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FIBOCOM NL668-AM Hardware User Manual
Page 34 of 62
Note:
The USIM_PRESENCE is in active high by default, and can be switched to active low by AT
command.
AT command
Function description
AT+GTSET=”SIMPHASE”,1
Default ,high level detect
AT+GTSET=”SIMPHASE”,0
Low level detect
Table 3-12 USIM_PRESENCE
Effective Level Switched AT command
3.5.4 USIM design requirements
SIM card circuit design shall meet EMC standards and ESD requirements, and at the same time, shall
improve anti-interference ability to ensure that the SIM card can work stably. The design needs to strictly
observe the following rules:
SIM card slot is placed as close to the module as possible, away from the RF antenna, DCDC power,
clock signal lines and other strong interference sources;
Adopt the SIM card slot with metal shield shell to improve anti-interference ability;
The length of cable from the module to the SIM card slot shall not exceed 100mm. Longer cable
reduces signal quality.
USIM_CLK and USIM_DATA signals are ground isolated to avoid mutual interference. If it is difficult
to do so, SIM signal needs to be ground protected as a set;
The filter capacitor and ESD device of SIM card signal cable are placed close to the SIM card slot.
Select 22 ~ 33pF capacitor for ESD device equivalent capacitor.
3.6 UART Interface
3.6.1 UART interface definition
NL668-AM module has two serial interfaces: the main serial interface and debug serial ports. The
following describes the main features of these two serial ports:
The main serial ports supports 4800bps, 9600bps, 19200bps, 38400bps, 57600bps, 115200bps,
230400bps, baud rate. The default baud rate is 115200bps, used for data transmission and AT command
transmission.
Debug serial port supports 115200bps baud rate for FIBOCOM debug.
The following table describes the main serial port pin.
Pin name
I/O
Pin
Description
RI
O
62
Ring indicator
DCD
O
63
Data carrier detection
CTS
I
64
Clear to send
