Test UART using GPIO

[Sridhar Jonnavittula]

Hi,

I want to test UART peripheral on nrf52840 by running example in path examples\peripheral\uart as it is.

Connection setup is:

nRF power source USB

nRF USB port connection

Default switch mode

Windows PC having USB to RS232 serial cable enumerating a COM port which its TX and RX pins connected to P0.06 GPIO TX pin, P0.08 RX GPIO pin on nrf52840 PDK

So while testing, most of the times some junk values are coming.

How to resolve this issue?

[cbd]

Hi,

Just to check:

1. Did you connect the ground wire from your USB-RS232 lead to a ground on the board?
2. Did you connect TX to RX on the lead to the board and vice versa?
3. Did you configure both ports for the same settings e.g. board rate, stop bits, parity, flow control etc?
4. Finally does the USB-RS232 lead give a 3.3V or a 5V output, you'll need 3.3V.

[Sridhar Jonnavittula]

1. I did not connect USB-RS232 ground pin 5 to any of GND pin on nrf52840 DK

2. Yes

3. 

and example application don't have Data and Stop bits. Where to set those values?

4. Yes

Is it OK to connect micro USB cable to USB J3 on nrf52840 DK for this test case?

[Marjeris Romero]

The UART signals are routed through the interface MCU,  can you try connecting your micro USB cable to the J2 connector instead?

If you are still having issues, could you please upload a picture or drawing of your setup so we can try to reproduce it?

[Sridhar Jonnavittula]

When I connect to J2 it is working fine with same COM port settings. But there may be cases where using GPIO on DK and USB-RS232 converter both as a combination is a requirement right. How to support this requirement.

[Marjeris Romero]

So if I understand correctly,  you want to connect the GPIO pins used for UART on the nRF52840 directly to a USB-RS232  serial converter cable (i.e. Digi-Key part # 768-1065-ND)?

Try first to connect USB-RS232 ground to any GND pin on the nrf52840 DK. You may also need to disconnect the interface MCU by switching SW6 to nRF ONLY or set other GPIO pins as UART RX/TX in software.

[cbd]

Agreed.

If you're using the GPIO lines to the interface MCU for your lead connection then you'll have issues, especially if your still using the USB port on the other side for debug.

I believe that there's a note that this shouldn't be done for fear of damaging the interface MCU.