EFR32 BRD4250B (SLWRB4250B)


The EFR32FG1 Flex Gecko 2.4 GHz and 868 MHz Radio Board is delivered as part of SLWSTK6061B Proprietary Wireless Starter Kit. It contains a EFR32FG1 Wireless SoC built on an ARM Cortex®-M4F processor with excellent low power capabilities.

SLWRB4250B Flex Gecko 2.4 GHz and 868 MHz Radio Board

SLWRB4250B (image courtesy of Silicon Labs)

The BRD4250B a.k.a. SLWRB4250B radio board plugs into the Wireless Starter Kit Mainboard BRD4001A and is supported as one of EFR32 Radio Boards.


  • EFR32FG1P133F256GM48 Flex Gecko SoC

  • CPU core: ARM Cortex®-M4 with FPU

  • Flash memory: 256 kB

  • RAM: 32 kB

  • Transmit power: up to +13 dBm

  • Operation frequency: 2.4 GHz, 868 MHz

  • 8Mbit SPI NOR Flash

  • Crystals for LFXO (32.768 kHz) and HFXO (38.4 MHz).

For more information about the EFR32FG1 SoC and BRD4250B board, refer to these documents:

Supported Features

Please refer to EFR32 Radio Board Supported Features for details of the configuration and common features supported by the efr32_radio_brd4250b board.

The default configuration can be found in the defconfig file:


System Clock

The EFR32FG1P SoC is configured to use the 38.4 MHz external oscillator on the board.

Serial Port

The EFR32FG1P SoC has two USARTs and one Low Energy UARTs (LEUART). USART0 is connected to the board controller and is used for the console.

Programming and Debugging

Please refer to Programming and Debugging EFR32 Radio Board for details on the supported debug interfaces.


Connect the BRD4001A board with a mounted BRD4250B radio module to your host computer using the USB port.

Here is an example for the Hello World application.

# From the root of the zephyr repository
west build -b efr32_radio_brd4250b samples/hello_world
west flash

Open a serial terminal (minicom, putty, etc.) with the following settings:

  • Speed: 115200

  • Data: 8 bits

  • Parity: None

  • Stop bits: 1

Reset the board and you should see the following message in the terminal:

Hello World! efr32_radio_brd4250b