EM7455 UIM_PWR missing


I’m developing my custom modem using the EM7455. I cannot get the sim detection using AT+CPIN? always show me the ERROR: SIM not inserted.
I have left the pin SIM_DETECT (66) floating. However the SIM VCC supply (UIM_PWR pin 36) is always low, so the sim card is not powered at all.
Current fw version:



It is OK to leave the SIM_DETECT line floating and that will indicate to the module firmware that the SIM is present. You will need to follow the Product Technical Specifications to properly bias the UIM1_PWR line with a nominal + 3 Volts. You should then return an AT+CPIN? READY.



Hi @jleitner thanks for your response. Looking at the Product technical specifications, the pin UIM1_PWR is a power output pin to connect directly to the SIM VCC supply. So it is suppose to be 1.8V or 3.0V. I have measured the voltage in te pin SIM_DETECT and it is 1.8V.



As Jon has said if you leave the SIM detect floating the unit will assume that it is connected to a SIM. On power up it will attempt the power the SIM up and detect the voltage type then initiate comms with it, if it is unable to do this then the response will come back as no SIM inserted.

All of this is automatic and pretty fast, you essentially need to leave the comms between the unit and the SIM alone and allow it to manage it so just wire it up as per the PTS and it should work.




Well, I suppose It must be a problem with the comm lines. I will check, thanks for your help


UIM voltage levels, per 3GPP specs, can be 1.8 Volts or 3 Volts. SIMs must be compliant for both voltage ranges; I believe most SIMs these days are actually at 1.8 Volts. Please follow the PTS for connecting/bias for the UIM_PWR lines and other SIM interface lines.