MC7455 SMS Command locks COM port

We are testing a negative test case of trying to send an SMS with a SIM card inserted that cannot send SMS messages, using AT commands.

Unfortunately when we execute the +CMGS command and are given the “>” prompt for the message, after a ^z is sent, the COM port freezes. Nothing we do can cancel the command, or get un-frozen. We can disconnect from the COM port, and re-connect fine, but no commands are accepted from this point on.

The only way to then get back into the MC7455 is a reboot of the card by powering the host off/on.

We know the SMS will not send, but we need to not cause the COM port to become unusable when trying to send an SMS that will not work. Or some way to cancel the command if it is just trying over and over again.

Thanks for the help!

An update.

I don’t see the locking anymore, perhaps was just an anaomoly with the 15 things I have going on…

But, I still have a strange issue when executing the +CMGS command. I never get a response back with the of the sent message.

This is what I see:


Two things of note:

  • The message is sent.
  • I get an > and then an OK before I can enter the PDU. Normally after the ^M for the length, it should sit at > for the PDU, and then after the ^Z, a response back +CMSG: . But I get no response either.

This is what other modems do:

> 0011000B816171184947F30000AD1941F79B8E2ECB41F4F29C0E32CBDF6D507378A3D56A21
+CMGS: 9

Obviously I am missing something, but can’t seem to sort it out.

Some more info in case it helps someone else in the future.

There seems to be an odd interaction between the GPS running, and being able to send SMS via CMSG command.

If the GPS is outputting NMEA to the NMEA port, cmsg does not behave correctly and you get no +CMSG response, and you get an “OK” before the PDU is entered (> and OK, instead of just >), which is not correct. If I execute a !gpsend=0,255 and stop all sessions, the +cmsg command works as it should.

So, easy enough to turn GPS off and on around sending SMS, but seems like there is a bug in there somewhere.

Looks like the CMGS command will eventually timeout when attempting on a SIM that cannot send SMS. But the timeout takes ~ 5 minutes. That is a long time to lock the AT channel.

Is it possible to reduce this timeout somehow?

Hi guys,
I recently bought sierra wireless MC7455 but our system is not recognizing this device. MC7345 module used to work well. I am using PCIe slot to connect MC7455 but device manager shows no sierra wireless card as detected. Is it a compatibility issue?