Reading Messages of Modem Connected with PLC

In the latest applications modems are used with PLC for the remote control applications. Modems have found their way to be sued with PLC for better remote monitoring applications. We have already discussed as How to send Message through GSM Modem and also about the SMS through SCADA & Modem. Today we will see the AT command used for sending the message received on GSM Modem to the Terminal Equipment(TE).

AT Command for Message Transfer to TE

The indication will be sent from the network to TE when TE is active; for example, DTR signal is ON. controls the processing of unsolicited result codes specified within this command, <mt> sets the result code indication routing for SMS-DELIVERs, <bm> for CBMs and <ds> for SMS-STATUS-REPORTs. <bfr> defines the handling method for buffered result codes when <mode> 1, 2 or 3 is enabled.

If ME does not support requested item (although TA does), final result code +CMS ERROR: is returned. Test command returns the settings supported by the TA as compound values.

NOTE: Command Select Message Service +CSMS should be used to detect ME support of mobile terminated SMs and CBMs, and to define whether a message which is routed directly to TE should be acknowledged or not.

SYNTAX:- AT+CNMI= [,(mt) [,(bm) [,(ds) [,(bfr)]]]]

Now let us see the meaning of Mode, <mt>, <bm>, <ds>, and <bfr> and values associated with them.

Mode Values:-

0 -- Buffer unsolicited result codes in the TA. If TA result code buffer is full, indications can be buffered in some other place or the oldest indications may be discarded and replaced with the new receiver indications.

1 -- Discard indication and reject newly received message unsolicited result code when TA-TE link is reserved (e.g. in online data mode). Otherwise forward them directly to the TE.

2 -- Buffer unsolicited result codes in the TA when TA-TE link is reserved (e.g. in online data mode) and flush them to the TE after reservation. Otherwise forward them directly to the TE.

(mt) Value:-

0 -- No SMS-DELIVER (message to ME) indications are routed to the TE. Default.

1 -- SMS-DELIVER is stored in ME. The indication of the memory location is routed to the TE by using the unsolicited result code.

2 -- class 0, class 1 and class 3 SMS-DELIVERs are routed directly to the TE using unsolicited result code.

3 -- Class 3 SMS-DELIVERs are routed directly to TE using unsolicited result codes defined in <mt>=2. Messages of other data coding schemes result in indication as defined in <mt>=1.

(bm) Value:-
0 -- No CBM indications are routed to the TE.

1 -- The CBM is stored and an indication of the memory location is routed to the customer application using unsolicited result code: +CBMI: "BM", <index>

2 -- CBM is routed directly to the TE by using the unsolicited result code:

+CBM: <length><cr><lf><pdu> (PDU mode enabled)
or
+CBM: <sn>,<mid>,<dcs>,<page>,<pages>(Text mode) <CR><LF> <data> (text mode enabled)


(ds) Values :-
0 -- No SMS-STATUS-REPORTs are routed to the TE.

1 -- SMS-STATUS-REPORTs are routed to the TE using unsolicited result code: +CDS: <length> <CR> <LF> <pdu> (PDU
mode) or +CDS: <fo>,<mr>, [<ra>] , [<tora>], <scts>,<dt>,<st> (Text mode)

2 -- SMS-STATUS-REPORTs are stored and routed using the unsolicited result code: +CDSI: "SR",<index>


(bfr) values
Its default value is 0.

0: TA buffer of unsolicited result codes defined within this command is flushed to the TE when 1…3 is entered (OK response shall be given before flushing the codes)

1: TA buffer of unsolicited result codes defined within this command is cleared when 1…3 is entered.


We hope that CNMI AT command is clear after understanding the above things. We will discuss more about GSM Modem Communication with PLC and the AT commands used, till then you can subscribe to get all latest updates by E Mail. Subscribe to Automation-Talk by Email.

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