The Launchkey has two MIDI interfaces, providing two pairs of MIDI inputs and outputs over USB. They are as follows:
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MIDI In/Out (or first interface on Windows): This interface is used to receive MIDI from performing (keys, wheels, pad, pot, and fader Custom Modes); and is used to provide external MIDI input.
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DAW In/Out (or second interface on Windows): This interface is used by DAWs and similar software to interact with the Launchkey.
The Launchkey also has a MIDI DIN output port, which transmits the same data a as is received on host port MIDI In (USB). Note that this excludes responses to requests issued by the host to the Launchkey on MIDI Out (USB).
If you wish to use Launchkey as a control surface for a DAW (Digital Audio Workstation), you will likely want to use the DAW interface (See DAW Mode).
Otherwise, you may interact with the device using the MIDI interface.
The Launchkey sends Note On (90h (144) – 9Fh (159)) with velocity zero for Note Offs. It accepts either Note Offs (80h (128) – 8Fh (143)) or Note Ons (90h (144) – 9Fh (159)) with velocity zero for Note Off.
All SysEx messages begin with the following header, regardless of direction (Host → Launchkey or Launchkey → Host):
Regular SKUs:
Hex: F0h 00h 20h 29h 02h 14h
Dec: 240 0 32 41 2 20
Mini SKUs:
Hex: F0h 00h 20h 29h 02h 13h
Dec: 240 0 32 41 2 19
After the header is a command byte, selecting the function to use, and then whatever data is required for that function.