STV0056 데이터 시트보기 (PDF) - STMicroelectronics
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STV0056 Datasheet PDF : 37 Pages
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STV0042/STV0056 APPLICATION NOTE
3 - APPLICATION NOTES (continued)
Figure 12 : FM Demodulation Software routine Flow Chart
Start
Relevant STV42/56
(W : Write, R : Read)
Mute Audio Output
W Reg 00
1st Step
Select FM Deviation
B
Lauch Frequency Synthesis (left)
Watchdog (left)
W Reg 05 B0-5
W Reg 07
W Reg 06 B2 B4 + Reg 06 B6-7
R
Reg 09 + Reg 08 B2-3
2nd Step
Note 3
fsb - 20kHz < fVCO
< fsb + 20kHz
No
3rd Step
Yes
Demodulation Start
(PLL connected to AGC stage)
Lauch Frequency Synthesis (Right)
Wait for tAL ≈ 100ms Note 1
Left
Subcarrier
Presence
Note 4 C
Yes
No
A Note 2
R
Reg 06 B2 B4
R
Reg 07 + Reg 03 B3 B5 + Reg 06 B6-7
R
Reg 08 B0
Watchdog (right)
R
Reg 0A + Reg 08 B6-7
Note 3
fsb - 20kHz < fVCO
< fsb + 20kHz
No
Yes
Demodulation Start
(PLL connected to AGC stage)
Wait for tAL ≈ 100ms Note 1
W Reg 06 B3 B5
Right
Subcarrier
Presence
Yes
Note 4 E
Stop Muting
No
D Note 2
R
Reg 08 B4
W Reg 00
End
Notes : 1. tAL must be longer than the setting time of the voltage at AMPLOCK Pins. tAL can be reduced by decreasing the AMPLOCK capacitor.
2. In points A and D different strategies may be adopted (up to the software engineer).
Suggestion : to return to B point and to have a second trial. If this second trial is not successfull, to run till end ; in this case a randoom
noise is output and the end user is warned about the subcarrier ”abscence”.
3. The frequency synthesis has a ± 10kHz accuracy. But in order to give some more margin ± 20kHz tolerance may be used (this
tolerance remains lower than the capture range of the PLL).
4. In point C, two different strategies may be adapted :
- either to keep muted the output till the MCU runs till E point,
- or to output the left sound on both outputs untill the MCU runs to E point, and real stereo sound is output after E point.
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