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參數(shù)資料
| 型號(hào)： | STV0056AF |
| 廠商： | 意法半導(dǎo)體 |
| 英文描述： | Satellite Sound and Video Processor(衛(wèi)星探測(cè)和視頻處理器) |
| 中文描述： | 衛(wèi)星聲音和視頻處理器（衛(wèi)星探測(cè)和視頻處理器） |
| 文件頁數(shù)： | 24/27頁 |
| 文件大?。?/td> | 224K |
| 代理商： | STV0056AF |
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FMDEMODULATION SOFTWARE ROUTINE
(continued)
2
nd
STEP (LEFT) :
VCO FREQUENCY CHECKING (VCO)
Thissecondstepis actuallya waitingloop in which
the actual running frequencyof the VCO is meas-
ured.
To exit of this loop is allowed when : Subcarrier
Frequency- 10kHz
≤
MeasuredFrequency
≤
Sub-
carrier Frequency + 10kHz (
±
10kHz is the maxi-
mum dispersion of the frequency synthesis
function).
In practice, R8 B2 B3 and R9 are read and com-
pared to the value loaded in R6 B6 B7 and R7
±
1 bit.
Note :
The duration of this step dependson how large is
frequencydifference between the start frequency
and the targetedfrequency.Typically :
- therate ofchangeof theVCOfrequencyis about
3.75MHz/s(C
pump
= 10
μ
F)
- In addition to this settling time, 100ms must be
added to takeintoaccountthe samplingperiodof
the watchdog.
3
rd
STEP (LEFT)
TheFMdemodulationcanbestartedbyconnecting
the VCO to the phase lockedloop (PLL).
In practice:
- SW3 closed
R6 B4 = H
- SW4 opened
R6 B2 = L
After this sequence of 3 steps for left channel,
a similarsequenceis neededfor the rightchannel.
Note :
In the sequence for the right, there is no need to
again select the FM deviation (once is enough for
the pair).
GeneralRemark
Before to enable the demodulated signal to the
audiooutput,itisrecommandedto keepthemuting
and to checkwhethera subcarrieris presentat the
wantedfrequency.Suchan informationisavailable
in R8 B0 and R8 B4 which can be read.
Twodifferentstrategiescan beadoptedwhenena-
bling the output:
- Eitherboth leftandright demodulatedsignalsare
simultaneously authorized when both channel
are ready.
- Orwhiletherightchannelsequenceisrunning,the
alreadyreadyleftsignalis senttotheleftandright
outputs and the real stereo sound L/R is output
whenbothchannelsareready.Thissecondoption
givessound a few hundredsof ms beforethe first
one.
STV0056AF
24/27
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