Board-Mounted Wireless M-Bus




The RF-Module integrates a low power RF transceiver, a Cortex-M3 microcontroller and a matched ceramic antenna on a small PCB. The microcontroller provides configurable interfaces and abstracts the details of the RF implementation. Out of the box, a UART and a USB-interface are provided by the microcontroller firmware.

  • Cortex-M3 microcontroller
  • Low-power sleep mode
  • Full-Speed USB interface

The microcontroller runs Chipmunk, Theobroma’s multi-tasking embedded OS based on industry-standard FreeRTOS. It enables easy customization for user-defined applications and interfaces.

Software Stack

The software stack running on the RF-Module’s STM32 microcontroller allows to configure run-time parameters via its control interface as well as to send and receive RF messages. An implementation of the wireless M-Bus protocol is provided, including the RF communication modes R, S and T. Those modes provide different data-rate, frequency, and encodings for maximum flexibility.

The firmware of the RF-Module has been optimized for low- power consumption, making it ideal for battery-driven devices. It also provides a low-power mode in which the device spends most of its time in standby-mode and automatically wakes up after a configurable time.

  • Modular software architecture
  • Based on industry-proven real-time OS
  • Firmware upgradeable through USB

A stand-alone control application can be used to communicate with the RF-Module, i.e. using a USB host.

This firmware has been developed using software development best practices, i.e. high test-coverage, and is therefore highly reliable. Integration tests, as well as unit-tests, ensure the stability of the firmware.

Evaluation Kit available

The evaluation kit comprises one RF-Module and evaluation board. This evaluation board provides standard interfaces such as USB, UART, and SPI connectors. It also integrates a JTAG-debugger which eliminates the need of external debugging hardware and supports the GDB protocol.

Several tests are available to demonstrate the communication between two evaluation kits, including in the RF modes R, S, and T.

Gnat Development Kit

The Gnat development kit includes everything you need to get started integrating the RF module into your product.

The board exposes Gnat’s most used digital interfaces to standard connectors.

RS232: DB-9 Connector (TTL level available on pin header)

USB: Micro-USB jack “DUT”

All other interfaces are routed to 2.54mm headers.

The development kit includes an on-board JTAG debugger for a frictionless development experience. The embedded GDB server shows up as a standard USB-serial bridge. (Micro-USB jack “PROBE”). The whole board can be operated USB-powered or can be supplied from a 5mm DC barrel plug.


Common Footprint and Pinout

  • 37.5 x 15.0 mm
  • 3.3V single supply
  • Antenna area: On-board chip antenna or SMA connector

  • Digital Interfaces
  • USB FS

  • RF features
  • Integrated high-efficiency ceramic antenna
    Programmable output power up to +12dBm
    Over 600 meters range in open space – line of sight
    Wireless M-Bus compliant
    128 bit AES encryption
    Data rate up to 66kbit/s (mode T)
    Listen before talk function

  • Power Supply
  • 3.3V single supply

  • Consumption
  • Transmitting at maximum power: 160mW Receiving: 123mW Standby: 11μW
  • Operating environment
  • -20C to 70C

  • Dimensions
  • 15x37.5mm


Module Documentation

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