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?

[Deval]

Additional information

AT+CEREG=5

OK
AT+CFUN=1

OK

+CEREG: 90
AT+CFUN?

+CFUN: 1

OK

[Michal]

Hello,

Are you able to use this SIM card with a DK?

Best regards,

Michal

[Deval]

Yes I have confirmed the SIM works with the DK

[Michal]

Are you able to measure the lines connected to the SIM card reader with a logic analyzer or an oscilloscope?

Best regards,

Michal

[Deval]

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.