Generally, GSM Modem supports an "at + cnmi" command to set how to handle a short message when it arrives-only stored in the specified memory (easy to lose/non-easy to lose) medium; store the data before notifying the Te; Forward the data directly to the Te.
At + cnmi command syntax: At + cnmi = <mode>, <Mt>, <BM>, <DS>, <BFR> <mode> control the way the notification Te is sent. 0 -- first cache the notification and then send it according to the value of <Mt>. 1 -- notify the Te when the data line is idle. Otherwise, the Te is not notified. 2-when the data line is idle, notify te directly; otherwise, the notification will be cached and sent again when the data line is idle. 3 -- directly notify te. When the data line is occupied, the notification te message will be transmitted together. <Mt> set the content of the short message storage and notification te. 0 -- the received short messages are stored in the default memory location (including class 3), and Te is not notified. 1 -- the received short messages are stored in the default memory location and sent to te (including class 3 ). Notification format: + cmti: "SM", <index> 2 -- for short messages of Class 2, store them on the SIM card and send a notification to te. For other classes, forward the short message directly to te: + CMT: [<alpha>], <length> <CR> <LF> <PDU> (PDU mode) or + CMT: <OA>, [<alpha>,] <SCTS> [, <tooa>, <fo>, <pid>, <DCS>, <SCA>, <Tosca>, <length>] <CR> <LF> <DATA> (text mode) 3 -- for short messages of Class 3, it is directly forwarded to te, the same as <Mt> = 2; for other classes, the same as <Mt> = 1. <BM> set Cell Broadcast 0 -- Cell Broadcast not notification 2 -- New Cell broadcast notification, + CBM:; length; CR; LF; PDU; 3 -- cell broadcast notification in class3 format, use Bm = 2 format <DS> Status Report 0 -- Status report not notification 1 -- New Status Report Notification, return: + CDS :; length; CR; LF; PDU; 2 -- if the new status report is stored in me, + cdsi:; MEM;,; index; is returned; <BRF> 1 -- always 1. Because the SIM card has only 10 thousand to 0.1 million reads and writes and 10-15 short messages are stored, it takes some time to read and write short messages on the SIM card, therefore, it is best to send short messages directly to the Te terminal without reading/writing through the SIM card. You can set at + cnmi =, 1 ps. the concept of Short Message class: according to the specified storage location, short messages are divided into four categories of class0-3, you can also do not specify the class (no class), by the mobile device according to the default settings Processing, stored in memory or SIM card. In the TP-DCS bytes of the tpdu, The bit7-bit4 indicates the class to which the message belongs when the bit1-bit0 is 00x1, 1111. 00 -- Class 0, which can be directly displayed. 01 -- class 1, which is stored in me memory by default. 02 -- class 2, stored in SIM card. 03 -- class 3, which can be directly transmitted to the terminal device TE. The default short message is stored in the SIM card, and no other short messages are usually stored in the SIM card. You can reference this article through this link: http://yiyio77.bokee.com/tb. B? Diaryid = 12697534
