SI2414 SILABS [Silicon Laboratories], SI2414 Datasheet - Page 70

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

Si2456/Si2433/Si2414
the billing tone has passed, the BTE bit should be
written to 0 to return the dc termination to its original
state. It takes approximately one second to return to
normal dc operating conditions. The BTD and ROV bits
are sticky, and they must be written to 0 to be reset.
After the BTE, ROV, and BTD bits are all cleared, the
BTE bit can be set to re-enable billing tone detection.
Certain line events, such as an off-hook event on a
parallel phone or a polarity reversal, may trigger the
ROV or the BTD bits, after which the billing tone detector
must be reset. Look for multiple events before qualifying
if billing tones are actually present.
Although the DAA remains off-hook during a billing tone
event, the received data from the line is corrupted (or a
modem disconnect or retrain may occur) in the presence
of large billing tones. To receive data through a billing
tone, an external LC filter must be added. A modem
manufacturer can provide this filter to users in the form
of a dongle that connects on the phone line before the
DAA. This keeps the manufacturer from having to
include a costly LC filter internal to the modem when it
may only be necessary to support a few countries/
customers.
Alternatively, when a billing tone is detected, the host
software may notify the user that a billing tone has
occurred. This notification can be used to prompt the
user to contact the telephone company and have the
billing tones disabled or to purchase an external LC filter.
Billing Tone Filter (Optional)
To operate without degradation during billing tones in
Germany, Switzerland, and South Africa, an external LC
notch filter is required. (The Si3015 can remain off-hook
during a billing tone event, but modem data is lost (or a
modem disconnect or retrain may occur) in the
presence of large billing tone signals.) The notch filter
design requires two notches, one at 12 kHz and one at
16 kHz. Because these components are expensive and
few countries supply billing tone support, this filter is
typically placed in an external dongle or added as a
population option for these countries. Figure 13 shows
an example billing tone filter.
L3 must carry the entire loop current. The series
resistance of the inductors is important to achieve a
narrow and deep notch. This design has more than
25 dB of attenuation at 12 and 16 kHz.
70
Rev. 0.9
In-Circuit Testing
The Si2456/33/14’s advanced design provides the
system manufacturer with increased ability to determine
system functionality during production line tests as well
as support for end-user diagnostics. In addition to the
local echo, a loopback mode exists allowing increased
coverage of system components. For the loopback test
mode, a line-side power source is required. While a
standard phone line can be used, the test circuit in
Figure 1 on page 6 is adequate.
To test communication with the Si2456/33/14 across the
UART, the local echo may by used immediately after
powerup.
The DSP loopback test mode tests the functionality and
data transfer from the host to the Si2456/33/14 DSP
filters out to the DAA and hybrid, back through the DSP,
and back to the host.
This is the most comprehensive test and can be
executed via the AT&T3 command. Once the AT
command is issued, the ISOmodem goes off-hook and
Table 23. Component Values—Optional Billing
FROM
RING
Symbol
LINE
C1,C2
TIP
C3
L3
L4
Figure 13. Billing Tone Filter
3.3 mH, >120 mA, <10 Ω , ±10%
10 mH, >40 mA, <10 Ω , ±10%
Tone Filters
0.027 µ F, 50 V, ±10%
0.01 µ F, 250 V, ±10%
C1
C2
L3
Value
C3
L4
DAA
To