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how to interface external MCU host viaUART interface with nrf9160, with only 3 pins from UART (RD,TX,GND)

We would like to use nRF9160 has MODEM only feature, such that MCU in our product can talk to nRF9160 via UART interface.

We have found an sample application [Serial LTE Modem] that comes with nRFConnect SDK , we would need to use this application with following constraint

We have UART TX , UART RX and GND ( 3 signals ) and do not have provision for CTS/RTS or any other additional GPIO for interface MODEM(nRF9160) and our UART I/O signal TTL level is 3.3V

Is this possible to accomplish the same with the sample application [Serial LTE Modem]. 

External Com port ( 115200 bps, 8N1) , 

Pin connection between nrf9160 and 3.3v ttl-uart-usb cable connected to pc

 1. ( P0.11(RX) to usb to TTL cable (TX))

2. (P0.10(TX) to usb to TTL cable (RX))

3. Common ground 

In serial lte modem app .proj file modified to enable  Uart2 based macros and disabled the UART 0 based macro.

Note: I/O switch is kept at 3.3v side

Still couldn't get response for AT commands.

Please let me know is there is a steps to configure UART 2 with no flow control and no additional gpio .

I am using segger embedded studio.

With Best Regards,

Ilanchezhian T

  • Hi Ilanchezhian 

    Håkon is currently out of office, and I will assist in the mean time. 

    Ilanchezhian T said:
    I am confused what is COM8 in your case , is it the one of the enumerated port of Jlink ?.

    This should be one of the three comports enumerated by the nRF9160DK, yes. I will confirm this when he is available. 

    Ilanchezhian T said:
    But Anyway , If I am using it has the external host interface where instead of using the UART0 ,using UART2 I could able to successfully sleep using AT#XSLEEP=2 command and  wakeup using the port pin P0.31. This works with both Debug as well as run mode. 

    If I understand you correctly you can not get it to work if you try to use UART0 with default settings, but it works if you use UART2 and route the pins from the nRF9160DK to the external uart-ttl-usb device?

    Or are you using your own custom hardware rather than the DK?

    COM45, 46, 47 in your case should be connected to the nRF9160 on the DK, and would not be connected to the nRF9160 on your own board. 

    Best regards
    Torbjørn

  • This ticket shall be closed, As I can  interface with external GPIO and able to wakeup  UART from sleep

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