96Boards Neonkey


96Boards Neonkey board is based on the STMicroelectronics STM32F411CE Cortex M4 CPU. Zephyr applications use the 96b_neonkey configuration to run on these boards.

96Boards Neonkey

96Boards Neonkey

This board acts as a sensor hub platform for all 96Boards compliant family products. It can also be used as a standalone board.


96Boards Neonkey provides the following hardware components:

  • STM32F411CE in UFQFPN48 package
  • ARM® 32-bit Cortex®-M4 CPU with FPU
  • 84 MHz max CPU frequency
  • 1.8V work voltage
  • 512 KB Flash
  • 128 KB SRAM
  • On board sensors:
    • Temperature/Humidity: SI7034-A10
    • Pressure: BMP280
    • ALS/Proximity: RPR-0521RS
    • Geomagnetic: BMM150
    • Acclerometer/Gyroscope: BMI160
    • AMR Hall sensor: MRMS501A
    • Microphone: SPK0415HM4H-B
  • 4 User LEDs
  • 15 General purpose LEDs
  • GPIO with external interrupt capability
  • I2C (3)
  • SPI (1)
  • I2S (1)

Supported Features

The Zephyr 96b_neonkey board configuration supports the following hardware features:

Interface Controller Driver/Component
NVIC on-chip nested vector interrupt controller
SYSTICK on-chip system clock
UART on-chip serial port
GPIO on-chip gpio
PINMUX on-chip pinmux
FLASH on-chip flash
SPI on-chip spi
I2C on-chip i2c

More details about the board can be found at 96Boards website.

The default board configuration can be found in the defconfig file:


Connections and IOs


  • LED1 / User1 LED = PB12
  • LED2 / User2 LED = PB13
  • LED3 / User3 LED = PB14
  • LED4 / User4 LED = PB15

Push buttons

  • BUTTON = RST (SW1)
  • BUTTON = USR (SW2)

System Clock

96Boards Neonkey can be driven by an internal oscillator as well as the main PLL clock. By default System clock is sourced by PLL clock at 84MHz, driven by internal oscillator.

Serial Port

On 96Boards Neonkey Zephyr console output is assigned to USART1. Default settings are 115200 8N1.


96Boards Neonkey board has up to 3 I2Cs. The default I2C mapping for Zephyr is:

  • I2C1_SCL : PB6
  • I2C1_SDA : PB7
  • I2C2_SCL : PB10
  • I2C2_SDA : PB3
  • I2C3_SCL : PA8
  • I2C3_SCL : PB4


96Boards Neonkey board has one SPI. The default SPI mapping for Zephyr is:

  • SPI1_NSS : PA4
  • SPI1_SCK : PA5
  • SPI1_MISO : PA6
  • SPI1_MOSI : PA7

Programming and Debugging


Here is an example for building the Hello World application.

# On Linux/macOS
cd $ZEPHYR_BASE/samples/hello_world
mkdir build && cd build

# On Windows
cd %ZEPHYR_BASE%\samples\hello_world
mkdir build & cd build

# Use cmake to configure a Ninja-based build system:
cmake -GNinja -DBOARD=96b_neonkey ..

# Now run ninja on the generated build system:


96Boards Neonkey can be flashed by two methods, one using the ROM bootloader and another using the SWD debug port (which requires additional hardware).

Using ROM bootloader:

ROM bootloader can be triggered by the following pattern:

  1. Connect BOOT0 to VDD (link JTAG pins 1 and 5 on P4 header)
  2. Press and hold the USR button
  3. Press and release the RST button

More detailed information on activating the ROM bootloader can be found in Chapter 29 of Application note AN2606. The ROM bootloader supports flashing via UART, I2C and SPI protocols.

For flashing, stm32flash command line utility can be used. The following command will flash the zephyr.bin binary to the Neonkey board using UART and starts its execution:

$ stm32flash -w zephyr.bin -v -g 0x08000000 /dev/ttyS0


The above command assumes that Neonkey board is connected to serial port /dev/ttyS0.

Using SWD debugger:

For flashing via SWD debug port, 0.1” male header must be soldered at P4 header available at the bottom of the board, near RST button.

Use the Black Magic Debug Probe as an SWD programmer, which can be connected to the P4 header using its flying leads and its 20 Pin JTAG Adapter Board Kit. When plugged into your host PC, the Black Magic Debug Probe enumerates as a USB serial device as documented on its Getting started page.

It also uses the GDB binary provided with the Zephyr SDK, arm-zephyr-eabi-gdb. Other GDB binaries, such as the GDB from GCC ARM Embedded, can be used as well.

$ arm-zephyr-eabi-gdb -q zephyr.elf
(gdb) target extended-remote /dev/ttyACM0
Remote debugging using /dev/ttyACM0
(gdb) monitor swdp_scan
Target voltage: 1.8V
Available Targets:
No. Att Driver
 1      STM32F4xx
(gdb) attach 1
Attaching to Remote target
0x080005d0 in ?? ()
(gdb) load


After flashing 96Boards Neonkey, it can be debugged using the same GDB instance. To reattach, just follow the same steps above, till “attach 1”. You can then debug as usual with GDB. In particular, type “run” at the GDB prompt to restart the program you’ve flashed.