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MIDI AND THE AVR
I N T R O TO U S I N G T H E AV R I N M I D I A P P L I C A T I O N S
PAUL MADDOX
MARCH 2002

TABLE OF CONTENTS
Introduction .............................................................................................................................................2 MIDI, what is it?......................................................................................................................................2 MIDI specs, a quick guide .....................................................................................................................3 MIDI; the hardware.................................................................................................................................4 MIDIgotcha's..........................................................................................................................................7 MIDI to CV conversion; a quick project ..............................................................................................10 Useful links ...........................................................................................................................................11

INTRO USINGTHE AVR IN MIDI APPLICATIONS, PAUL MADDOX - AVRFREAKS.NET 1

Introduction
This guide is intended to help you on the way to useing MIDI with the AVR range of processors, explaining the concepts and protocols used to some of the gotchas and common problems people face. Where possible I've tried to kept the guide as processor independant as possible.

Assumptions

You need a certain amount ofknowledge about serial communication, not much, but a few basic concepts. Also a little understanding of the hardware involved, AVR, opto-isolators, etc. Also a basic knowledge of what a MIDI system is, e.g. Sequencer, synthesiser modules, keyboards.

Who is this bean?
My name is Paul Maddox and I'm a keen electronic/synth/micro enthusiast. That is to say I do this for fun, not for a living,you can see my web site here  www.wavesynth.com as you can see from the site its a fairly major part of my life. I wrote this as a guide to get people into useing AVRs for MIDI, Something that very few people seem to use them for, perhaps they dont know how to? If not, this will hopefully explain it.

MIDI, what is it?
So, what's all about? A few years back, quite a few actually, people couldsee the need for a common standard for communication between synthesizers. Many manufacturers had their own standards (V/hz, V/Oct, DCB, PPG BUS, etc) none of which were easily convertable to communicate with each other. With the increase of sequencers and affordable computers it was decided to got for a digital system, offering better accuracy and precision than the tradional CV/Gate type ofinterface. The standard they decided on was called MIDI and it stands for 'Musical Instrument Digital interface'. A webpage published by the organisation that was formed to control the standard is available at Http://www.MIDI.org/ and is a very useful resource for anything relating to MIDI. There are two parts of the MIDI system to consider, the hardware interface and the protocol used. The main bulkof the issues and problems with useing MIDI are to related to the protocol, so this document focuses mostly on this, though the hardware is mentioned.

Protocol

The MIDI system is based on the concept of the user being a keyboard player, rather than say a wind instrument or guitar payer. In its simplest form MIDI is the means by which note information is sent, e.g. when a 'key' on the keyboardis pressed. The type of information that is sent is event information and not audio. That is to say MIDI is used to describe when a note is pressed, which note it is, how hard and for how long, but not the sound that is created by this action. MIDI is also used for a whole host of other events, but the action of pressing a note is the simplist to describe and emphasise the point at hand. The...