nRF21540 DK

Overview

The nRF21540 DK (PCA10112) shows possibility of the Nordic Semiconductor nRF21540 Front End Module connected with nRF52840 ARM Cortex-M4F CPU.

More information about the board can be found at the nRF21540 website [2]. nRF21540 Product Specification [4] contains the processor’s and front end module’s information and the datasheet.

Hardware

The nRF52840 on the nRF21540 DK has two external oscillators. The frequency of the slow clock is 32.768 kHz. The frequency of the main clock is 32 MHz.

Supported Features

The nrf21540dk board supports the hardware features listed below.

on-chip / on-board
Feature integrated in the SoC / present on the board.
2 / 2
Number of instances that are enabled / disabled.
Click on the label to see the first instance of this feature in the board/SoC DTS files.
vnd,foo
Compatible string for the Devicetree binding matching the feature.
Click on the link to view the binding documentation.

See nRF52840 Product Specification [3] and nRF21540 DK Hardware guide [1] for a complete list of nRF21540 Development Kit board hardware features.

Connections and IOs

LED

  • LED1 (green) = P0.13

  • LED2 (green) = P0.14

  • LED3 (green) = P0.15

  • LED4 (green) = P0.16

Push buttons

  • BUTTON1 = SW1 = P0.11

  • BUTTON2 = SW2 = P0.12

  • BUTTON3 = SW3 = P0.24

  • BUTTON4 = SW4 = P0.25

  • BOOT = SW5 = boot/reset

Front End Module

  • MOSI = P1.13

  • MISO = P1.14

  • CLOCK = P1.15

  • CHIP SELECT = P0.21

  • PDN = P0.23

  • MODE = P0.17

  • RXEN = P0.19

  • ANTSEL = P0.20

  • TXEN = P0.22

Programming and Debugging

The nrf21540dk board supports the runners and associated west commands listed below.

flash debug

Applications for the nrf21540dk/nrf52840 board configuration can be built, flashed, and debugged in the usual way. See Building an Application and Run an Application for more details on building and running.

Flashing

Follow the instructions in the Nordic nRF5x Segger J-Link page to install and configure all the necessary software. Further information can be found in Flashing. Then build and flash applications as usual (see Building an Application and Run an Application for more details).

Here is an example for the Hello World application.

First, run your favorite terminal program to listen for output.

$ minicom -D <tty_device> -b 115200

Replace <tty_device> with the port where the board nRF21540 DK can be found. For example, under Linux, /dev/ttyACM0.

Then build and flash the application in the usual way.

# From the root of the zephyr repository
west build -b nrf21540dk/nrf52840 samples/hello_world
west flash

Debugging

Refer to the Nordic nRF5x Segger J-Link page to learn about debugging Nordic boards with a Segger IC.

Testing the LEDs and buttons in the nRF21540 DK

There are 2 samples that allow you to test that the buttons (switches) and LEDs on the board are working properly with Zephyr:

samples/basic/blinky
samples/basic/button

You can build and flash the examples to make sure Zephyr is running correctly on your board. The button and LED definitions can be found in boards/nordic/nrf21540dk/nrf21540dk_nrf52840.dts.

Changing UART1 pins

The following approach can be used when an application needs to use another set of pins for UART1:

  1. Add devicetree overlay file to the main directory of your application:

    &pinctrl {
   uart1_default_alt: uart1_default_alt {
      group1 {
         psels = <NRF_PSEL(UART_TX, 0, 14)>,
                 <NRF_PSEL(UART_RX, 0, 16)>;
      };
   };
   /* required if CONFIG_PM_DEVICE=y */
   uart1_sleep_alt: uart1_sleep_alt {
      group1 {
         psels = <NRF_PSEL(UART_TX, 0, 14)>,
                 <NRF_PSEL(UART_RX, 0, 16)>;
         low-power-enable;
      };
   };
};

&uart1 {
  pinctrl-0 = <&uart1_default_alt>;
  /* if sleep state is not used, use /delete-property/ pinctrl-1; and
   * skip the "sleep" entry.
   */
  pinctrl-1 = <&uart1_sleep_alt>;
  pinctrl-names = "default", "sleep";
};

    In the overlay file above, pin P0.16 is used for RX and P0.14 is used for TX

See Set devicetree overlays for further details.

Selecting the pins

Pins can be configured in the board pinctrl file. To see the available mappings, open the nRF52840 Product Specification [3], chapter 7 ‘Hardware and Layout’. In the table 7.1.1 ‘aQFN73 ball assignments’ select the pins marked ‘General purpose I/O’. Note that pins marked as ‘low frequency I/O only’ can only be used in under-10KHz applications. They are not suitable for 115200 speed of UART.

References