UART not sending data to FTDI USB

[Doug_H]

I can't get my PCA10040 board to send serial data when connected to a FTDI USB dongle. When the FTDI dongle is disconnected, and I connect my logic analyzer to the tx and gnd pins assigned on to the UART on the PCA10040 board it works perfectly. But as soon as I connect the FTDI dongle to the same pins, I get no serial data detected on the dongle and no serial data detected on the logic analyzer.

Any ideas what could be causing this?

This is the same dongle I use all the time on my STM32 boards and it works fine, so I know it's OK.

Here is a link to a photo of the setup: www.dropbox.com/.../IMG_5031.JPG

[endnode]

Have you tried SEGGER J-Link OB COM port on the DK itself? If that works then I'm sorry but it's somewhere in your wiring or FTDI dongle (the fact that it works with STM32 board is encouraging but not a proof of anything).

One more thing: P0.26 and P0.27 are used in I/O expander connection (see Table 5 in nRF52 DK User Guide). I don't see any reason why this should cause the effect but I cannot exclude it so going with some different PIN (not connected to any HW feature on DK;) might be also good debugging step. Actually many PINs are usable if you short Arduino shield detect PIN on P5 header...