Specifications

Si2457/Si2434/Si2415
Rev. 0.91 19
Figure 6. Loop Current
Overcurrent Detection
The Si2457/34/15 includes an overcurrent detection
feature that measures the loop current at a
programmable time after the Si2457/34/15 goes off-
hook. This allows the Si2457/34/15 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 Si2457/34/15 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 Si2457/34/15 contains an on-chip program ROM
that includes the firmware required for the features
listed in this data sheet. In addition, the Si2457/34/15
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 Si2457/34/15 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 Si2457/34/15 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 (Si2457, pin 4)
and GND (see Table 8), the Si2457 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