The Fairlight Computer Musical Instrument is a complete music production and performance instrument. It is a special purpose computer system incorporating a custom dual M6809 central processor interfaced to special input-output devices optimised for the rather unusual requirements of music production. The C.M.I. is a complex special-purpose computer system which embraces many different hardware and software technologies. All processing and sound generation functions are performed by the Mainframe, while the Graphics Terminal and Keyboards serve as peripherals for operator interfacing. The mainframe is capable of operating quite autonomously, that is, it is not reliant on any external connections for proper functioning. Under certain conditions it is possible for a fault condition to inhibit proper Mainframe operation, so the serviceperson should be wary of being mislead. Of course, without the peripherals connected it is often hard to know if the system is functioning properly, but this point should be borne in mind when troubleshooting. Operator input to the Mainframe comes from three sources: music keyboard, alphanumeric keyboard and lightpen. Output devices include the Graphics Display terminal and the audio outputs. A printer may also be optionally used. The heart of the system is the Central Processing Module, which U3es two Motorola 6809 microprocessors in a dual-processor configuration. Both processors share a common buss which allows them both to communicate with the other cards in the Mainframe. The Processor Control Module provides EPROM for system startup and bootstrap, RS-232C serial input from the keyboard, serial output to the keyboard and printer, and various other C.P.U. support functions such as interrupt prioritisation. Main program memory is the 256K RAM card. This holds all the operational software, much of which is overlayed from disk as the code exceeds 25ÖK. The Floppy-disk controller uses Direct Memory Access techniques to transfer data between memory and the two floppy-disk drives. The Graphics Display is a bit-mapped image of 16K bytes of VRAM. This is displayed as an array of 256 by 512 points. Special hardware provides support functions for automatic vector drawing, which considerably enhances the speed of displaying graphical Information. Hit and touch signals from the Lightpen are interfaced to the system buss. Eight identical Voice Modules also share the buss. They each have 16K bytes of waveform RAM, as well as all the control and audio circuits required to support it. A Voice Master module controls the voice modules, as well as providing the Analog-to-Digital converter function of the system. Audio from the Voice Modules is buffered by the Audio Output Module, which provides independent balanced outputs for each channel as well as a mixed (LINE) output.