MSP 34x1G
PRELIMINARY DATA SHEET
6.4.4. NICAM Error Rate Register
6.4.7. Automatic Search Function for FM-Carrier
Detection in Satellite Mode
ERROR_RATE
Error free
00 57hex
0000hex
07FFhex
The AM demodulation ability of the MSP 34x1G offers
the possibility to calculate the “field strength” of the
momentarily selected FM carrier, which can be read
out by the controller. In SAT receivers, this feature can
be used to make automatic FM carrier search possi-
ble.
maximum error rate
Average error rate of the NICAM reception in a time
interval of 182 ms, which should be close to 0. The ini-
tial and maximum value of ERROR_RATE is 2047.
This value is also active if the NICAM bit of
MODE_REG is not set. Since the value is achieved by
filtering, a certain transition time (approx. 0.5 sec) is
unavoidable. Acceptable audio may have error rates
up to a value of 700 int. Individual evaluation of this
value by the controller and an appropriate threshold
may define the fallback mode from NICAM to
FM/AM-Mono in case of poor NICAM reception.
For this, the MSP has to be switched to AM-mode
(MODE_REG[8]), FM-Prescale must be set to
7Fhex = +127dec, and the FM DC notch (see section
6.5.7.) must be switched off. The sound-IF frequency
range must now be “scanned” in the MSP-channel 2
by means of the programmable quadrature mixer with
an appropriate incremental frequency (i.e. 10 kHz).
After each incrementation, a field strength value is
available at the quasi-peak detector output (quasi-
peak detector source must be set to FM), which must
be examined for relative maxima by the controller. This
results in either continuing search or switching the
MSP back to FM demodulation mode.
The bit error rate per second (BER) can be calculated
by means of the following formula:
BER = ERROR_RATE * 12.3*10−6 /s
During the search process, the FIR2 must be loaded
with the coefficient set “AUTOSEARCH”, which
enables small bandwidth, resulting in appropriate field
strength characteristics. The absolute field strength
value (can be read out of “quasi-peak detector output
FM1”) also gives information on whether a main FM
carrier or a subcarrier was detected; and as a practical
consequence, the FM bandwidth (FIR1/2) and the
deemphasis (50 µs or adaptive) can be switched
accordingly.
6.4.5. PLL_CAPS Readback Register
It is possible to read out the actual setting of the
PLL_CAPS. In standard applications, this register is
not of interest for the customer.
PLL_CAPS
02 1Fhex L
minimum frequency
nominal frequency
1111 1111
FFhex
56hex
Due to the fact that a constant demodulation frequency
offset of a few kHz leads to a DC level in the demodu-
lated signal, further fine tuning of the found carrier can
be achieved by evaluating the “DC Level Readout
FM1”. Therefore, the FM DC Notch must be switched
on, and the demodulator part must be switched back to
FM-demodulation mode.
0101 0110
RESET
maximum frequency
PLL_CAPS
0000 0000
00hex
02 1Fhex
H
PLL open
xxxx xxx0
xxxx xxx1
For a detailed description of the automatic search
function, please refer to the corresponding MSP Win-
dows software.
PLL closed
6.4.6. AGC_GAIN Readback Register
It is possible to read out the actual setting of
AGC_GAIN in Automatic Gain Mode. In standard
applications, this register is not of interest for the cus-
tomer.
AGC_GAIN
02 1Ehex
max. amplification
(20 dB)
0001 0100
14hex
00hex
min. amplification
(3 dB)
0000 0000
94
MICRONAS INTERMETALL
MICRONAS [ MICRONAS ]
