JasperMIDI guide
The Link Bus
T A B C D E F
Trigger Note 1 lsb Note 2 Note 3 Note 4 msb Octave 1 lsb Octave 2 msb
The Link bus uses 5V TTL logic levels.
Notes are encoded as a number from 0-11 from top to bottom using bits A-D. The octave on bits E
and F from 0-2, 0=high, 1=mid, 2=low.
The trigger is a pulse approximately 50Hz when active, and the note data is decoded on its rising
edge.
When not actively playing a note, the lines on the Link bus should be put in a hi-Z state, in order
that other equipment can use the bus. On a microcontroller this usually means switching the pins
to Input mode with any internal pull-up resistors switched off.
The Wasp/Jasper keyboard allows playing of the top two octaves, but by using the Link port
another octave is possible, shown in grey above. There is a hardware ‘bug’ in the Wasp/Jasper
decoding circuitry – the lowest C (C0 above) is not decoded, so it won’t play. The Gnat decoding
circuitry can play the lowest C.
The note codes are shown in decimal in the above graphic. Between the C#s and Cs there is a gap
of four – this is because the note numbers only count from 0-11 per octave. Numbers 12-15 are
skipped/ignored by the decoding logic in the synths.
Mapping Link to MIDI
The following table shows the MIDI note numbers used by JasperMIDI, and the corresponding
number of each note on the Link bus:
Note Octave C0 C0# D0 D0# E0 F0 F0# G0 G0# A1 A1# B1
MIDI Note 36 37 38 39 40 41 42 43 44 45 46 47
Link Note 48 43 42 41 40 39 38 37 36 35 34 33
Note Octave C1 C1# D1 D1# E1 F1 F1# G1 G1# A2 A2# B2
MIDI Note 48 49 50 51 52 53 54 55 56 57 58 59
Link Note 32 27 26 25 24 23 22 21 20 19 18 17
Note Octave C2 C2# D2 D2# E2 F2 F2# G2 G2# A3 A3# B3 C3
MIDI Note 60 61 62 63 64 65 66 67 68 69 70 71 72
Link Note 16 11 10 9 8 7 6 5 4 3 2 1 0
Note: C0 doesn’t play on Jasper/Wasp – but is OK on the Gnat.
v1 Page 9 of 9 November 2017
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