3 Specification 3.1 The microcomputer The microcomputer is contained in a rigid injection moulded thermoplastic case, and provides the following facilities. 73 key full travel QWERTY keyboard including 10 user-definable function keys. Keyboard has two key rollover and auto repeat. Fully encased internal power supply manufactured to BS 415 Class 1. Internal loudspeaker driven from a 4-channel sound synthesis circuit with ADSR envelope control. A colour television signal, for connection to a normal domestic television aerial socket, is available through a phono connector. This signal is 625 line, 50Hz, interlaced, encoded PAL A and is modulated on UHF channel 36.
A BNC connector supplies a composite video output to drive a black and. white or PAL colour monitor. 6-pin DIN connector provides separate RGB and sync outputs at TTL levels. RGB are all high true, and sync is link selectable as high or low true, pulse duration 4.0 microseconds. A standard audio cassette recorder can be used to record computer programs and data at 300 or 1200 baud using the Computer Users' Tape Standard tones. The cassette recorder is under automatic motor control and is connected to the computer via a 7-pin DIN connector. An interrupt driven elapsed time clock (user settable). 6512A processor running at 2MHz.
64K of read/write Random Access Memory (RAM), allowing a shadow screen mode, and 12K paged RAM in any mode. 32K Read Only Memory (ROM) integrated circuit containing the Machine Operating System and a fast BASIC interpreter. The interpreter includes a 6502/6512 assembler which enables BASIC statements to be freely mixed with 6502/6512 assembly language. Code generated using the BASIC assembler can be run on a machine with a 6512 microprocessor, or a machine with a 6502 microprocessor. Up to five 32K sideways ROMs may be plugged into the machine at any time, having the effect of ten 16K ROM slots (eleven including BASIC).
These ten 16K ROM slots are paged and may include Pascal, word processing, computer aided design software, disc and ECONET and WINCHESTER filing systems or TELETEXT acquisition software. The full-colour Teletext display of 40 characters by 25 lines, known as mode 7, has character rounding, with double height, flashing, coloured background and text plus pixel graphics - all to the Teletext standard. The non-Teletext display nodes (modes 0 to 6) provide user-definable characters in addition to the standard upper and lower case alpha- numeric font. In these modes, graphics may be mixed freely with text. 3