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Si2400
14
Rev. 1.3
5. Functional Description
The Si2400 ISOmodem is a complete modem chipset
with integrated direct access arrangement (DAA) that
provides a programmable line interface to meet global
telephone line requirements. Available in two 16-pin
small outline packages, this solution includes a DSP data
pump, a modem controller, an analog front end (AFE), a
DAA, and an audio codec.
The
modem,
which
accepts
simple
modem
AT
commands, provides connect rates of up to 2400 bps,
full-duplex over the Public Switched Telephone Network
(PSTN) with V.42 hardware support through HDLC
framing. To minimize handshake times, the Si2400 can
implement a V.25-based fast connect. The modem also
supports the V.23 reversing protocol and standard alarm
formats including SIA.
The Si2400 ISOmodem provides numerous features for
embedded modem applications including caller ID
detection and decoding for the US, UK, and Japanese
caller ID formats. Both DTMF decoding and generation
are provided on chip as well. Call progress is supported
both at a high level through echoing result codes and at a
low level through user-programmable biquad filters and
parameters such as ring period, ring on/off time, and
dialing interdigit time.
This device is ideal for embedded modem applications
due to its small board space, low power consumption,
and global compliance. The Si2400 solution integrates a
silicon DAA using Silicon Laboratories’ proprietary
capacitive isolation technology. This highly integrated
DAA can be programmed to meet worldwide PTT
specifications for ac termination, dc termination, ringer
impedance, and ringer threshold. The DAA also can
monitor line status for parallel handset detection and for
overcurrent conditions.
The Si2400 is designed for rapid assimilation into existing
modem applications. The device interfaces directly
through a UART to a microcontroller. The Si2400URT-
EVB connects directly to a standard RS-232 interface.
This allows for PC evaluation of the modem immediately
upon powerup via HyperTerminal or any standard
terminal software.
The
chipset
can
be
fully
programmed
to
meet
international telephone line interface requirements with
full compliance to FCC, CTR21, JATE, and other country-
specific PTT specifications. In addition, the Si2400 has
been designed to meet the most stringent worldwide
requirements
for
out-of-band
energy,
billing-tone
immunity, lightning surges, and safety requirements.
The Si2400 solution needs only a few low-cost discrete
components to achieve global compliance. See
Figure 3Table 10. Selectable Configurations
Configuration
Modulation
Carrier
Frequency (Hz)
Data Rate
(bps)
Standard
Compliance
V.21
FSK
1080/1750
300
Full
V.221
DPSK
1200/2400
1200
Full
V.22bis1,2
QAM
1200/2400
2400
No retrain
V.23
FSK
1300/2100
1200/75
Full; plus reversing
(Europe)
V.23
1300/1700
600/75
Bell 103
FSK
1170/2125
300
Full
Bell 212A
DPSK
1200/2400
1200
Full
Security
DTMF
—
40
Full
SIA—Pulse
Pulse
—
Low
Full
SIA Format
FSK
1170/2125
300 half-duplex
300 bps only
Notes:
1. The V.22 and V.22bis standards refer to V.14 DTE (UART) configurations. The Si2400 does not support V.14 breaks.
In order to support overspeeding by the remote modem, the Si2400 DTE speed must be greater than the modem
(line) data rate.
2. The Si2400 only adjusts its DCE rate from 2400 bps to 1200 bps if it is connecting to a V.22-only (1200 bps only)
modem. Because the V.22bis specification does not outline a fallback procedure, the host should implement a
fallback mechanism consisting of hanging up and connecting at a lower baud rate. Retraining to accommodate
changes in line conditions which occur during a call must be implemented by terminating the call and redialing.