Connection Sequence


I’m currently making a VxWorks driver for the MC7700 modem and I am trying to figure out what the correct sequence of AT command is in order to establish a data connnection.

The AT interface is implemented and the DirectIP interface is partly implements.

I use the following sequence to establish a connection but have yet to send a successful ping.


I then create the network device and use at!scpaddr=1 to retrieve the IP address.

Am I missing a command?

Also, as an experiment, I used Sierra Aircard Watcher in Windows to establish a successful data connection and switched the modem to my VxWorks dev system. After creating the device in ifconfig and setting the routes I was able to successfully ping Google.




command will reboot the modem - and this will take some time to complete. So if you’re firing off the


immediately after the +CFUN then your commands are probably being missed by the modem.
Something like this may be better:

AT+CFUN=1  // force reboot
AT // Send AT until you get an OK response which indicates the modem is back up
AT+CPIN? // test for sim ready state - or input the SIM PIN if required
AT+CREG?  // repeat this until you get the appropriate +CREG response indicating the network is ready
AT+CGATT=1 // etc

You should also be waiting for a response to the command - OK, ERROR or results - before sending the next command. You might also want to try sending


as the first command AFTER the reboot - this gives numeric codes for error messages which makes debugging easier.

Hope this helps somewhat.
ciao, Dave

AT!SCACT=1,1 works fine for Direct IP modem ( PIS=0x68A3), but seems it doesn’t work for QMI modem (PID=0x68A2). I am not sure the AT!SCACT command is a valid command to activate PDP context or not - I always got error with that command from QMI modem:


My module has been registered successfully with home network -

+CREG: 0,1


How (steps) can we activate PDP context for QMI modem (MC77xx, MC7354) to start data connection ?


I do wait for a response after each command I send and get OK for most of them.

I assume that if the following commands returns OK and I get a valid IP address, it means that the connection was successful and the modem is ready to transmit and receive data.


Am I correct or am I missing something?

Is there a command that I can use to verify if I have a valid connection?

Is it possible, that the modem has a valid connection but I need to send some kind of special command to the directIP interface to initialize it?

Your sequence is correct to activate PDP context - if you want to pass traffic through Direct IP interface, you need to pass the assigned IP from carrier to DIP interface via dhclient or ip route command

Make sure your modem has got IP address
!SCACT: 1,1

!SCPADDR: 1,“”


After that, start dhclient on direct ip interface (dhclient wwan0) -

  • check wwan0 interface - make sure it got the same IP address as from AT!SCPADDR=1 command
  • set any route you wish through wwan0 interface
  • should be able to send traffic via wwan0 interface

I don’t think Sierra has implemented any AT command for that, so you have to use QMI. Send a QMI_WDS_START_NETWORK_INTERFACE command.