Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 150)

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150 Rev. 1.3
To enable the SMS features on the ISOmodem, the host must send AT+FCLASS = 256 to the modem prior to
handling an SMS call. The host can then dial or answer an SMS call using ATDTxxxx; (where xxxx is the number to
be dialed), or ATDT; respectively. Note the semicolon at the end of the command, which places the modem into
command mode immediately after dialing and returns OK. The host can then prepare the modem for transmitting or
receiving SMS data.
To receive Protocol 1 or Protocol 2 data, the host must send AT+FRM = 200. This causes the modem to return to
data mode silently, listening for data from the remote SMS server. If the modem detects a valid Protocol 1 or
Protocol 2 packet, it responds with a CONNECT 1 or CONNECT 2 message respectively, followed by the SMS
message (without channel seizure and mark). When the carrier stops, the modem returns to command mode and
responds with OK.
To transmit Protocol 1 or Protocol 2 data, the host must send AT+FTM = 201 or AT+FTM = 202. This causes the
modem to return to data mode and wait silently until data are received from the host processor for transmission.
Once data are received from the host, the modem transmits the proper number of channel seizure and mark bits
followed by the data it received from the host. After the modem has begun transmitting, it will send marks when it
does not have data to send and will continue to do so until the host escapes to command mode.
The content of the data message is entirely up to the host including any checksum or CRC. ETSI ES 201 912
describes two standard data and transfer layers that are commonly used. SMS typically relies on caller
identification information to determine if the call should be answered using an SMS device or not. Refer to "6.3.
Caller ID" for more information on how to configure the modem for Caller ID detection.
AT+FRM = 200 Returns to data mode prepared
to receive an SMS message.
AT+FTM = 201 Returns to data mode prepared
to transmit an SMS Protocol 1
message.
AT+FTM = 202 Returns to data mode prepared
to transmit an SMS Protocol 2
message.
Table 98. SMS Commands