Various implementations of Loxone Link and Loxone Tree Bus on a STM32F103VET6, which can be bought with a CAN bus, RS232 and RS485 for a bit more something between 10-25 Euro at e.g. Aliexpress. The prices seem to vary a lot, it is worth to shop around for any STM32F103 with a CAN bus.

Project for the CrossWorks for ARM 4.4 from Rowley Associates.

Examples for:

• DMX Extension
• Modbus Extension
• Relay Extension
• RS232 Extension
• DI Extension
• Tree Extension with support for multiple tree devices:
  • Tree Alarm Siren
  • Tree RGBW Dimmer
  • Tree Room Comfort
  • Tree Touch

Multiple extensions and even tree devices behind multiple Tree extensions are possible.

Please read the protocol documentation at https://github.com/sarnau/Inside-The-Loxone-Miniserver for more details.