L831-EA Module Hardware User Manual
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The signal lines of SIM cards shall do some ESD protection , and it request to choose the ESD
protected components with low capacitance, such as Zener diode. Recommend the clients to use the
ESD components and the equivalent capacitance shall be less than 33pF. ESD components shall
near to SIM card interfaces while layout.
5.5.4 USIM Hot Plug
L831-EA module supports the status detection function, and this function can realize hot plug of SIM
card .
5.5.4.1 Hardware Connection
The hot plug function of SIM card needs the cooperation of SIM_DETECT signal.
SIM_DETECT is low level while no SIM card; SIM_DETECT is high level while installing SIM card.
Principle description:
1
）
For “normally closed” SIM card, as shown in Figure 5-7.SIM_DETECT signal connects Pin8 (SW2) of
U2, pull down the Pin7 (SW1) to GND. SW2 and SW1 short-circuit while SIM card is not inserted, so
SW2 is low level. SW1 and SW2 disconnect while SIM card installed, SIM_DETECT is pulled high.
2
）
For “normally open“SIM card, as shown in Figure 5-8. SIM_DETECT signal connects Pin8 (SW2) of
U2 and pull down to ground through 47Kohm resistance. Pin 7 (SW1) shall be pulled up
with4.7Kohms. SW2 and SW1 is disconnected while SIM card is not inserted, so SW2 is low level.
SW1 and SW2 is short-circuiting while SIM card installed, SIM_DETECT is pulled high.
5.5.4.2 Software Configuration
“+MSMPD” is used for setting the state detection of SIM card.
AT+MSMPD=0, state detection function of SIM card is closed. The module does not detect the
SIM_DETECT signal.
AT+MSMPD=1, state detection function of SIM card is open. Detect the SIM card if installing or not
through the SIM_DETECT Pin .
SIM_DETECT is high level, SIM card is installed, and the module registers the network automatically.
SIM_DETECT is low level, SIM card is not inserted, and the module does not register the network.
Note: The parameters of “+MSMPD” is “1” by default. SIM_DETECT is the detection signal. While the
module first power on or plug after that, SIM_DETECT will detect if the SIM card is existing or not. Just
only if the SIM_DETECT is low level, the module will cannot read SIM card.
5.6 Digital Audio
L831-EA supports digital audio I2S interface.12S interface can support normal I2S modes and data
transmission of PCM modes. The level of I2S interface signal is 1.8V.
