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SIM908 and SIM900 have the auto baudrate detect function, can support baudrate from 1200-115200, so you can use any baudrate in this range, the first data send from SIM IC will be like random error data that can be ignored.

Basic AT Commands

  • AT - AT test
Command Description Return Result
AT+ATE1 on/off AT commands return info send either ATE0 or ATE1 -
AT+CGMI Check the module manufacturer SIMCOM_Ltd
AT+CGMM Check the module model type SIMCOM_SIM900A SIM900A
AT+CGSN Check the module IMEI, worldwide unique 869988012018905 869988012018905
AT+CNUM Check the number of current sim card, not all kinds of card support this function +CNUM:"","15902020353",129,7,4 phone number 15902020353
AT_CSUB Check module version and IC type
AT_CGMR Check module firmware version
AT+CRESET reset module
AT+CSQ check signal quality +CSQ:30,0 30 is the quality of signal, max at 31
AT+CPIN? check sim card status +CPIN:READY Sim card is found
AT+COPS? check card service provider +COPS:0,0,"CHINAMOBILE" or empty CHINAMOBILE is the service provider
AT+CREG? check network registration status
AT+CPSI? check UE system info
AT+CNMP network selection commands, 2:automatic, 13: GSM only, 38: LTE only, 48: Any modes but LTE OK
  • Check module version, vendor, name, etc -> AT+GSV, return 1418B05SIM800C24_BT, this is bluetooth version
  • check baudrate AT+IPR?, set by AT+IPR=115200, AT+IPR=0 for auto detect.

Other Commands

Basic Command Group Enquery Write Command Parameters Remark and example
AT+CMEE profile AT+CMEE? AT+CMEE=2 1: use only error number code; 2: More verbose details of errors; For #2, you can see for example: +CME ERROR: SIM not inserted (Command: ATD13725585994;)
AT+IPR profile AT+IPR? AT+IPR = 9600 9600, 115200, etc serial port baud rate
AT+CFUN profile AT+FCUN? AT+IPR = 1 0=minimum Phone Functionality, 1= Full Phone Functionality, 4=disable RF circuits Set Phone Functionality