Getting +CEREG: 5,"FFFE","FFFFFFFF" while disconnected from the network

[Lukáš]

Hi,

In one of our private issues where we asked how to detect a lost cell, a Nordic engineer told us that: 

You can detect if the cell is lost from +CEREG but would not be able to detect it if this actually is about cell reselection. If +CEREG where <stat> is something else than 2 or 5 then it means the device is not in service at that moment.

However, we noticed that when we lose the signal/cell, then we receive CEREG notification with stat 5 (registered, roaming). Particularly:

+CEREG: 5,"FFFE","FFFFFFFF",9,,,"11100000","00101000"

So what is the correct procedure to detect when the modem is not attached to the network and it is not connected to any cell? Sometimes we also receive this CEREG: 4 with FFFE, so it is confusing.

 

[John]

Hmmm, after more sleepless nights testing our new hardware design, I have a theory that the error that you are seeing may be consistently reproducible and possibly overlooked during initial testing of the nRF9160.

I'd love to know what the voltage is when you are receiving this error please ?

If I'm correct, then whilst the response to +cereg is peculiar, it's almost understandable.

I think it's telling us that even if you were climbing up a ladder, beneath the cell tower, holding the nRF9160 proudly aloft in your left hand, then you are NEVER EVER going to get a connection because the voltage supplied to the modem is too low.

So, increase VDD to 4.2V and run off an AC power supply and see if the problem evaporates.

Really hope it does, because that's what I'm seeing.