User's Manual

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L850-GL Hardware User Manual Page
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network registration after reading the SIM card information. When the SIM_DETECT pin is low, the
module determines that the SIM card is detachedand 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 CommandsManual for the AT command.
3.6.4 USIM Design
The SIM card circuit design shall meet the EMC standards and ESD requirements with the
improvedcapability to resist interference, to ensure that the SIM card can work stably. Thefollowing
guidelines should be noted in case of design:
The SIM card slotplacement 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 slotand 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 ESDdevices for SIM card signals should be placed near to the SIM card
slot, and the ESD devices with 22~33pF capacitance should be used.
3.7 Status Indicator
The L850 module providesthree signals to indicate the operating status of the module, and the status
indicator pinsas shown in the following table:
Pin
Pin Name
I/O
Reset Value
Pin Description
Type
10
LED1#
O
PD
System status LED, drain output.
CMOS 3.3V
23
WOWWAN#
O
PU
Module wakes upHost (AP).
CMOS 1.8V
48
TX_BLANKING
O
PD
PA Blanking output, externalGPS control
signal.
CMOS 1.8V