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FM350-GL Hardware Guide Page 38 of 67
USIM Hot-plug
The FM350 module supports the SIM card hot-plugging function, which determines whether the SIM card
is inserted or detached by detecting the SIM_DETECT pin state of the SIM card slot.
The SIM card hot-plugging function can be configured by “AT+MSMPD” command, and the description for
AT command is shown in the following table:
Default value, the SIM card hot-plugging detection function is
enabled.
The module can detect whether the SIM card is inserted or not
through the SIM_DETECT pin state.
The SIM card hot-plugging detect function is disabled.
The module reads the SIM card when starting up, and the
SIM_DETECT status will not be detected.
Note:
SIM_DETECT is active high, it can be swapped to active low by AT CMD.
USIM Design
The SIM card circuit design should meet the EMC standards and ESD requirements with the improved
capability to resist interference, to ensure that the SIM card can work stably. The following guidelines
should be noted in design:
The SIM card slot should be placed as close as possible to the module, and away from the RF antenna,
DC/DC power supply, clock signal lines, and other strong interference sources.
The SIM card slot with a metal shielding housing can improve the anti-interference ability.
In order to make sure the SIM work stably, the SIM signal quality MUST meet SIM standards “ETSI
TS 102.221 Physical and logical characteristics”. If the trace length of the SIM card signal is controlled
less than 100mm, it will be easier to meet to the SIM signal specification.
The trace length between the SIM card slot and the module should not exceed 100mm, or it could
reduce the signal quality.
The UIM_CLK and UIM_DATA signal lines should be isolated by GND to avoid crosstalk interference.
If it is difficult for the layout, the whole SIM signal lines should be wrapped with GND as a group at
least.
The filter capacitors and ESD devices for SIM card signals should be placed near to the SIM card slot,
and the ESD devices with 22 to 33pF capacitance should be used.
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