Specifications

Si2404
Rev. 0.91 17
Figure 6. Loop Current
Overcurrent Detection
The Si2404 includes an overcurrent detection feature
that measures the loop current at a programmable time
after the Si2404 goes off-hook. This allows the Si2404
to detect if it is connected to an improper telephone line.
The overcurrent detection feature may be enabled by
setting the OCDM bit (U70, bit 11). OHT (U77, bits 8:0)
sets the delay after off-hook until the loop current is
measured. See “AN93: Modem Designer’s Guide” for
details.
Global Operation
The Si2404 chipset contains an integrated silicon direct
access arrangement (Silicon DAA) that provides a
programmable line interface to meet international
telephone line interface requirements. “AN93: Modem
Designer’s Guide” gives the DAA register settings
required to meet international PTT standards.
Additionally, the user-access registers (via the AT:U and
AT:R commands) may be programmed for country-
specific settings, such as dial tone, ring, ringback, and
busy tone. See “AN93: Modem Designer’s Guide” for
complete details.
Firmware Upgrades
The Si2404 contains an on-chip program ROM that
includes the firmware required for the features listed in
this data sheet. In addition, the Si2404 contains on-chip
program RAM to accommodate minor changes to the
ROM firmware. This allows Silicon Labs to provide
future firmware updates to optimize the characteristics
of new modem designs and those already deployed in
the field. See “AN93: Modem Designer’s Guide” for
complete details.
Codec Interface
In order to support a full range of voice and data
applications, the Si2404 includes an optional serial
interface that connects to an external voice codec
(Si3000). See “AN93: Modem Designer’s Guide” for
complete details.
EEPROM Interface
The Si2404 supports an optional serial peripheral
interface (SPI) bus serial EEPROM Mode 3 with a 16-bit
(8–64 kbit range) address. Upon powerup, if a pulldown
resistor ≤10 kΩ is placed between D6 (Si2404, pin 4)
and GND (see Table 8), the Si2404 attempts to detect
an EEPROM. The EEPROM is intended first for setting
custom defaults, second for automatically loading
firmware upgrades, and third to allow for user-defined
AT command macros for use in custom AT commands
or country codes. See “AN93: Modem Designer’s
Guide” for complete details.
0 3 6 9 12 15 18 21 24 30 33 36 39 42 45 48 51 54 57 60 63 66 69
72
140
75 78 81 84 87 90 93
Loop Current
(mA)
LVCS
BITS
27
Overload
0
5
10
15
20
25
30
CTR21 only