si2439-a-gm Silicon Laboratories, si2439-a-gm Datasheet - Page 20

• Manufacturer Part Number: si2439-a-gm
• Description: V.92 And V.34 Isomodem With Global Daa
• Manufacturer: Silicon Laboratories

Si2494/39
4.2. Command Mode
®
Upon reset, the ISOmodem
is in command mode and accepts “AT” commands. An outgoing modem call can be
made using the “ATDT#” (tone dial) or “ATDP#” (pulse dial) command after the device is configured. If the
handshake is successful, the modem responds with the response codes detailed in Table 14 on page 49 and
enters data mode.
4.3. Data Mode
The Si2494/39 ISOmodem is in data mode while it has a telephone line connection to another modem or is in the
process of establishing a connection.
Data protocols are available to provide error correction to improve reliability (V.42 and MNP2-4) and data
compression to increase throughput (V.44, V.42bis and MNP5).
Each connection between two modems in data mode begins with a handshaking sequence. During this sequence,
the modems determine the line speed, data protocol, and related parameters for the data link. Configuration
through AT commands determines the range of choices available to the modem during the negotiation process.
4.4. Fast Connect
The Si2494/39 supports a fast connect mode of operation to reduce the time of a connect sequence in originate
mode. The Fast Connect modes can be enabled for V.21, V.22, Bell103, and V.29 modulations. See AN93 for
details.
4.5. V.80 Synchronous Access Mode
The Si2494/39 supports a V.80 synchronous access mode of operation, which operates with an asynchronous
®
DTE and a synchronous DCE. See “AN93: ISOmodem
Chipset Family Designer's Guide”.
4.6. Voice Mode (+FCLASS=8)
The Si2494/39 supports the implementation of voice handset, tapeless answering machine (TAM), and
speakerphone functions when used with the Si3000 voice codec. The Si3000 provides a direct interface to most
handsets, including a variable gain microphone preamplifier, microphone bias for an electret (condenser)
microphone, digital volume control, and a speaker driver. Additional Line In/Out ports can be used with external
amplifiers to support other audio sources/destinations, such as a microphone and speaker for hands-free
operation. Very few external components are required between the handset and the Si3000. See the Si3000
Voiceband Codec with Microphone/Speaker Drive data sheet and AN93 Modem Designer’s Guide for more details
ITU-T V.253 commands are used to control operation in voice mode. Voice mode is enabled by the AT command
+FCLASS=8. The Si2494 /39 DSP provides programmable soft transmit level limiters, programmable transmit and
receive gains, sidetone gain, and programmable transmit and receive filters for frequency shaping. These features
provide a completely programmable voice implementation capable of compliance with the international standards
including TBR 38 and EIA/TIA-470.
Voice mode is typically the system’s idle state. While in this state, the ISOmodem monitors the telephone line for
various events, such as DTMF detection, caller ID, or ringing (including distinctive ring). Once an event is detected,
the ISOModem sends the host either a simple event code (a single character) or a complex event code (multiple
characters) preceded by a <DLE> character to the host. For a full list of event reports, see Table 9 on page 22. In
voice mode, the ISOmodem can generate DTMF and single tones using the +VTS command; the +VLS command
is used to enable event reporting and tone generation and to control the on/off hook state. Table 9 on page 22 lists
the events that are supported based on the +VLS state.
4.7. Clocking
The Si2494/39 contains an on-chip phase-locked loop (PLL) and clock generator to derive all necessary internal
system clocks from a single clock input. A 32.768 kHz or 4.9152 MHz crystal can be used across XTALI and
XTALO pins to form the master clock (±100 ppm max, ±25 ppm recommended) for the ISOmodem. The
32.768 kHz option can provide lower BOM costs and smaller footprint. Alternatively, a clock input of 27 MHz or
4.9152 MHz can be provided to XTALI if that clock source is available in the system. A 4.9152 MHz clock input is
the default clock option. Other clock options are selected at power-up through reset strapping. Refer to AN93 for
details.
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Rev. 1.0