si2493 Silicon Laboratories, si2493 Datasheet - Page 19

• Manufacturer Part Number: si2493
• Description: V.92 Isomodem With Global Daa
• Manufacturer: Silicon Laboratories

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 40 and
enters data mode.
4.3. Data Mode
The Si2493 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 Si2493 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 Si2493 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. Clocking
The Si2493 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.
Other clock options are selected at power-up
®
is in command mode and
Rev. 1.3
®
4.7. Low-Power Modes
The Si2493 provides multiple low power modes. Using
the S24 S-register, the Si2493 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 Si2493 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 Si2493 may also be placed in a complete
powerdown mode. Once the Si2493 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.44, 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 Si2493 ISOmodem can employ error correction
(reliable) protocols to ensure error-free delivery of
asynchronous data sent between the host and the
remote end. The Si2493 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
Si2493 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
Si2493
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