STV0056A STMicroelectronics, STV0056A Datasheet - Page 23

• Manufacturer Part Number: STV0056A
• Description: Video ICs Analog Sound/Video
• Manufacturer: STMicroelectronics
• Type: Audio DSPr

Specifications of STV0056A

• Maximum Operating Temperature: + 70 C
• Package / Case: PDIP-56
• Minimum Operating Temperature: 0 C
• Mounting Style: Through Hole
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

FM DEMODULATION SOFTWARE ROUTINE (continued)
2
VCO FREQUENCY CHECKING (VCO)
This second step is actually a waiting loop in which
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).
In practice, R8 B2 B3 and R9 are read and com-
pared to the value loaded in R6 B6 B7 and R7
Note :
The duration of this step depends on how large is
frequency difference between the start frequency
and the targeted frequency. Typically :
- the rate of change of the VCO frequency is about
- In addition to this settling time, 100ms must be
3
The FM demodulationcan bestarted by connecting
the VCO to the phase locked loop (PLL).
nd
1 bit.
rd
3.75MHz/s (C
added to take into account the sampling period of
the watchdog.
STEP (LEFT)
STEP (LEFT) :
pump
= 10 F)
In practice :
- SW3 closed
- SW4 opened
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).
General Remark
Before to enable the demodulated signal to the
audio output, it is recommanded to keep the muting
and to check whether a subcarrier is present at the
wanted frequency. Such an information is available
in R8 B0 and R8 B4 which can be read.
Two different strategies can be adopted when ena-
bling the output :
- Either both left and right demodulated signals are
- Or while the right channel sequenceis running, the
simultaneously authorized when both channel
are ready.
already ready left signal is sent to the left and right
outputs and the real stereo sound L/R is output
when both channelsare ready. This second option
gives sound a few hundreds of ms before the first
one.
R6 B4 = H
R6 B2 = L
STV0056A
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