Specifications

Si2404
14 Rev. 0.91
Functional Description
The Si2404 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 Si2404 accepts standard modem AT commands and
provides connect rates up to 2400 kbps full-duplex over
the Public Switched Telephone Network (PSTN). The
Si2404 features a complete set of modem protocols
including all ITU-T standard formats up to 2400 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
Si2404 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 Si2404 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 Si2404
has been designed to meet the most stringent worldwide
requirements for out-of-band energy, billing-tone
immunity, surge immunity, and safety requirements.
The Si2404 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 Si2404 also provides an
8-bit parallel port.
Digital Interface
The Si2404 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
(Si2404, 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 Si2404 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
(Si2404, pin 18) and GND (Si2404, 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 Si2404 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