STV0056AF View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'STV0056AF' PDF : 27 Pages View PDF
STV0056AF
FM DEMODULATION SOFTWARE ROUTINE (continued)
2nd STEP (LEFT) :
In practice :
VCO FREQUENCY CHECKING (VCO)
- SW3 closed ⇒ R6 B4 = H
This second step is actually a waiting loop in which - SW4 opened ⇒ R6 B2 = L
the actual running frequency of the VCO is meas-
ured.
To exit of this loop is allowed when : Subcarrier
Frequency - 10kHz ≤ Measured Frequency ≤ Sub-
carrier Frequency + 10kHz (± 10kHz is the maxi-
mum dispersion of the frequency synthesis
function).
After this sequence of 3 steps for left channel,
a similar sequence is needed for the right channel.
Note :
In the sequence for the right, there is no need to
again select the FM deviation (once is enough for
the pair).
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 depends on how large is
frequency difference between the start frequency
General Remark
Before to enable the demodulated signal to the
audio output, it is recommandedto keep the muting
and to check whether a subcarrier is present at the
wanted frequency. Such an informationis available
in R8 B0 and R8 B4 which can be read.
and the targeted frequency. Typically :
- the rate of change of the VCO frequencyis about
3.75MHz/s (Cpump = 10µF)
- In addition to this settling time, 100ms must be
added to take into account the sampling period of
the watchdog.
Two different strategies can be adoptedwhen ena-
bling the output :
- Either both left and right demodulatedsignals are
simultaneously authorized when both channel
are ready.
- Or while the right channelsequenceis running,the
already ready left signal is sent to the left and right
3rd STEP (LEFT)
outputs and the real stereo sound L/R is output
when bothchannelsare ready. This second option
TheFM demodulationcan be startedby connecting
gives sound a few hundreds of ms before the first
the VCO to the phase locked loop (PLL).
one.
24/27
Share Link: 
