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L811-EB Hardware User Manual Page 30 of 47
3.5.3
USIM Hot-Plugging
The L811-EB module supports the SIM card hot-plugging function, which determines whether the SIM
card is inserted or detached by detecting the SIM_CD 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 as follows:
AT Command
Detection of SIM Card
Hot-plugging Function
Function Description
AT+MSMPD=1 Enable
Default value, the SIM card hot-plugging detection function
enabled.
The module can detect whether the SIM card is inserted or
not through the SIM1_CD pin state.
AT+MSMPD=0 Disable
The SIM card hot-plugging detect function disabled.
The module reads the SIM card when starting up, and
SIM_CD status will not be detected.
After the SIM card hot-plugging detection function is enabled, when the SIM1_CD is high level, the
module detects that the SIM card is inserted, and then executes the initialization program, and finish the
network registration after reading the SIM card information. When the SIM1_CD is low level, the module
determines that the SIM card is detached, and does not read the SIM card.
Note:
By default, SIM_CD is active-high, which can be switched to active-low by 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 SIM1_CLK and SIM1_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.