nRF52840 DK project wrongly uses nRF52 DK pinout layout

[albertmarc8]

Hello,

It's my first issue here and I hope It's the correct place to fix this kind of issue. I have a nRF52840-DK which I have been trying to get a working basic example, turning on LEDs and getting the input from the buttons. However pins didn't seem to match on what is being initialized.

I've found the fix using #200 and taking the changes from sandeepmistry/arduino-nRF5#532.

In a few words, the pins from the nRF52 DK are being used instead of the nRF52840DK when this board is selected in a project.
Similar issues are #163 and #63.

Below is a working example and a longer explanation of what is happening.

First, we have to observe what is already defined in variant.h (easily accesible within Arduino.h file):

// LEDs
#define PIN_LED1                (6)
#define PIN_LED2                (7)
#define PIN_LED3                (8)
#define PIN_LED4                (9)
#define LED_BUILTIN             PIN_LED1

// Buttons
#define PIN_BUTTON1             (2)
#define PIN_BUTTON2             (3)
#define PIN_BUTTON3             (4)
#define PIN_BUTTON4             (5)

Then we can check on variant.cpp:

const uint32_t g_ADigitalPinMap[] = {
  // D0 - D7
  11, 
  12, 
  13, 
  14, 
  15, 
  16, 
  17, 
  18, 

  // D8 - D13
  19, 
  20, 
  ...
}; 

Now we look at nRF52840-DK's datasheet, Table 6: Button and LED connections mentions that for LEDs 1 to 4 we should be looking at P0.13 to P0.16, which do not match to any of the defined pins in Figure 21: Arduino signals routing on the nRF52840 DK for the nRF52840-DK (left side). On the other hand, if we look at nRF52 DK (right side), it does match the expected pins, which doesn't seem the correct behaviour as I have a nRF52840-DK. If we check nRF52 DK's datasheet, we get that LEDs 1 to 4 are mapped from P0.17 to P0.20.

In my case, to solve the issue what I had to do was remap the pins to match the nRF52 DK's support Arduino pinout (Figure 21) to match the pins from nRF52840 DK's Table 6, so a code example to blink the LEDs has to be like this:

#include <Arduino.h>

#define NRF52840DK_LED1 2 	// Pin matching to nRF52 DK's D2 (P0.13)
#define NRF52840DK_LED2 3 	// Pin matching to nRF52 DK's D3 (P0.14)
#define NRF52840DK_LED3 4 	// Pin matching to nRF52 DK's D4 (P0.15)
#define NRF52840DK_LED4 5 	// Pin matching to nRF52 DK's D5 (P0.16)

void setup()
{
	// put your setup code here, to run once:
	pinMode(NRF52840DK_LED1, OUTPUT);
	pinMode(NRF52840DK_LED2, OUTPUT);
	pinMode(NRF52840DK_LED3, OUTPUT);
	pinMode(NRF52840DK_LED4, OUTPUT);
}

void loop()
{
	digitalWrite(NRF52840DK_LED1, HIGH);
	digitalWrite(NRF52840DK_LED2, HIGH);
	digitalWrite(NRF52840DK_LED3, HIGH);
	digitalWrite(NRF52840DK_LED4, HIGH);
	delay(500);
	digitalWrite(NRF52840DK_LED1, LOW);
	digitalWrite(NRF52840DK_LED2, LOW);
	digitalWrite(NRF52840DK_LED3, LOW);
	digitalWrite(NRF52840DK_LED4, LOW);
	delay(500);
}

The platformio.ini is as simple as this:

[env:nrf52840_dk]
platform = nordicnrf52
board = nrf52840_dk
framework = arduino

Building and uploading the code below has correctly blinked the LEDs for me in a nRF52840-DK.

Same can be done with nRF52840 DK's onboard buttons. Important to configure the pinMode with INPUT_PULLUP for the buttons as specified by the datasheet, else it will fail.

#define NRF52840DK_BUTTON1 0 	// Pin matching to nRF52 DK's D0 (P0.11)
#define NRF52840DK_BUTTON2 1 	// Pin matching to nRF52 DK's D1 (P0.12)
#define NRF52840DK_BUTTON3 12 	// Pin matching to nRF52 DK's D12 (P0.23)
#define NRF52840DK_BUTTON4 13 	// Pin matching to nRF52 DK's D13 (P0.24)