MC7355 MC7304 MC7804 PPP and AT commands

I’m using these devices on embedded linux, when i load the drivers I get three ttyUSBs 0 1 2.
One corresponds to the AT command interface, one corresponds to GPS data, and I cant work out what the final one is for.

My questions are as follows:

1.) What is the third tty for?

Secondly, ive been able to get a data connection using ppp on the AT command interface, however, once ppp
is up, i can no longer issue AT commands. On other sierra wireless modems, i’ve been able to use one tty with
ppp and another to issue AT commands.

2.) Is there a way to enter AT commands without interrupting PPP on the MC7304 and MC7355? Is it possible to configure the modules to run ppp on one tty and issue AT commands on another?

Thanks for any help.


  1. the 3rd interface is the Diagnostics Port.

  2. As the AT port share both AT command and PPP functionality, it is not possible to accept AT command except you terminate the PPP dialup (or vice verse).

Not sure which Linux distro/kernel you are using, but with MC73/MC78 module the wwan0 NDIS interface should be enumerate as the same time, this interface is dedicated for data session.
Please contact your distributor or FAE to obtain the SDK and driver package to make sure of this interface so you can send AT command on AT port and use NDIS for data session.

Hope it helps.