Problem changing pins of gfx ST7735 Example in SDK 15.3

[Walther]

Hi all,

I am running in a strange problem. I am using the gfx example under peripheral with the nRF52840 DK and a display with ST7735 driver. I connected the display to the pins I found in the sdk_config.h:

ST7735_SCK_PIN 47 --> P1.15

ST7735_MOSI_PIN 45 --> P1.13

ST7735_SS_PIN 44 --> P1.12

ST7735_DC_PIN 42 --> P1.10

Everything worked fine with this configuration. Then I tried to change the configuration of all pins and the display did not work any more (showed just a white screen). From what I read about the GPIO pins I thought every configuration should be possible.

I then tried to change only one pin at a time and saw some strange behavior. I set the DC pin to different values:

ST7735_DC_PIN 40 --> P1.08 => worked

ST7735_DC_PIN 9 --> P0.09 => did not work (white screen)

ST7735_DC_PIN 32 --> P1.00 => worked

Then I set the DC Pin back to 42 and changed only the SCK pin:

ST7735_SCK_PIN 40 --> P1.08 => worked

ST7735_SCK_PIN 10 --> P0.10 => did not work (white screen)

So it seems like everything works fine as long as I take only pins of register 1, and problems occur as soon as I take pins of register 0. Do the pins have to be in the same register? Or am I connecting the cables to the wrong pins? Or is it something else what I am not thinking of?

Greetings

Walther

[Jørgen Holmefjord]

Hi,

Did you try other pins on port 0? P0.09 and P0.10 are used for the NFCT peripheral. If you want to use these pins as GPIOs on the DK, you need to make sure the preprocessor symbol CONFIG_NFCT_PINS_AS_GPIOS is set, and move 0R resistors from R44/R46 to R43/R45. Please have a look at the nRF52840 DK user guide.

Best regards,
Jørgen

[Walther]

Hi Jørgen,

I tried some others too, but it did also not work. Then, I found out P0.30 is working. Then I found this page in the documentation: https://infocenter.nordicsemi.com/topic/ug_nrf52840_dk/UG/nrf52840_DK/connector_if.html

It seems like I always took one of the already taken pins. Which are all in Register 0 obviously. I wanted to take these pins because I want to use my code on the dongle later on, but then I will stick to the pins now and change them when I switch to the dongle.

Thank you for the hint!