INMC 80 News


May–September 1981, Issue 4

Page 54 of 71

Sound & Music

Programmable Sound Generator

a review by Kevin Smith

Source: Easicomp Ltd., __ ______ _____, Sprowston, Norwich, ___ ___. COST 43.00 + VAT.

This unit uses the now ubiquitous AY-3-8910 chip, which can make all manner of weird noises, and comes complete with software on tape to do just that! Also provided are programs to examine and modify the internal registers of the AY-3-8910, and to test that it is fully functional. For those unfamiliar with this chip, it contains 3 square wave tone generators, a noise generator, mixers and amplitude controls, an envelope generator, and two TTL- compatible I/O ports, all of which are controlled via sixteen 8-bit registers. These are accessed via ports 2 and 3.

The unit is supplied built on a 8″ x 3″ double-sided fibreglass pcb, which plugs into the Nasbus. Unfortunately, no edge connector socket is supplied, and there are no daisy chain connections between lines 16 and 17, 19 and 20.

An onboard amplifier, based on a LM386, powers a 1/4W. speaker, which is more than adequate, but a 5-pin DIN socket is also provided for output to your hi-fi music centre.

Several pages of documentation are supplied, consisting mainly of photocopies of the I.C. manufacturer’s information, which is pretty comprehensive, although most of the examples given are for a 1-79MHz clock. This encouraged some fruitful experimentation. No circuit diagram is supplied.

In conclusion, I found the unit easy to use, although perhaps over-priced. Certainly, the addition of sound adds another dimension to your programs.

Music Board

a review by Ian Henderson

Source: BBF Engineering, __ ___ ____, Melbourn, Royston, Herts.

Price: 21.65 built and tested including VAT.

The Music Board is a small board (5″ x 3″) built on a single sided fibreglass PCB. Connection to the Nascom PIO is made via a 14 pin socket in the centre of the board. Output is via a 5 pin DIN socket that can be fed to an audio amp, or through, for example, a radio/​cassette or your hi-fi.

The Music Board is basically a tone generator giving 8 octaves of 12 notes. A variable resistor must be set to tune the master oscillator against a reference such as a tuning fork – alternatively a scope may be used. Once set the board is simplicity itself to operate. Seven bits of the PIO are used, giving 128 possible output codes, 00 to 7F. The first nibble selects one of the eight octaves, the second, one of the twelve notes. The remaining four codes in each sixteen bytes are ‘silent’. As the PIO latches the data written to it, any note set will continue until the PIO contents are changed.

As only one PIO port is used, two cards could be connected to the Nascom. In this case one of the oscillators is used to drive both cards. The effect of two cards together should be ‘interesting’.

Documentation is thorough, with good descriptions and examples. To sum it up, effective and economical.

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