STV8203 ST Microelectronics, STV8203 Datasheet - Page 24

• Manufacturer Part Number: STV8203
• Description: MULTISTANDARD TV SOUND DEMODULATOR
• Manufacturer: ST Microelectronics

STV8203
PROGRAMMING THE DEVICE (continued)
CRF2 - CRF1 (FM/QPSK PLL Demodulator Offset)
Address
Type
Reset
This register provides access to the instantaneousfrequency of the PLL (2’s complement). If written to, it
will preset the DCO frequency; if read it provides the instantaneousfrequencyoffset of the PLL’s and could
be used for an AFC function.
CETH2 - CETH1 (FM Carrier Level Threshold)
Address
Type
Reset
These registers, which perform the same function in channel 1 and channel 2, compare the carrier level in
the channel against the threshold value. This level is measured after the channel filter and is relative to the
full scale reference level (0dB).
This is used as part of the validation of an FM signal, if the carrier level is below the threshold, the signal
is considered to be non-valid.
If CETH is OFF, any carrier level will be accepted.
The reset value is 53, it means a threshold of -20dB.
SQTH2- SQTH1 (FM Squelch Threshold)
Address
Type
Reset
The squelch detector measures the level of high frequencynoise (>40kHz) and comparesit to the threshold
SQTH. If the level is below this value, the S/N of the FM signal is considered to be acceptable.
Values are given for FM with 50kHz deviation :
The reset value is 60, it means a SNR of 15dB.
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bit 7
bit 7
bit 7
: 20-3D
: R/W
: 0000 0000
: 21-3E
: R/W
: 0011 0101
: 22-3F
: R/W
: 0011 1100
bit 6
bit 6
bit 6
CHANNEL 2 or CHANNEL 1 CARRIER RECOVERY FREQUENCY
SQTH
CETH
255
128
250
119
64
32
....
60
35
22
0
CHANNEL 2 or CHANNEL 1 SQUELCH-THRESHOLD
CHANNEL 2 or CHANNEL 1 CARRIER-THRESHOLD
bit 5
bit 5
bit 5
bit 4
bit 4
bit 4
bit 3
bit 3
bit 3
bit 2
bit 2
bit 2
Threshold (dB)
S/N (dB)
OFF
-12
-18
-24
....
10
15
20
25
-6
0
bit 1
bit 1
bit 1
bit 0
bit 0
bit 0