Modicon M221 and SR2MOD03: Why SMS are not received properly =>CommError=255 / OperError=17 ?

When using the SMS feature on M221 controllers with the new model (HW1103B4) of the SR2MOD03 modem (connector 15 pins), the following error codes could be returned when receiving a SMS

%SEND_RECV_SMSi.CommError=255
%SEND_RECV_SMSi.OperError=17

Error code meaning:

17 (00000011 hex)

MessageNotMatching

The received message does not match with any message in the command list. Issued only if the sender phone number matches an entry in the list of approved numbers (whitelist).

This comes from a limitation of the new model (HW1103B4) of the SR2MOD03 modem.
Indeed when using this model, if the length of the received SMS is higher than 20 characters then the message is cut and so it no longer matches with the defined message in the command list.

This issue appears due to the usage of the following AT commands in the init command:
CNMI=0,2,0,0,0 : SMS-DELIVER are routed directly to the equipement
CMGF=0 : PDU Mode

NOTE:
This limitation is not observed with M241/251 and M262 controllers as they work in Text Mode (CMGF=1).
M221 doesn’t support Text Mode. Only PDU Mode (CMGF=0)  is supported.

Released for:Schneider Electric Australia