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M14A2A User Manual
2.4.
SIM interface
M14A2A includes an SC controller, interface pins, and a dedicated LDO (3.0 V or 1.8 V).
Since M14A2A is not equipped with a SIM socket, it must place a SIM socket on the user interface board.
M14A2A provides a UIM_DETECT input pin to detect if the SIM card is present. If the USIM card is
present, UIM_DETECT should be high. (The voltage level should be 1.8 V) If the USIM card is absent,
UIM_DETECT should be low. (The module is internally pulled down.) It was recommended to choose a
SIM socket with the Card Detect pin. If the SIM card is preset, the pin will not contact the ground and
pull up to 1.8 V through a 2 k
Ω
resistor. If the SIM card is absent, the pin will normally contact the ground.
Other types of SIM sockets which can achieve this feature are also acceptable.
A 100 nF capacitor and a 1
μF apa ito
r are placed between the UIM_VCC and Ground pins in a parallel
manner. (If the UIM_VCC circuit is too long, a larger capacitor such as a 4.7
μF
capacitor can be
employed if necessary.) Four 33 pF capacitors (0402 package is recommended.) are placed between the
UIM_VCC and Ground pins, the UIM_CLK and Ground pins, the UIM_DATA and Ground pins, and the
UIM_RESET and Ground pins in parallel to filter out interference from RF signals. (An R/C circuit on pin
UIM_CLK is optional. If there is an EMI issue on this clock signal, try to adjust these R/C values.)
We recommend taking protective measures against electrostatic discharge (ESD) near the SIM socket.
The TVS diode with a V
RWM
of 5 V and junction capacitance of less than 10 pF must be placed as close as
possible to the SIM socket, and the Ground pin of the ESD protection component must be well
connected to the power Ground pin that supplies power to M14A2A.
Figure 2.
SIM card interface circuit
