9160DK: need HWFC between 9160 and 52840?

[bluebeam]

Hi,

I'm using the NRF9160DK board. I'd like to connect the UART port from 9160 to the 52840. The 9160 is running SLM firmware. The 52840 is running my code.

My question is about the uart hardware flow control. I assume it's still needed? I remember when I use 52832 in the past it's necessary to have HWFC. Is that still true?

When I enable HWFC on both sides, it seems working ok. When I send 'AT' from 52840 I got 'OK' back from 9160. But when I look at the actual lines, I noticed that nRF52 RTS (nRF91 CTS) is always low. Is that normal? I do have a BLE connection while doing these tests. I expect to see it toggling sometime. I do see the other line (NRF52CTS-NRF91RTS) toggles based on when I send 'AT' from NRF52 to NRF91.

I attached the configuration files for both the 52840 and 9160.

9160.prj.conf52840.prj.conf3835.nrf9160dk_nrf52840.overlay4405.nrf9160dk_nrf9160ns.overlay

[Albrecht Markus Schellenberger]

bluebeam said:

Why you say it's on the NRF91 side? If it's RTS for NRF52, then should it be on the NRF52 side?

My apologies for the confusion. You are right, it is the nRF52 side that doesn’t act as expected.

bluebeam said:

Is it possible that there's never been a conflict so there's no need to raise the line?

This could be an explanation, yes. One way to check if the line is okay could be to configure the UART on the nRF52 side with UART_CFG_FLOW_CTRL_NONE and use uart_line_ctrl to toggle the RTS line manually.

Regards,

Markus