SimCom SIM808, Проектирование аппаратного обеспечения

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SIM808_Hardware Design_V1.00 2014.03.27 52
only can be got after the antenna tuning. Usually, matching components’ value is provided by antenna vendor, the
default value of R101 and R102 are 0
Ω , and reserve the place of C101 and C102 without soldering.
The RF test connector in Figure 50 is used for conducted RF performance test, and should be placed as close as
possible to the module’s RF_ANT pad. The traces in bold type should be treated as 50
Ω impedance controlled
line in PCB layout. For details about radio frequency trace layout, please refer to
document [9].
5 GPS Application Interface
SIM808 provide a high-performance L1 GPS solution for cellular handset applications. The solution offers
best-in-class acquisition and tracking sensitivity, Time-To-First-Fix (TTFF) and accuracy. The GPS engine
supports both fully-autonomous operations for use in handheld consumer navigation devices and other
standalone navigation systems.
The module supports GPS, QZSS, SBAS ranging (WAAS, EGNOS, GAGAN, MSAS).
The GPS NMEA information is output by serial port. The default baud rate is 115200bps.
The GPS engine is controlled by GSM engine, so when it is necessary to run GPS
， the GSM engine must be
powered on and not in SLEEP mode.
All the GPS function is controlled by AT command via serial port. The GPS functions of AT commands are listed
in the following table.
Table 37: AT Commands for GPS function
Command Description
AT+CGPSPWR GPS power control
AT+CGPSRST GPS mode reset (hot/warm/cold)
AT+CGPSSTATUS Get current GPS status
AT+CGPSOUT GPS NMEA data output control
AT+CGPSINF Get current GPS location info
AT+CGPSIPR Set GPS NMEA output UART bps
For details of these AT command, please refer to
document [1].
5.1 GPS Operating Modes
GPS has two operating modes which can be controlled by AT command.
Active mode: GPS is active as a GPS receiver. The GPS engine will automatically acquire and track GPS
satellites.
Power down mode: The GPS engine will be set into this mode by sending AT command “AT+CGPSPWR=0”. In
this mode the internal power supply for GPS will be shutdown, and the current consumption is very low. The last
position, current time and ephemeris data will be stored in the GSM host memory.