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Using a Cellular Modem and SIM Card

Introduction​

This guide lines out how to scan and connect to a 3G phone network using TechNexion products with a SIM card slot.

Getting Started​

To follow this guide a SIM-card and a (PCIe) 3G modem is needed.

Plug in the SIM card in the SIM card slot, and the modem in the corresponding PCIe / M2 slot.

Compile a driver for your modem and boot up your system.

Scanning for Networks​

The communication with the SIM card will be performed by the modem, and controlled with old-fashioned AT-commands.

First enable the modem driver if not built-in, example driver loading could be:

# modprobe usb_wwan

or

# modprobe option

but the exact modules to load depend on the modem used.

After the modem is initialized, a USB serialk interface should appear as something like /dev/ttyUSB0 or /dev/ttyACM0.

Use a terminal emulator client for interactive communication with the modem, i.e.

# minicom -D /dev/ttyUSB0

In the terminal emulator, some usefule commands are:

  • ATI -- list device information
  • AT+COPS=? -- scan and list available phone networks
  • AT+COPS=0,2,short_name -- connects to network by its short name
  • AT^SYSINFO -- connection status

The connection status string is of the format

^SYSINFO:2,3,0,5,1,,4

, where:

  • the first number after the colon indicate the connection status; 0 = No connection, 2 = OK
  • the second is connection type; 0 = No connection, 1 = data, 2 = phone, 3 = both
  • the third number is roaming state; 0 = No roaming, 1 = roaming on
  • the fourth is service mode; 0 = No, 3 = GSM, 5 = WCDMA
  • the fifth number is SIM status; 0 = NG, 1 = OK, 2-4 = partially OK, 255 = No SIM card detected

Example session​

ATI
---------
OK
---------
AT+CFUN=1
---------
OK
---------
AT+CPIN="0000"

Some of the commands below requires to wait 2~3 mins to get response

AT+COPS=?
--------------------------------------------------------------------
+COPS: (2,"Chunghwa Telecom","Chunghwa","46692",2),(1,"TW Mobile","TWM","46697",2),(1,"Far EasTone","FET","46601",2),,(0,1,2,3,4),(1,2)
---------------------------------------------------------------------

AT+COPS=0,2, Chunghwa
---------------------
OK
---------------------

AT^SYSINFO
-------------------------------------------------
^SYSINFO:2,3,0,5,1,,4
-------------------------------------------------