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L850-GL Hardware User Manual Page 37 of 54
3.5.3 USIM Hot-Plugging
The L850 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 as shown in the following table:
AT Command
Hot-plugging
Detection
Function Description
AT+MSMPD=1 Enable
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.
AT+MSMPD=0 Disable
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.
After the SIM card hot-plugging detection function is enabled, the module detects that the SIM card is
inserted when the SIM_DETECT pin is high, then executes the initialization program and finish the
network registration after reading the SIM card information. When the SIM_DETECT pin is low, the
module determines that the SIM card is detached and does not read the SIM card.
Note:
By default, SIM_DETECT is active-high, which can be switched to active-low by the AT
command. Please refer to the AT Commands Manual for the AT command.
3.5.4 USIM Design
The SIM card circuit design shall 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 case of design:
The SIM card slot placement should near the module as close as possible, 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.
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
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