Specifications

Si2457/Si2434/Si2415
16 Rev. 0.91
Functional Description
The Si2457/34/15 ISOmodem
®
is a complete
embedded modem chipset with integrated direct access
arrangement (DAA) that provides a programmable line
interface to meet global telephone line requirements.
Available in two small packages, this solution includes a
DSP data pump, modem controller, on-chip RAM and
ROM, codec, DAA, analog output, and 27 MHz clock
input.
The Si2457/34/15 accepts standard modem AT
commands and provides connect rates up to 56/33.6/
14.4 kbps full-duplex over the Public Switched Telephone
Network (PSTN). The Si2457/34/15 features a complete
set of modem protocols including all ITU-T standard
formats up to 56 kbps.
The ISOmodem provides numerous additional features
for embedded modem applications. The modem includes
full type I and type II caller ID detection and decoding for
global standards. Call progress monitoring is supported
through standard result codes. The modem is also
programmable to meet global settings. Because the
Si2457/34/15 ISOmodem integrates the DAA, analog
features, such as parallel phone detect, overcurrent
detection, and global PTT compliance with a single
design, are included.
This device is ideal for embedded modem applications
due to its small board space, low power consumption,
and global compliance. The Si2457/34/15 solution
includes a silicon DAA using Silicon Laboratories’
proprietary third-generation DAA technology. This highly-
integrated DAA can be programmed to meet worldwide
PTT specifications for ac termination, dc termination,
ringer impedance, and ringer threshold. In addition, the
Si2457/34/15 has been designed to meet the most
stringent worldwide requirements for out-of-band energy,
billing-tone immunity, surge immunity, and safety
requirements.
The Si2457/34/15 allows for rapid integration into existing
modem applications by providing a serial interface that
can directly communicate to either a microcontroller via a
UART interface or a PC via an RS-232 port. This
interface allows for PC evaluation of the modem
immediately upon powerup via the AT commands using
standard terminal software. The Si2457/34/15 also
provides an 8-bit parallel port.
Digital Interface
The Si2457/34/15 digital I/O can communicate via either
a serial UART interface with flow control or via a parallel
8-bit interface.
Selection of a serial or parallel I/O interface is
determined by the state of AOUT/INT
(Si2457/34/15,
pin 15) during the rising edge of RESET
. An internal
pullup resistor forces the default state to serial mode
operation. An external 10 kΩ pulldown resistor can be
connected to AOUT/INT
to force selection of parallel
mode (see Table 8). Configuration of pins 3, 4, 8–11,
15–18, and 22–24 is determined by this interface
selection.
Serial Interface
The Si2457/34/15 supports asynchronous serial
communication with data terminal equipment (DTE) at
rates up to 307.2 kbps with the standard serial UART
format. Upon powerup, the UART baud rate is
automatically detected using the autobaud feature. If a
pulldown resistor ≤ 10 kΩ is placed between D2
(Si2457/34/15, pin 18) and GND (Si2457/34/15, pin 6),
the DTE rate is set to a 19.2 kbps baud rate (see
Table 8).
The serial interface also provides a hardware pin, DCD
(data carrier detect), which remains low as long as the
ISOmodem is connected.
The INT
interrupt pin can be programmed to alert the
host of changes to the interrupts listed in I/O Control 0
(U70).
Autobaud
The Si2457/34/15 includes an automatic baud rate
detection feature that allows the host to start
transmitting data at any standard DTE rate from
300 bps to 307.2 kbps. This feature is enabled by
default.
Table 8. Pulldown Selector
Mode Serial I/O Parallel I/O
4.9152 MHz CLK Default Pin 15
27 MHz CLK Pin 23 Pin 11, 15
Autobaud Default
N/A
19.2 kbps DTE Pin 18
No EEPROM Default
N/A
EEPROM Pin 4