I have a test circuit with a RM520 modem, the modem fails to see that a SIM is plugged in.
I have measured the voltage at the USIM_DET (pin66) and I see a voltage (on the oscilloscope) that swings between 0V and ~1.8V where when the SIM is plugged in the voltage is ~1V8, when unplugged the voltage is zero. I have checked I am on the correct slot using AT+QUIMSLOT = 1. When I check the SIM Status I get AT+QSIMSTAT?
+QSIMSTAT: 1,0
Checking SIM detect I get:
AT+QSIMDET?
+QSIMDET: 1,1
Why doesn’t the modem see the SIM, as a result the modem does not power up the SIM, in other words I do not see a voltage on the USIM1_VDD (pin 36) line.
ANy help much appreciated, thanks.
Dear @fuguiwang-Q
Please help to check.
According to your description, the SIM’s hot plug detection function has been turned on and the high level is valid. You can set AT+QSIMDET=0 to disable hot plug detection, and then restart to confirm whether the SIM card can be used normally.
If it can be used normally, it should be caused by an error in the SIM’s hot plug detection logic.
If the hot plug detection function is disabled and the SIM card still cannot function properly, it is recommended to use an oscilloscope to measure all signal pins of the SIM card during the module startup process. All signal pins will have at least a brief high-level output. If all measurements have normal outputs, it is necessary to confirm the SIM card or provide a schematic and PCB to confirm if the design is correct.
