PRELIMINARY DATA SHEET
MSP 34x5G
Micronas
79
6.3. Manual/Compatibility Mode:
Description of Demodulator Write Registers
6.3.1. Automatic Switching between NICAM and
Analog Sound
In case of bad NICAM reception or loss of the
NICAM-carrier, the MSP 34x5G offers an Automatic
Switching (fall back) to the analog sound (FM/AM-
mono), without the necessity for the controller of reading
and evaluating any parameters. If a proper NICAM sig-
nal returns, switching back to this source is performed
automatically as well. The feature evaluates the NICAM
ERROR_RATE and switches, if necessary, all output
channels which are assigned to the NICAM-source, to
the analog source, and vice versa.
An appropriate hysteresis algorithm avoids oscillating
effects (see Fig. 6
–
1). STATUS[9] and C_AD_BITS[11]
(Addr: 0023 hex) provide information about the actual
NICAM-FM/AM-status.
Fig. 6
–
1:
Hysteresis for Automatic Switching
6.3.1.1. Function in Automatic Sound Select Mode
The Automatic Sound Select feature (MODUS[0]=1)
includes the procedure mentioned above. By default, the
internal ERROR_RATE threshold is set to 700
dec
. i.e.:
–
NICAM
→
analog Sound if ERROR_RATE
>
700
–
analog Sound
→
NICAM if ERROR_RATE
<
700/2
The ERROR_RATE value of 700 corresponds to a
BER of approximately 5.46*10
-3
/s.
Individual configuration of the threshold can be done
using Table 6
–
5. However, the internal setting used by
the standard selection is recommended.
The optimum NICAM sound can be assigned to the
MSP output channels by selecting one of the
“
Stereo
or A/B
”
,
“
Stereo or A
”
, or
“
Stereo or B
”
source chan-
nels
6.3.1.2. Function in Manual Mode
If the manual mode (MODUS[0]=0) is required, the
activation and configuration of the Automatic Switching
feature has to be done as described in Table 6
–
6.
Note, that the channel matrix of the corresponding out-
put-channels
must
be
NICAM-mode and need not to be changed in the FM/
AM-fallback case.
set
according
to
the
Example:
Required threshold = 500: bits[10:1] = 00 1111 1010
ERROR_RATE
Selected Sound
NICAM
analog
sound
threshold
threshold/2
Table 6
–
5:
Coding of Automatic NICAM/Analog Sound Switching;
Automatic Sound Select is on (MODUS[0] = 1)
Mode
Description
AUTO_FM [11:0]
Addr. = 00 21
hex
ERROR_RATE-
Threshold/dec
Source Select:
Input at NICAM Path
1)
1
Default
Automatic Switching with
internal
threshold
bit[11:0] = 0
700
NICAM or FM/AM,
depending on
ERROR_RATE
2
Automatic Switching with
external
threshold
(Customizing of Automatic
Sound Select)
bit[11]
bit[10:1] = 25...1000
= threshold/2
bit[0]
= 1
= 0
set by customer;
recommended
range: 50...2000
3
Forced Analog Mono
bit[11]
bit[10:1] = ignored
bit[0]
= 1
= 1
always FM/AM
1)
The NICAM path may be assigned to
“
Stereo or A/B
”
,
“
Stereo or A
”
, or
“
Stereo or B
”
source channels
(see Table 2
–
1 on page 11).