MSP 34x1G
PRELIMINARY DATA SHEET
6.3. Manual/Compatibility Mode:
Individual configuration of the threshold can be done
using Table 6–5, whereby the bits 0 and 11 of
AUTO_FM are ignored. It is recommended to use the
internal setting used by the standard selection.
Description of Demodulator Write Registers
6.3.1. Automatic Switching between NICAM and
Analog Sound
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 channels.
In case of bad NICAM reception or loss of the
NICAM-carrier, the MSP 34x1G offers an Automatic
Switching (fall back) to the analog sound (FM/AM-
Mono), without the necessity of the controller 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.
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 6–5.
Note, that the channel matrix of the corresponding out-
put channels must be set according to the
NICAM mode and need not to be changed in the
FM/AM-fallback case.
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.
Example:
Required threshold = 500: bits [10:1]=00 1111 1010
6.3.1.1. Function in Automatic Sound Select Mode
Selected Sound
NICAM
The Automatic Sound Select feature (MODUS[0]=1)
includes the procedure mentioned above. By default, the
internal ERROR_RATE threshold is set to 700dec. i.e. :
– NICAM → analog Sound if ERROR_RATE > 700
– analog Sound → NICAM if ERROR_RATE < 700/2
analog
ERROR_RATE
Sound
threshold/2
threshold
The ERROR_RATE value of 700 corresponds to a
BER of approximately 5.46*10-3/s.
Fig. 6–1: Hysteresis for Automatic Switching
Table 6–5: Coding of Automatic NICAM/Analog Sound Switching; Reset Status: Mode 0
Mode
Description
AUTO_FM [11:0]
ERROR_RATE- Source Select:
Threshold/dec
Addr. = 00 21
Input at NICAM Path1)
hex
0
Compatible to MSP 3410B, i.e.
automatic switching is disabled
Bit
[0]
= 0
none
always NICAM; Mute in
case of no NICAM available
Bits [10:1] = 0
Bit
[11] = 0
[0] = 1
[10:1] = 0
[11] = 0
1
2
Automatic Switching with
internal threshold
(Default, if Automatic Sound
Bit
Bit
Bit
700
NICAM or FM/AM,
depending on
ERROR_RATE
Select is on)
Automatic Switching with
external threshold
(Customizing of Automatic
Bit
Bit
[0]
= 1
set by customer;
recommended
range: 50...2000
[10:1] = 25..1000
= threshold/2
Sound Select)
Bit
Bit
[11]
= 0
3
Forced analog mono mode, i.e.
[0]
= 1
none
always FM/AM
Automatic Switching is disabled Bit
[10:1] = 0
[11] = 1
(Customizing of Automatic
Sound Select)
Bit
1)
In case of Automatic Sound Select (MODUS[0] = 1), the NICAM path may be assigned to “Stereo or A/B”, “Stereo or A”, or
“Stereo or B” source channels (see Table 2–2 on page 12).
In case of Automatic Sound Select (MODUS[0] = 1), bit [0] of AUTO_FM is ignored
86
MICRONAS INTERMETALL