<br />
16 bit processor with 128K RAM.<br />
3
Model A <strong>BBC</strong> <strong>Microcomputer</strong> <strong>System</strong><br />
A fast, powerful self-contained computer system generating high resolution<br />
colour graphics and capable of synthesising 3 part music. The computer is<br />
contained in a rigid injection moulded thermoplastic case. The following are<br />
contained within the computer thus ensuring the minimum of connecting wires.<br />
■ 73 key full travel QWERTY keyboard with 10 user definable function keys. The<br />
keyboard has two key rollover and auto repeat.<br />
■ Internal 240/115V power supply is fully encased and made to BS Class 1.<br />
■ The internal loudspeaker is driven from a 3-voice music synthesis circuit with<br />
full ADSR envelope control.<br />
■ A fully modulated PAL colour television signal, for connection to a normal<br />
domestic television aerial socket, is available through a phono connector.<br />
■ A BNC connector supplies a composite video output to drive a black and white<br />
or PAL colour monitor.<br />
■ A standard audio cassette recorder can be used to record computer<br />
programs at 300 or 1200 baud using the CUTS standard tones. The cassette<br />
recorder is under full automatic motor control and is connected to the computer<br />
via a 7 pin DIN connector.<br />
■ An interrupt driven elapsed time clock enables real time control and timing<br />
of user responses.<br />
■ The unit uses a 2 MHz 6502 and includes 16K of Random Access Memory.<br />
■ A 16K Read Only Memory (ROM) integrated circuit contains an extensive and<br />
powerful Machine Operating <strong>System</strong> designed to interface easily to high level<br />
languages.<br />
■ A further 16K "Language ROM" contains an extremely powerful and fast<br />
BASIC interpreter. The interpreter includes a 6502 assembler which enables<br />
BASIC statements to be freely mixed with 6502 assembly language.<br />
■ Up to four 16K Language ROMs may be plugged into the machine at any time.<br />
These four ROMs are "paged" and may include Pascal, Word Processing,<br />
computer aided design software, Disk and Econet routines or Teletext<br />
acquisition software.<br />
■ The standard television output is 625 line 50 Hz, interlaced, fully encoded P"'<br />
modulated on UHF channel 36. Other standards are available.<br />
■ The full-colour Teletext display of 40 characters by 25 lines has full character<br />
rounding with double height, flashing, coloured background and text— all to the<br />
Teletext standard.<br />
■ The non Teletext display modes provide user definable characters in<br />
addition to the standard upper and lower case alpha-numeric font. In these<br />
modes, graphics may be freely mixed with text. Text characters can be<br />
positioned not only on, for example, a 40x32 grid, but at any intermediate<br />
position.<br />
■ Separate or overlapping text and graphic windows can be easily user-defined<br />
over any area of the display. Each of these windows may be filled and scrolled<br />
separately.<br />
■ The Model A is able to support the following modes:<br />
4 320x256 2 colour graphics and 40x32 text<br />
5 160x256 4 colour graphics and 20x32 text<br />
6 40x 25 2 colour text<br />
7 40x 25 Teletext display
■ All graphics access is "transiparent" resulting in a fast snow-free display.<br />
■ Extensive support is provided in the Machine Operating <strong>System</strong> for the<br />
graphics facilities, and this is fully reflected in the BASIC interpreter. These<br />
facilities include the ability to rapidly draw lines and to fill large areas of colour.<br />
In addition, very rapid changes of areas of colour can be effected.<br />
■ The Model A <strong>BBC</strong> <strong>Microcomputer</strong> <strong>System</strong> can be expanded at any time to the<br />
Model B <strong>System</strong>. In addition, or as an alternative, other facilities such as the<br />
Econet, may be fitted within the computer systems.<br />
Model B <strong>BBC</strong> <strong>Microcomputer</strong> <strong>System</strong><br />
The Model B <strong>BBC</strong> <strong>Microcomputer</strong> <strong>System</strong> is an enhanced version of the Model A<br />
<strong>Microcomputer</strong> but with the following differences:<br />
■ 32K Random Access Memory (RAM). This enables all the graphics modes to be<br />
used<br />
0 640x256 2 colour graphics and 80x32 text (20K)<br />
1 320x 256 4 colour graphics and 40x32 text (20K)<br />
2 160x 256 16 colour graphics and 20x32 text (20K)<br />
3 80x 25 2 colour text (16K)<br />
4 320x256 2 colour graphics and 40x32 text (10K)<br />
5 160x256 4 colour graphics and 20x32 text (10K)<br />
6 40x 25 2 colour text (8K)<br />
7 40x 25 Teletext display (1 K)<br />
■ The installed RAM is divided between the high resolution graphics display, the<br />
user's program and Machine Operating <strong>System</strong> variables. The 'Machine<br />
Operating <strong>System</strong> requires about 3 1/4K of RAM in the Model A. If higher<br />
resolutions are required with large programmes then the second processor<br />
option may be fitted.<br />
■ Serial interface to RS423 standard. The new standard has been designed to be<br />
inter-operable with RS232C equipment but offers a considerably enhanced<br />
specification — for example in maximum length of cable and maximum data<br />
transfer rates. Baud rates are software selectable between 75 baud and 9600<br />
baud. The interface provides not only two-way data transfer, but also two way<br />
hand-shaking using RTS and CTS lines. Connection to the machine is made via a<br />
5 way "diamond" DIN connector and various interconnecting plugs are<br />
available for the various standard 25 way D type circuits.<br />
■ An 8 bit "Centronics type" parallel printer port is provided with "Strobe" and<br />
"Acknowledge" lines.<br />
■ An 8 bit input/output port is also provided.<br />
■ 4 12 bit analogue input channels are provided. Each channel has an input<br />
voltage range of 0-2.5V and the internal converter provides a number in the<br />
range 0 to 4095. The conversion time for each channel is 10 milliseconds and<br />
when the conversion is complete, the processor is interrupted and the value<br />
stored in a memory location for later access. These analogue inputs can be<br />
used not only in laboratory control situations, but also as inputs for<br />
games—paddles or joysticks.<br />
■ A 1 MHz buffered extension bus is provided for connection to PRESTEL,<br />
Teletext or various other expansion units.<br />
■ All interface sockets to external peripherals, are fitted to the Model B. These<br />
include R/G/B/Sync for colour monitors, Econet, serial interface, parallel printer,<br />
disk and tube. Having the interface sockets fitted enables the internal<br />
expansions mentioned above to be fitted without further soldering.<br />
5
Both Model A and Model B may have the following expansion options fitted<br />
internally at purchase, or by Dealers at a later date.<br />
■ Floppy disk interface<br />
■ Econet network interface (separate leaflet available)<br />
■ Voice synthesis circuits<br />
■ Cartridge ROM pack interface<br />
■ Various alternative high-level languages in ROM<br />
External options which plug directly into the machine include:<br />
■ Paddles<br />
■ Cassette Recorder<br />
■ Black and White and colour monitors and televisions<br />
■ 5 1/4" single-sided disk drive (100K)<br />
■ 51/4" dual double-sided double track density disk drives (800K)<br />
■ 80 column dot-matrix printer<br />
■ Daisy Wheel Printer<br />
■ Teletext acquisition unit t both of these enable Telesoftware to be<br />
■ Prestel acquisition unit f downloaded into the <strong>BBC</strong> Computer as well as<br />
providing access to the normal<br />
Teletext/Prestel services. Pages may be<br />
"grabbed" and stored for later use<br />
■ 3MHz 6502 second processor with 60K of RAM<br />
■ Z80 second processor with 60K of RAM and a fully CP/M-compatible operating<br />
system<br />
Considerable attention has been paid to the overall design of the system and<br />
application software. A modular approach has been adopted specifically to ease<br />
the interfacing of various high-level languages (such as BASIC and Pascal) to the<br />
operating system.<br />
■ Machine Operating <strong>System</strong> (MOS)<br />
A 16K ROM is used for the MOS. This software controls all input/output device ,<br />
using a well defined interface. The MOS supports the following interrupts:<br />
❑ Event Timer (used as elapsed time clock)<br />
❑ 4 channel analogue to digital converter<br />
❑ Vertical sync<br />
❑ Keyboard and keyboard buffer<br />
❑ Tube byte transfer<br />
❑ Music tone generation and buffer<br />
❑ Serial interface, input and output, and buffers<br />
❑ Parallel input/output port<br />
and "hooks" are provided to support other devices such as:<br />
❑ Teletext<br />
❑ Prestel<br />
❑ Econet file system<br />
❑ Disk file system<br />
Many of the operating system calls are vectored to enable the user to change<br />
them if required at a future date.
■ BASIC<br />
The BASIC interpreter is an extremely fast implementation, very close to the<br />
Microsoft standard but with numerous powerful extensions:<br />
❑ Long variable names<br />
❑ Integer, floating point and string variables<br />
❑ Multi-dimension integer, floating point and string arrays<br />
❑ Extensive supportfor string handling<br />
❑ IF ... THEN ... ELSE<br />
❑ REPEAT... UNTIL<br />
❑ Multi-line integer, floating point and string functions<br />
❑ Procedures<br />
❑ Local variables<br />
❑ Full recursion on all functions and procedures<br />
❑ Effective error trapping and handling<br />
❑ Cassette loading and saving of programs and data<br />
❑ Full support for the extensive colour graphics facilities<br />
❑ Easy control of the built-in music generation circuits<br />
❑ Built-in 6502 mnemonic assembler enabling BASIC and assembler to be mixed,<br />
or pure assembly language programs to be produced.<br />
■ Other High Level Software<br />
A range of other high level software is presently under development or being<br />
commissioned. It is envisaged that a number of the larger programs will be<br />
available on ROMs which can be left in the machine and used as needed. It is<br />
hoped that these will include Pascal, Computer Aided Design package, and Word<br />
Processing. Details will be announced.<br />
■ Applications Software<br />
A range of applications packages is being developed<br />
atthe same time as the computer equipment. Each computer will be<br />
accompanied by a substantial, free 'welcome' cassette which<br />
will illustrate the wide range of things the computer is<br />
capable of doing. Other packages within the initial inventory,<br />
to be ready late 1981, include:<br />
❑ A home finance package<br />
❑ A computer aided design 'starter' package<br />
❑ A music package<br />
❑ Games packages<br />
❑ A home data-base package<br />
❑ Various programsto develop skills in primary school Maths and English,<br />
and in pattern matching<br />
❑ Scientific and business simulations<br />
❑ Programs which 'learn'<br />
At a later date (early 1982 onwards) more substantial programs which are<br />
envisaged include word processing, enhanced graphics packages,<br />
engineering packages, a VAT. package, a high level language utility, energy saving<br />
calculations, a more advanced music package, an astronomy pack, etc. Details<br />
of the full <strong>BBC</strong> software library will be announced as they become available.
The Econet communications network enables a number of computers to share<br />
expensive resources such as a printer and a disk "file server". The system is<br />
primarily intended for schools and colleges but also lends itself to many office and<br />
business applications.<br />
■ Up to 254 stations may share the network facilities<br />
■ Connection between stations is by cheap 4 wire "telephone" cable<br />
■ The network may be up to 1 kilometre from end to end<br />
■ Very low interface cost on each computer<br />
■ More than one printer or file server may be on the net<br />
■ Any station can "VIEW" any other similar station's screen<br />
■ Messages may be passed between any machines<br />
■ All inter-machine interaction can be barred to any specific machine or group of<br />
machines<br />
Because of the low costs involved, it is possible to dedicate one computer as art re<br />
server and one as a printer server. However, once pupils have loaded files from<br />
the file server, there is no reason why the file server computer should not be used<br />
as a normal disk computer until it is again required to act as a file server. The same<br />
flexibility applies to the printer server.<br />
Technical support and service can be obtained from a number of sources:<br />
■ Pre-sale advice (please send a large S.A.E.) from<br />
<strong>BBC</strong> <strong>Microcomputer</strong> <strong>System</strong><br />
PO Box 7<br />
London W3 6XJ<br />
■ After sales service and advice by a National Dealer Network<br />
■ Warranty repairs by Currys Ltd<br />
This description and specification is subject to change without notice.<br />
September 1981 <strong>Information</strong> <strong>Sheet</strong> <strong>G2</strong>