NRF9160 DK Serial LTE Modem not answering to AT commands

[RobertT]

 Hello!

 I have the NRF9160 DK set up to use UART2 and listen to AT commands from external MCU, NRF52840 DK configured to send using UART0. 

The NRF9160 set up is done, pins also connected, according to https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/applications/serial_lte_modem/doc/slm_description.html . The code on it is from NRF Connect SDK 1.4.0., serial lte modem application. 

 The NRF52840 code is according to https://github.com/NordicPlayground/nRF52-clients-for-serial-LTE-modem/blob/master/slm_client/ . 

I have tried CONFIG_SLM_NULL_TERMINATION  and also CONFIG_SLM_CR_LF_TERMINATION . 

Somewhere bellow you can see the RTT from NRF52840 and the terminal from NRF9160.

The AT commands sent have no answer / no feedback, expecting something like when I use the LTE Link Monitor where I see an OK sent back, or when I see the modem ICON turning green.

Please advise what steps did I miss.

Thank you!

 

partial RTT log for NRF52840 : 

==========

00> <info> app: SLM client started.
00>
00> <error> app: NRF_SERIAL_EVENT_DRV_ERR(0x0000000C)
00>
00> <info> app: UART SEND, length:9
00>
00> <info> app: 41 54 2B 43 46 55 4E 3D|AT+CFUN=
00>
00> <info> app: 31 |1
00>
00> <info> app: UART SEND, length:2
00>
00> <info> app: 0D 00 |..
00>
00> <info> app: UART SEND, length:2
00>
00> <info> app: 41 54 |AT
00>
00> <info> app: UART SEND, length:2
00>
00> <info> app: 0D 00 |..
00>
00> <info> app: UART SEND, length:2
00>
00> <info> app: 41 54 |AT
00>
00> <info> app: UART SEND, length:2
00>
00> <info> app: 0D 00 |..
00>
00> <info> app: UART SEND, length:8
00>
00> <info> app: 41 54 2B 43 46 55 4E 3F|AT+CFUN?
00>
00> <info> app: UART SEND, length:2
00>
00> <info> app: 0D 00 |..
00>
00> <info> app: UART SEND, length:8
00>
00> <info> app: 41 54 2B 43 46 55 4E 3F|AT+CFUN?
00>
00> <info> app: UART SEND, length:2
00>
00> <info> app: 0D 00 |..
00>
00> <info> app: UART SEND, length:9
00>
00> <info> app: 41 54 2B 43 46 55 4E 3D|AT+CFUN=
00>
00> <info> app: 30 |0
00>
00> <info> app: UART SEND, length:2
00>
00> <info> app: 0D 00 |..
00>
00> <info> app: UART SEND, length:9
00>
00> <info> app: 41 54 2B 43 46 55 4E 3D|AT+CFUN=
00>
00> <info> app: 30 |0
00>
00> <info> app: UART SEND, length:2
00>
00> <info> app: 0D 00 |..
00>
00> <info> app: UART SEND, length:2
00>
00> <info> app: 41 54 |AT
00>
00> <info> app: UART SEND, length:2
00>
00> <info> app: 0D 00 |..
00>
00> <info> app: UART SEND, length:9
00>
00> <info> app: 41 54 2B 43 46 55 4E 3D|AT+CFUN=
00>
00> <info> app: 31 |1
00>
00> <info> app: UART SEND, length:2
00>
00> <info> app: 0D 00 |..
00>
00> <info> app: UART SEND, length:8
00>
00> <info> app: 41 54 2B 43 46 55 4E 3F|AT+CFUN?
00>
00> <info> app: UART SEND, length:2
00>
00> <info> app: 0D 00 |..
00>
00> <info> app: UART SEND, length:2
00>
00> <info> app: 41 54 |AT
00>
00> <info> app: UART SEND, length:2
00>
00> <info> app: 0D 00 |..
00>
00> <info> app: UART SEND, length:9
00>
00> <info> app: 41 54 2B 43 46 55 4E 3D|AT+CFUN=
00>
00> <info> app: 30 |0
00>
00> <info> app: UART SEND, length:2

======

Terminal log for NRF9160: 

[Heidi]

Hi!

Are you using the nRF52840 DK?

Have you set both CONFIG_SLM_GPIO_WAKEUP and CONFIG_SLM_CONNECT_UART_2 in the application flashed to the nRF9160 DK?

Are you pushing the buttons to send the AT command or have you modified the sample to send them? If it's the latter, could you provide me with the modifications so I can take a look?

Lastly, do you have access to an oscilloscope or logic analyzer to check whether something is being sent over the lines between the nRF52840 DK and the nRF9160 DK?

Best regards,

Heidi

[RobertT]

Hello, Heidi!

 - > both of them are set, CONFIG_SLM_GPIO_WAKEUP and CONFIG_SLM_CONNECT_UART_2.

 - > yes, pushing the buttons.

 - > I  see bits sent on the osci . 

 All the best,

Robert.

[Heidi]

Okay.

So the nRF9160 isn't receiving them for some reason. It's trivial, but have you double-checked the connection lines?

nRF52 Series DK	nRF9160 DK
UART TX P0.6	UART RX P0.11
UART RX P0.8	UART TX P0.10
UART CTS P0.7	UART RTS P0.12
UART RTS P0.5	UART CTS P0.13
GPIO OUT P0.27	GPIO IN P0.31

Have you set the GPIO output level on the nRF9160 DK to 3V (SW11)?

[RobertT]

Hello, Heidi!

 Sorry for the late reply. I just had to focus on some other part of the project. Yes, the nRF9160 DK is set to 3V. The electrical connections are set as you described.

 I will only close the ticket now since I will need to come back sometime in the near future on this and do not want to take more of your time.

Will be back soon.

All the best, 

Robert.