I'm trying to connect external nrf52832 module to nrf52-dk (PCA10040). I use wiring scheme from this picture:

And it works fine for programming. But I can't get RTT messages from my external module - only from onboard chip.
I suppose this may require some electonic or programm configuration to switch RTT source. But I can't find any information about it.
I use PlatformIO as IDE and ZephyrRTOS as Framework. Just for testing I use primitive code like this:
void main (void)
{
while (1) {
k_sleep (K_MSEC (500));
printk ("Hello \n");
}
}
May be I missed something or did wrong? How to get RTT from external module correctly?