L831-EA Module Hardware User Manual
Page 31 of 43
5.5.2.2 “Normally Open” SIM Circuit Design
Referenced Circuit Design:
Figure5- 8 “Reference Design of “Normally open” SIM Card Interface
Normally Open SIM Connector:
1
）
Pull out SIM card, pin 7 and pin 8 disconnect.
2
）
Inset SIM card, pin 7 and pin 8 short-circuit .
Note:
For improving EMC performance, SIM card connector should be closed to the module.
For improving the anti-jamming capability of SIM card, please choose the SIM card socket with
masking function.
Filtering capacitor on SIM card should be closed to SIM card pin.
SIM card signal need add ESD protection (just like TVS pipe), ESD components should be closed to
SIM card pin.
SIM_CD signal connection supports hot plug, default high level is available (switch to low level is
available through AT commands). If high level is detected, it means the SIM card is inserted.
5.5.3 USIM Design Points
The design of SIM interface is very important to its own normal working and the module.
There are several design guidelines that must be followed:
The layout and routing of SIM card should be away from EMI interference source , such as RF
antenna and digital switching signals.
To ensure signal integrity, the routing length between module and SIM card should not exceed
100mm.
To avoid mutual interference, the routing of UIM_CLK and UIM_DATA signal shall keep separate.
