參數(shù)資料
型號(hào)： 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(yè)數(shù)： 30/34頁(yè)
文件大?。?/td> 762K
代理商： U3900BM
U3900BM
Target Specification
Rev. A2, 25-Aug-98
5 (34)
2
Class Function
The U3900BM includes a class function Calling Line
IDentification (CLID) for on-hook and Spontaneous Call
Waiting IDentifier (SCWID) for off-hook status.
2.1
CLID
CLID is designed to demodulate CCITT V23 and BELL
202 (1200 bauds FSK asynchronous data) and is
compatible
with
both
formats
without
external
intervention. It fulfils the CS B14-10W requirements.
The main feature of this part is to provide, for the user,
information about the caller before answering the call.
The information is a DATA message sent from the Central
Office (CO) to the CPE during the silent interval, and
after the first ringing burst.
2.1.1
Description
On the receive side, the received signal coming from
CLI1 and CLI2 first goes to an antialiasing filter after the
differential op-amp.
The next section is a bandpass filter composed of an FSK
filter composed of a fifth order high-pass followed by a
third order low-pass filter. The low-pass and high-pass
cut-off frequencies are about 300 Hz and 3400 Hz
respectively.
2.1.2
Carrier Detect
The carrier detect provides an indication (to the micro-
processor with an interrupt request) of the presence of a
signal in the FSK band. It detects a sufficient amplitude
signal at the output of the FSK bandpass filter.
Note that signals such as speech or DTMF tones also lie
in the FSK frequency band and the carrier detect may be
activated by
these
signals.
The
signals
will
be
demodulated and presented as DATA. To avoid false
DATA detection, a command bit is used to disable the
demodulator when no FSK signal is expected.
Four bits are provided to improve carrier detection
[CD_CD
<3..0>]. With these bits it is possible to select
a capture window (see the tables next page), and avoid a
false detection.
With the use of SCD bit the carrier detect function is
improved, because after a normal carrier detection
(NCD), a part (10 bits) of the channel seizure is taken in
count before alerting the microprocessor.
Note:
When the CPE is off hook (SCWID mode) the CO sends
FSK
data
without
channel
seizure.
The
mark signal = 80 bits
±10 at 1200 bauds (1300 Hz con-
tinuously during 67 ms).
For this case a selected bandpass 1000 Hz to 1700 Hz
could be very useful for the carrier detect ...
After the interrupt due to the carrier detect the micro-
processor can change the bandpass frequencies according
to the FSK band.
D The normal carrier detect guard time is 26.4 ms.
D The improved carrier detect guard time is 34.7 ms.
D The carrier lost guard time is 8.8 ms, in all the cases.
2.1.3
Demodulator
This part is enabled with the carrier detect signal.
The reference signal is at 1700 Hz, (the same frequency
for BELL 202 and V23). All the incoming signals are
compared to this value to make a digital square wave
frequency varying in frequency and in phase as a function
of the input frequencies.
2.1.4
Clock Recovery
The process starts at the first low-level bit received from
the demodulator. After that the CLOCK is generated for
the 10 serial bits (1 bit start, 8 bits data, 1 bit stop).When
all the data are received DATA READY is generated. This
signal loads the serial data in a parallel buffer.
DATA READY provides an indication (to the micro-
processor with an interrupt request) of the presence data
byte available.
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