RTT works but Serial doesnt

[bem22]

As the title says, I'm struggling to make the serial interface work with nRF5240 CKAA

I'm using nRF52840DK for flashing the chip by using the P20 header to power and connect to the target (3V0, SWD CLK, SWD IO) and GND from outside the header.

As said, RTT connects by itself when automatically searching for it, but Serial communication doesn't work and I am not sure if  my settings are to blame.

I am using the 52840DK config to which I added this prj.conf

# Logger module
CONFIG_LOG=y

# Button and LED library
CONFIG_DK_LIBRARY=y

CONFIG_I2C=y

# Bluetooth LE
CONFIG_BT=y
# STEP 1 - Include the Peripheral Role support

CONFIG_BT_PERIPHERAL=y

# STEP 2 - Change the Bluetooth LE device name to Nordic_Peripheral
CONFIG_BT_DEVICE_NAME="TEST_UNIT_4"

# Increase stack size for the main thread and System Workqueue
CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=2048
CONFIG_MAIN_STACK_SIZE=2048

CONFIG_CLOCK_CONTROL_NRF_K32SRC_XTAL=n
CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=y

CONFIG_BOARD_ENABLE_DCDC=n

What am I missing?

[Jørgen Holmefjord]

Hi,

Your configs does not seem to configure anything related to serial interfaces. I assume you are referring to the UART interface when you say serial interface?

Do you expect the serial output through the logger, or some part of your application (e.g. using the UART driver API)?

Have you connected the UART pins of the external board to something where you will read the output?

Lesson 5 in the nRF Connect SDK Fundamentals course in our Developer Academy is a good introduction to UART. Lesson 4 regarding console and logger output also seems relevant to your question.

Best regards,
Jørgen

[bem22]

I mean Serial Port (through COM). I need this just for logging

For some reason, Hello World won't display anything in the console although the console says it's connected

[Jørgen Holmefjord]

From the serial number of the connected device, it looks like you have opened the COM port to one of our DKs. This will always work when the DK is powered, as the virtual COM interface runs on the interface MCU on the DK (J-Link debugger chip). The UART interface to the interface MCU is hardwired to the nRF chip on the DK, but it will not go to any external board, that would require you to manually connect the UART pins from the external board to the UART pins on the DK.

Can you please describe your setup in more details?

[bem22]

Oh. This I didn't know.

We have a custom PCB with nRF52840, which connects to the DK via a JTAG cable

I wish to know if P1.00 has anything to do with UART.

Otherwise, I think there are not many options except for using RTT for now, as most of the other pins are not accessible anywhere else on this prototype.

[Jørgen Holmefjord]

Any GPIOs can be assigned to any serial interface on the nRF52840. By default, the UART TX pin is configured to GPIO P0.06, but this can be changed in the devicetree/overlay files when building a project in nRF Connect SDK.