I am struggling to get SMS in PDU mode working on the SARA N211 boards. I have it working nicely on the R410M board (which confirms that I can send on the NB-IOT bands). However, with the same command sequence to send an SMS on the N211 I don’t get it working.
In both modules I am in CGMF=0 mode (PDU). What I see when listening on the modem output is a discrepancy on the reply of the modems.
The input sent to the modems to start sending my SMS is:
As a reply, R410M gives me (hex)
41 54 2B 43 4D 47 53 3D 31 38 0D 0D 0A 3E 20 00
(literally in ascii: AT+CMGS=18 cr cr lf > space nul
As a reply on the N211 I get (hex):
0D 0A 0D 20 0A 20 3E 20 0D 0A
(literally in ascii: cr lf cr space lf space > space cr lf
The “>” is the modem being open for PDU octet sequence. When entering the sequence in the R410M and closing with “ctrl-z”, the SMS is sent sucessfully. On the N211 I get CME ERROR 50, which indicates incorrect parameters. Typically this means too many bytes, or not enough bytes entered.
I strongly suspect that the different return from the modem points in the direction of the problem (there is no local echo of the command in the N211, but especially after the input cue “>” I get already a carriage return and line feed which should not be there normally. This is a reply from the modem that seem illogical.
Does anybody have a clue about this behaviour? The sim card or network is not the issue here, since R410M indicates that by using the NB-IOT bands of our provider we CAN send an SMS.
Many thanks for your help!