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

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

John — Sat, 15 Aug 2020 17:17:25 GMT

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.

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

ovrebekk — Mon, 06 Jul 2020 16:49:40 GMT

Hi Lukas

Sounds good, I will close the case then 🙂

Best regards
Torbjørn

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

Lukáš — Fri, 03 Jul 2020 14:51:04 GMT

Hi Torbjørn,

You overtook me with the answer :) Today morning, we had a call with your colleagues and we have clarified this issue. The resolution is, that right now we should relly on cell ID, but it will be fixed in the next mode firmware release.

Best regards,

Lukas

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

ovrebekk — Fri, 03 Jul 2020 12:39:27 GMT

Hi Lukáš

Apparently the current version of the modem is not behaving exactly like Øyvind stated in the earlier case. For the time being I would recommend looking at the cell ID instead to verify whether or not you are connected to a cell tower.

We are planning to change this in the 1.3 version of the modem firmware, so that the +CEREG command would return state 4 instead of 5 when the cell is lost.

Best regards
Torbjørn

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

Lukáš — Thu, 02 Jul 2020 13:05:04 GMT

Hi Torbjørn,

[quote userid="2116" url="~/f/nordic-q-a/63267/getting-cereg-5-fffe-ffffffff-while-disconnected-from-the-network/258110"]

How do you know that the signal to the cell tower is lost?

[/quote]

Well, the +CEREG: 5,"FFFE","FFFFFFFF" doesn't seem like a valid cell. Besides that, we also receive this:

[00:00:36.594,451] modem_at_handler: Processing notification: +CSCON: 0
[00:00:37.215,637] modem_at_handler: Processing notification: %CESQ: 255,0,255,0
[00:00:37.216,766] modem_at_handler: Processing notification: +CEREG: 5,"FFFE","FFFFFFFF",9,,,"11100000","00101000"

So I am almost sure, that we have lost the cell. However, I don't get why we are still on CEREG 5, which is also contrary to what your colleague said in another ticket.

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

ovrebekk — Thu, 02 Jul 2020 12:59:35 GMT

How do you know that the signal to the cell tower is lost?

How long after you lose the connection do you get the +CEREG notification?

An alternative way to detect if you are connected or not is to use the +CESQ command, as documented here.

If you are unable to figure out the issue it would be helpful to get a modem trace and the serial log output when the issue occurs, so we can investigate more closely what is going on.

Best regards
Torbjørn