MIDI decoding using 6402

[Paul Maddox]

Elliot,

  Im no expert on midi nor the 6402, but I made a midi>cv interface using 
the atmel avr (90s8515). Things to remember..

  when you press a key 3 things are sent;-

1)  databyte 8 bits (4 channel, 4 note on/off) 1001nnnn = Note on,           
           1000nnnn=NOte off.
2)  Note byte , 0nnnnnnn, as you said, MSB is 0
3)  Velocity , 0nnnnnnn, again 0 to 127. so if you were using say channel 1 
you would see this;-

10010000  - Note on, Channel 1
01010110  - Note to be played
01111000  - Velocity of note

When you let go, one of two things could happen.
you could get this

10000000  - Note off, Channel 1
01010110  - Note to be turned off
01111000  - Velocity

*BUT* what you usually get is this..

10010000  - note *ON*, channel 1
01010110  - Note to be turned off
00000000  - Velocity set to ZERO


so when you see the MSB flash its the note on/off command.
Now, there is another complication, running status.. for example if you 
pressed several notes in quick sucsession this would happen;-

10010000  - Note ON
01010110  - Note to be played
01111111  - Velocity

01010110  - NOte to be turned off
00000000  - Velocity

01010001  - Note to be played
01101001  - velocty

01010001  - note to be turned off
00000000  - Velocity.

if you press a chord a similar thing happens

10010000  - Note on/channel1
01010110  - First note
01111111  - velocity of first note
01010001  - Second note
01001111  - Velocity of second note
01010101  - Third note
01111111  - Velocity of third note

you notice that the noteon/channel info is missing.... if you p]lay slowly 
it'll be there , if its quick or a chord, its missing.

Good fun eh?

If I can help anymore, just ask..

Paul Maddox





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