How the sensors talk to the hub

ABW sensors don't need any special software on the SPIKE hub, because they pretend to be an official LEGO® SPIKE™ colour sensor. This page explains how that works. It's for curious and advanced users; you don't need any of it to use the sensors.

The LEGO UART protocol

SPIKE Prime sensors talk to the hub over a serial (UART) link on the port's data pins. The protocol is often called LPF2 or LUMP:

1. Handshake. When a device is plugged in, it introduces itself at 2400 baud: its type ID (the colour sensor is 0x3D), how many modes it has, and the name, range, units and data format of each mode.
2. Speed change. The device and the hub then switch to 115200 baud.
3. Data. The hub picks a mode, and the device sends readings for that mode. The hub sends a regular "keep-alive" message; if the device stops hearing it, it resets and repeats the handshake.

How ABW uses it

The ABW firmware (in src/core/) gives the full colour sensor handshake, so the hub and the SPIKE app treat the board as a genuine colour sensor. The sensor's own data is placed in the colour sensor's RGB_I mode (mode 5), which normally carries the raw red, green, blue and intensity values. That's why:

• your data shows up on the red, green and blue channels;
• each channel carries a 16-bit whole number;
• any software that can read a colour sensor's raw RGB values can read ABW sensors.

Credits

The protocol code is based on the open-source MyOwnBricks project by Ysard, and uses protocol definitions from Pybricks. The protocol itself is documented by the Pybricks team in pybricks/technical-info. See Licences.