SI2457-D-FS Silicon Laboratories Inc, SI2457-D-FS Datasheet - Page 18

• Manufacturer Part Number: SI2457-D-FS
• Description: IC ISOMODEM SYSTEM-SIDE 16SOIC
• Manufacturer: Silicon Laboratories Inc

Specifications of SI2457-D-FS

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Si2457/34/15/04
4.2. Command Mode
Upon reset, the ISOmodem
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 12 on page 38 and
enters data mode.
4.3. Data Mode
The Si2457/34/15/04 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 Si2457/34/15/04 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 Si2457/34/15/04 supports a V.80 synchronous
access mode of operation, which operates with an
asynchronous DTE and a synchronous DCE. See
“AN93: ISOmodem
4.6. Clocking
The Si2457/34/15/04 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, 4.9152 MHz, or 32.768 kHz 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.
through reset strapping. Refer to AN93 for details.
18
Other clock options are selected at power-up
®
Chipset Family Designer's Guide”.
®
is in command mode and
Rev. 1.3
4.7. Low-Power Modes
The Si2457/34/15/04 provides multiple low power
modes. Using the S24 S-register, the Si2457/34/15/04
can be set to automatically enter sleep mode after a
pre-programmed time of inactivity with either the DTE or
the remote modem. The sleep mode is entered after
(S24) seconds have passed since the last DTE activity,
after the transmit FIFO is empty, and after the last data
are received from the remote modem.
Additionally, the Si2457/34/15/04 can be placed in
wake-on-ring-mode using the command, AT&Z. In either
mode, the ISOmodem remains in the sleep state until
one of the following occurs:






The Si2457/34/15/04 may also be placed in a complete
powerdown
completely powers down, it can only be powered back
on via the RESET pin.
4.8. Data Compression
The modem can achieve DTE (host-to-ISOmodem)
speeds greater than the maximum DCE (modem-to-
modem) speed through the use of a data compression
protocol. The compression protocols available are the
ITU-T V.42bis and MNP5 protocols. Data compression
attempts to increase throughput by compressing the
data before actually sending it. Thus, the modem is able
to transmit more data in a given period of time.
4.9. Error Correction
The Si2457/34/15/04 ISOmodem can employ error
correction (reliable) protocols to ensure error-free
delivery of asynchronous data sent between the host
and the remote end. The Si2457/34/15/04 supports V.42
and MNP2-4 error correction protocols. V.42 (LAPM) is
most commonly used and is enabled by default.
4.10. Wire Mode
Wire mode is used to communicate with standard non-
error correcting modems. When optioned with \N3, the
Si2457/34/15/04 falls back to wire mode if it fails in an
attempt to negotiate a V.42 link with the remote modem.
Error correction and data compression are not active in
wire mode.
A 1-to-0 transition on TXD (UART mode).
A 1-to-0 transition on SS (SPI mode).
A 1-to-0 transition on CS (parallel mode).
An incoming ring is detected.
A parallel telephone is picked up.
Line polarity reversal
mode.
Once
the
Si2457/34/15/04