3 Application Interfaces
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information. When the USIM_PRESENCE is at a low level, the module determines that the
(U)SIM card is removed and does not read it.
The SIM card hot plug function can be configured by running the AT+MSMPD command. The
AT commands are described as follows.
⚫ AT+MSMPD=1, enable hot plug.
⚫ AT+MSMPD=0, disable hot plug.
⚫ AT+SIMPHASE=1, set high level detection.
⚫ AT+SIMPHASE=0, set low level detection.
RF Interference Handling
In practice, RF interference is quite normal. Here are some solutions.
⚫ Antenna coupling interference
Reason:
◦ When antenna transmits with high power, it causes direct interference to the SIM signal.
◦ When antenna transmits with high power, it is coupled to the ground, reducing the
stability of the whole system and causing indirect interference to the SIM signal.
◦ Adjust the filter capacitance value the of SIM signal.
◦ Use a longer antenna and keep it far away from the SIM card.
◦ Shield the interference signal to protect the SIM card.
◦ Pay attention to the design of the ground, especially the connectivity of SIM card,
module and the system ground.
◦ Fully ground each layer of PCB and increase holes to enhance the EMC performance
of the system.
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