STV0042A/Z STMicroelectronics, STV0042A/Z Datasheet - Page 26

• Manufacturer Part Number: STV0042A/Z
• Description: Video ICs Analog Sound/Video
• Manufacturer: STMicroelectronics
• Type: Audio DSPr

Specifications of STV0042A/Z

• Maximum Operating Temperature: + 70 C
• Package / Case: PDIP-42
• Minimum Operating Temperature: 0 C
• Mounting Style: Through Hole
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

FM Demodulation Software Routine
6.1.2
6.1.3
Note: 1 The FM deviation does not have to be selected again for the right channel (once is enough for the
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2 Before sending the demodulated signal to the audio output, it is recommended to keep the muting
Table 5
2nd Step (Left): VCO Frequency Checking (VCO)
This second step is actually a waiting loop in which the actual running frequency of the VCO is
measured.
This loop can be exited when:
Where, ±10 kHz is the maximum dispersion of the frequency synthesis function).
In practice, R8 B[3:2] and R9 B[7:0] are read and compared to the value loaded in R6 B[7:6] and R7
B[7:0] ±1 bit.
The duration of this step depends on the difference between the start frequency and the targeted
frequency. Typically:
3rd Step (Left)
The FM demodulation can be started by connecting the VCO to the phase locked loop (PLL).
In practice:
After this sequence of 3 steps for left channel, a similar sequence is required for the right channel.
pair).
and to check whether a subcarrier is present at the desired frequency. Such information can be read
in R8 B0 and R8 B4.
Two different strategies can be adopted when enabling the output:
2.2 Load R7 B[7:0] and R6 B[7:6] with the values corresponding to the left channel frequency.
(10 kHz is the minimum step of the frequency synthesis function). Since the tuning range is
between 5 and 10 MHz, the coded value is a number between 500 and 1000 (210 = 1024).
This value is coded on 10 bits.
Example:
7.02 MHz = 702 x 10 kHz
702
R7 is loaded with AF and R6 B6: 0, R6 B7: 1.
The rate of change of the VCO frequency is about 3.75 MHz/s (pin CPUMP = 10 µF)
In addition to this settling time, 100 ms must be added to take into account the sampling period
of the watchdog.
Switch K3 closed
Switch K4 open
Either both left and right demodulated signals are simultaneously authorized when both
channels are ready.
Or while the right channel sequence is running, the already ready left signal is sent to the left
and right outputs and the real stereo sound L/R is output when both channels are ready. This
second option outputs the sound a few hundred milliseconds before the first one.
Subcarrier Frequency - 10 kHz
gives the settings for the most common subcarrier frequencies.
This 10 bits value is calculated as follows:
1010 1111 10
R6 B4 = 1
R6 B2 = 0
AF + 10
Subcarrier frequency = coded value x 10 kHz
Measured Frequency
Subcarrier Frequency +10 kHz
STV0042A/Z