參數(shù)資料
型號： U3900BM
英文描述： Programmable Telephone Audio Processor
中文描述： 程控電話音頻處理器
文件頁數(shù)： 32/34頁
文件大?。?/td> 762K
代理商： U3900BM
U3900BM
Target Specification
Rev. A2, 25-Aug-98
7 (34)
2.1.8
Special Carrier Detect
If SCD = 0
Detect guard time = 26.4 ms
If SCD = 1
Detect guard time = 34.7 ms (26.4 ms + 10 bits of the channel seizure)
14077
Channel seizure: 010101...
Mark: 1111...
Clid Data
FSK signal
Carrier detect
Carrier lost
26.4 ms
8.3 ms
8.8 ms
(Interrupt)
SCD = 1
SCD = 0
Figure 5. Timing diagram for carrier detect in CLID mode
2.2
SCWID
14078
Mark: 1111...
Clid Data
FSK signal
Carrier lost
26.4 ms
8.8 ms
ncd (SCWID)
Carrier detect
(Interrupt)
Figure 6. Timing diagram for carrier detect in SCWID mode
The Spontaneous Call Waiting IDentifier (SCWID) part
is designed to meet:
D The Bellcore “Customer Premises Equipment
Alerting
Signal
(CAS)”:
TR-NWT-000030
&
SR-TSV-002476 specifications.
D The British Telecom “Idle State Tone Alert Signal”:
SIN227 & SIN242 specifications.
D The European Telecommunication Standard: ETS300
778-1 & ETS300 778-2 specifications.
2.2.1
Overview
SCWID is a feature that allows a subscriber who is
already engaged in a telephone call to receive caller ID
information about an incoming call.
The European Telecommunication Standard specifies
Dual-Tone Alerting Signal (DT-AS) for off-line data
transmission (on-hook) and on-line data transmission
(off-hook).
The British Telecom caller ID uses a Idle State Tone Alert
Signal in on-hook mode.
Bellcore specifies a Dual-Tone Alert Signal called CPE
Alerting Signal (CAS) for use in off-hook data
transmission. Bellcore states that the CPE should be able
to detect the CAS in the presence of near end speech. The
CAS detector should also be immune to imitation from
near and far end speech.
Note that the term “near end” refers to the end of the
telephone connection receiving the caller ID service, “far
end” refers to the other end of the connection, the Central
Office (CO).
There are two aspects of speech immunity: talk-off and
talk-down.
Talk-off is the condition where signals are falsely
detected because of imitation by speech or music. An
imitation can be caused from the far end or the near end.
Talk-down is the condition where signals are missed
because of interference from speech or music.
A CAS can be talked down only from the near end
because the far end has already been muted by the CO.
2.2.2
Description
The SCWID part is a complete dual-tone receiver
designed to detect the two frequencies 2750 Hz and
2130 Hz dedicated for this alerting function. An output
interrupt is provided to the microprocessor when
detecting the alert signal.
This device part provides all necessary filtering without
any external component.
The on-chip filtering provides excellent signal-to-noise
performance.
The dual-tone alert signal is divided into a high and a low
bandpass switched capacitor filters:
D The high alert filter is a 2750 Hz bandpass design,
with a notch placed at 2130 Hz for low frequency
rejection.
D The low alert filter is a 2130 Hz bandpass design, with
a notch placed at 2750 Hz for high frequency
rejection.
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