Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 149)

AN93
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6.3.5. DTMF Caller ID
DTMF Caller ID is supported in the Si2493/57/34/15/04 Revision D or above and Si2494/39 Revision A or above.
DTMF Caller ID detection is needed to provide complete CID support for Brazil, China and other countries. The
ISOmodem detects the preamble and start code (0x41, or ASCII 'A'), then echoes CIDM to the host. The
ISOmodem assembles the rest of the characters in the message and sends them to the host. It detects the stop
code (0x44, or ASCII 'D') and proceeds with the rest of the call processing.
For ISOmodems that support voice mode, detection of DTMF CID is done automatically in +FCLASS = 8 mode
after being enabled by a “+VLS = 14” command. The user can also enable FSK CID with the AT+VCID and
AT+VCDT commands. This gives simultaneous support of DTMF and FSK modes.This is useful in countries like
Brazil, China and Taiwan, where the use of DTMF or FSK varies from region to region.
6.4. SMS Support
Short Message Service (SMS) allows text messages to be sent and received from one telephone to another via an
SMS service center. The ISOmodem provides a flexible interface that can handle multiple SMS standards. This
flexibility is possible because most of the differences between standards is handled by the host in the data stream
itself. The ISOmodem performs the necessary data modulation and provides two options for message packet
structure (Protocol 1 and Protocol 2, as defined in ETSI ES 201 912). The rest of the data link layer and transfer
layer are defined by the host system. The ISOmodem uses a V.23 half-duplex modulation to transmit and receive
the data over the PSTN. Protocol 2 differs from Protocol 1 in that a packet is preceded by a 300-bit long channel-
seizure preamble. ETSI ES 201 912 describes the other differences between Protocols 1 and 2, but the host
processor handles these when structuring the data within the packet.
Four commands control the behavior of the SMS feature, as described in Table 98 below:
Table 95. Japan Caller ID
Command Function
AT+VCID = 1 Enables Caller ID.
AT+VCDT = 3 Selects Japan CID mode.
Table 96. Protocol 1
80 bits of mark (constant ones) Message
Table 97. Protocol 2
Channel seizure (300-bit
stream of alternating ones
and zeroes)
80-bit stream
of ones
Message
Table 98. SMS Commands
Command SMS Feature Behavior
AT+FCLASS = 256 Prepares the modem for
handling SMS calls.
ATDT; Goes off-hook and returns to
command mode. If a phone
number is provided, it is dialed
prior to returning to command
mode.