SI2414 SILABS [Silicon Laboratories], SI2414 Datasheet - Page 38

• Manufacturer Part Number: SI2414
• Manufacturer: SILABS [Silicon Laboratories]

Si2456/Si2433/Si2414
Overcurrent Detection
The Si2456/33/14 includes an overcurrent detection
feature
programmable time after the Si2456/33/14 goes off-
hook. This allows the Si2456/33/14 to detect if it is
connected to an improper telephone line (such as a
digital PBX) that may damage the DAA. 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. If OCDM is
enabled and excessive current is detected, the Si2456/
33/14 will send the “X” result code and trigger an
interrupt by asserting the INT pin (or set the INT bit in
parallel mode). After an interrupt, the host should issue
the AT:I command to verify the OCD interrupt and clear
OCD bit (U70, bit 3). The host should hang up the
modem with the ATH command immediately after an
overcurrent is detected in order to avoid damaging the
DAA.
In the CTR21 mode of operation (see Table 19), the
overcurrent detection can trip unnecessarily for loop
current values greater than 55 mA. Therefore, if the
ISOmodem is in CTR21 mode and an overcurrent
condition is detected, the host should switch the
ISOmodem into FCC mode and check the LVCS
register for a valid overcurrent value equal to 0x1F.
Global Operation
The Si2456/33/14 chipset contains an integrated silicon
direct access arrangement (Silicon DAA) that provides a
programmable line interface to meet international
telephone line interface requirements. Table 19 on
page 39 gives the DAA register settings required to
38
that
measures
LVCS
BITS
30
25
20
15
10
5
0
0 3 6 9 12 15 18 21 24
the
loop
current
CTR21 only
27
Figure 8. Loop Current
30 33 36 39 42 45 48 51 54 57 60 63 66 69 72
at
Rev. 0.9
a
Loop Current
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. Table 21 on page 42 contains a listing of
these U-register settings for many countries. Additional
settings may easily be implemented by following the U-
register descriptions.
Firmware Upgrades
The Si2456/33/14 contains an on-chip program ROM
that includes the firmware required for the features
listed in this data sheet. In addition, the Si2456/33/14
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.
The firmware upgrade (provided by Silicon Labs) is a
file loaded into the Si2456/33/14 after a reset using the
AT:P command. Once loaded, the upgrade status can
be read using the ATI1 command to verify the firmware
revision number. The entire firmware upgrade in RAM is
always cleared on reset. To reload the file after a reset
or powerdown, the host simply rewrites the file using the
“AT:P” command. (See Table 11 on page 23.)
A CRC can be run on the file loaded into on-chip RAM,
with the AT&T6 command to verify that the upgrade was
correctly written to the on-chip memory. The CRC value
obtained from executing the AT&T6 command should
match the CRC value provided with the upgrade code.
(mA)
75 78 81 84 87 90 93
Overload
140