Lauch Pad

Programmer’s Reference

1 Introduction
This manual describes Launchpad’s MIDI communication format. This is all the proprietary information you need to be able to write patches and applications that are customised for Launchpad. It is assumed that you already have a basic knowledge of MIDI, and some appropriate software for writing interactive MIDI applications (for example, Max for Live,Max/MSP, or Pure Data). Numbers in this manual are given in both hexadecimal and decimal equivalents, as different software favours the use of different conventions. To avoid any ambiguity, hexadecimal numbers are always followed by a lower-case h.

2 Launchpad MIDI Overview
Launchpad comprises eighty buttons. These divide into three sections: a square grid of sixty-four buttons, eight round‘scene launch’ buttons arranged along the right-hand side, and a row of round buttons at the top that are generally employed by Automap or Live. Every button is back-lit by a bi-coloured LED. Each LED consists of a red and a green element. When these are both turned on, the light can be mixed to form amber. All communication with Launchpad is conducted using MIDI note-on, note-off, and controller changemessages. Launchpad transmits and receives on MIDI channel 1. There is one exception to this, which will be covered later, but it is not essential to learn it. Hence a Launchpad MIDI message is always three bytes long. (For good reasons, the driver does not support running status.) A valid message therefore takes one of these forms: Message type Note off Note on Controller change Hex version 80h,Key, Velocity 90h, Key, Velocity B0h, Controller, Data Decimal version 128, Key, Velocity 144, Key, Velocity 176, Controller, Data

Launchpad uses a low-speed version of USB. A limitation of this is that it accepts a maximum of 400 messages per second. Because there are 80 LED addresses (one for each bi-colour LED), it will take 200 milliseconds to update a Launchpad completely. Two work-aroundsare provided to speed up its real and apparent update speed: • MIDI channel 3 note-on messages (beginning 92h, or 146 decimal) can be used to update the entire surface two LEDs at a time. Launchpad can be double-buffered. This means that all the LED states can be updated internally while they continue to show their existing state. The buffers may then be swapped with a single command, so that theupdate of the surface appears to be instantaneous.

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Launchpad Programmer’s Reference

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3 Computer-to-Launchpad Messages
Note Off
Hex version Decimal version 80h, Key, Velocity 128, Key, Velocity

This message is interpreted in exactly the same way as a note-on message containing the same key code, and velocity zero. The velocity byte contained within the note-off message isignored.

Set grid LEDs
Hex version Decimal version 90h, Key, Velocity. 144, Key, Velocity.

A note-on message changes the state of a grid LED. Key is the MIDI note number, which determines the LED location. Velocity is used to set the LED colour. Launchpad can be configured to map its buttons to MIDI note messages in one of two ways. The differences between these mapping modes are covered later,and can be seen in Figures 1 and 2. The default mapping is the X-Y layout. In this mapping, locations are addressed as follows, with the origin being the square button at the top-left corner of the grid: Hex version Decimal version Key = (10h x Row) + Column Key = ( 16 x Row) + Column

The scene launch buttons (the round buttons with printed triangles) are column 8. Invalid column numbers (9 to15) are also interpreted as column 8.. Velocity is determined as follows (those unfamiliar with binary notation can read on for the formula): Bit 6 5..4 3 2 Name Green Clear Copy Meaning Must be 0. Green LED brightness. If 1: clear the other buffer’s copy of this LED. If 1: write this LED data to both buffers. Note: this behaviour overrides the Clear behaviour when both bits are set. Red LED...