HL8548 - $CSQ Always returning 99 after no signal


If the device is blocked from getting signal, it will not acquire a signal again. CSQ is always returning 99,99 in this case and was tested for up to 5 minutes without restarting the radio. This is a showstopper for our application.

This is running FW 5.5.23

Place the device into a something that can block RF completely. We used an ESD bag [instead of an RF box which still had some signal (CSQ returned 1,99 typically in the box). In the bag, we were able to get it to 0 or 99. Taking it out after the 0 or 99, CSQ never improved even though it was in free air at that point.

What is the proper sequence after having no RF? Should we try using CGATT in hopes of getting a connection? :cry:

More details. If COPS=0 is ABORTED, it seems CSQ ALWAYS comes back as 99,99

What is this cause, is it a bug in the COPS command when the network is low? Should ABORTED be an unacceptable response putting the radio in a funky state?



Assuming the unit is set to at+cops mode 0, you should avoid setting it to 0 again as it can cause unforeseen side effects. If it is set to 0 then the correct procedure should be to leave it to re acquire the network, the algorithms are designed to do this as fast as possible. How long are you leaving after the unit has been taken out of the bag to re acquire the network? It should be pretty quick to see it.

Does performing a reset help? Because the unit resets so quickly it might be faster than the below although I would question why it does not re attach first of all.

If you want to take an active role and force a scan for which you can see the results then you could try sending at+cops=? which forces a scan across all technologies and bands that are enabled, this can take a couple of minutes to complete depending on how many cells the unit can see (if it can see a lot then it has to listen to all of them).




Hi Matt,
I have doubts about this, in old FW of Sierra this COPS command never gave me problems and only now that I change FW I’m having problems giving Cops=0 2 times, did you read about this only one time cops=0 in the datasheet in other documentation ?
Thanks, Javier



Not sure I entirely understand your post. I am speaking from experience here.




To wrap this one up. I believe the issue was a result of calling CGATT=0. Prior to a few months back, I thought we would still get RSSI even if not attached. It seems like that is not the case and that RSSI comes back as 99 once CGATT=0 is called.



Generically speaking if a unit cannot find a network it is unable to attach to then it will enter emergency mode and camp on the strongest signal so this is what you would be seeing, not necessarily the network you may or may not be attaching to if you inserted a SIM Card.




What is the proper sequence of commands to get out of the emergency camp mode?



You don’t, you either turn the radio off (at+cfun=0) or insert a SIM card and reboot the unit at which point it will power up try to attach to all of the networks around it, if it cannot then it will camp on the strongest one periodically scanning to see if it can find a network it can attach to.

What do you want it to do?




Hmm, I want it to do the periodic scan and find a valid network…but it does not appear to do that. Seems power cycling is the only option as the SIM card is installed in the device.



So just to be clear on the procedure. You do the following.

  1. Power device up with a valid SIM card in it.
  2. Attaches to the network.
  3. It loses the network and you see signal strength or not? Is there some form of network at this point?
  4. Goes back into range of a network it should be able to attach to but it does not? How fast are you expecting this to happen?




Process is correct.

  1. I do see signal strength. The previous 24 hours it was shielded from RF and was not seen to connect in that period. Removing it from the RF Shield, I expected it to connect. Looking at the radio commands of CGATT=1 and $CSQ I saw it report OK, Attached, valid RSSI and the operator matched our network operator. However, our SIM portal for the operator showed no connection since prior to shielding it from RF.

We left the device operating as usual for over two hours. It attempts to connect every 10 minutes without power cycling the radio. At this point, I would have expected it to actually connect sometime within the following hour, if not 5 hours, which it did not.


So in point 3 above the CREG and CGREG status was 1 or 5? If this is the case then as far as the unit is concerned it is attached as the correct signalling has been carried out. Is the unit able to carry out an IP connection?

I would suggest that the operator portal lag for updating status is significant if the answer to the above two questions is yes.