Nrf9160 doesn't answer via UART

[Dmitry Krol]

Hello.

Our design is our host processor that communicates with nrf9160 via uart (AT commands). Everything works fine, but sometimes nrf9160 doesn't answer to AT command till we perform hard reset to nrf9160. Do you have idea what can cause this problem?

[Dmitry Krol]

*Stops to answer to "AT" command till performing hard reset

[Samruddhi Jadhav]

Hi,

There can be a few reasons for this.

1) If you have tried to turn the device on/off or reset it too many times, a reset loop restriction is triggered. In order to make sure that too many signals aren't overcrowding the cellular network, the modem starts a timeout mode for 30 minutes. This loop blocks LTE attach attempts. During this, AT commands still work. Network attach is what is blocked not UART/AT. I would suggest that before powering off, put the modem in offline mode (AT+CFUN=0).

2) If the power supply is not sufficient, it can cause the voltage to decrease during a network attach. This can lead to the device hanging. 

3) Ensure on both devices that "Hardware Flow Control" is either kept on or off. A communication hang may be caused if one device is waiting for a "ready" signal but the other device isn't sending.

4) It is also possible that if the function nrf_modem_lib_init() fails, then the chip may not respond to further communication.  But, this is not a common cause.

5) I would recommend checking UART configuration and timing between the two. If nRF9160 receives concatenated AT commands due to baud rate, parity, stop bits etc. not matching or too fast commands, it may not respond as we expect.

Let me know if you have any further questions.

Best Regards,

Samruddhi