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  • Case ID: 351608
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Unable to detect SIM on custom PCB and SIM VCC never goes high

Deval

I am using the SLM project with pppd and cmux for Linux on my custom board. I am able to create CMUX and communicate with the nrf 9151 using the CMUX AT port using my custom overlay (which only changes the UART pins). But I am unable to create the pppd because the SIM Card is not detected. 

When I probe the SIM VCC line I always see 0 V. On the nrf9151 DK with the same project I can see that same pin go high and the example project works. 

This is the output I see with the AT commands. 


AT+CFUN=1

OK
AT%XSIM?

%XSIM: 0,9

OK
AT+CEREG?

+CEREG: 0,90

More information. 

AT%SHORTSWVER

%SHORTSWVER: nrf91x1_2.0.2

Do I need to do any additional configuration for the SIM pins? What should I be seeing on all the SIM pins?

Parents Reply
  • 0 in reply to Michal

    Hello,

    We were able to get probing of the lines after we run AT+CFUN=1

    From our HW team:

    We also tried testing with and without a SIM card populated and the results are still the same. 
    • When issuing a command like AT+CFUN=1 to enable the modem, the SIM_1V8 goes high, the CLK line begins to PWM, and the IO line goes high but there is no other data on that line.
    • Partway through the AT+CFUN=1 response, there's a brief moment where clocking stops, IO goes low, and SIM_1V8 drops to approximately 1.3V with this "blip". 
    • When issuing a command like AT%XSIM? there is no movement on any three of these lines, including nothing on SIM_1V8. Everything stays at 0 even though we receive a %XSIM: 0,9 response on the terminal. 

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