MSP3438G Datasheet, PDF (74/84 Pages) Micronas – Multistandard Sound Processor Family

MSP 3438G
PRELIMINARY DATA SHEET
6.3. Manual 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 34x8G 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.
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.
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, whereby the bits [0] and [11] of
AUTO_FM are ignored. It is recommended to use the
internal setting used by the standard selection.
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.
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.
Example:
Required threshold = 500: bits [10..1]=00 1111 1010
Selected Sound
NICAM
analog
Sound
threshold/2
threshold
ERROR_RATE
Fig. 6–1: Hysteresis for automatic switching
Table 6–5: Coding of Automatic NICAM/Analog Sound Switching; Reset Status: Mode 0
Mode
0
Description
Forced NICAM
(Automatic Switching disabled)
AUTO_FM [11..0]
Addr. = 00 21_hex
Bit [0] = 0
Bits [10..1] = 0
Bit [11] = 0
ERROR_RATE- Source Select:
Threshold/dec Input at NICAM Path¹⁾
none
always NICAM; Mute in
case of no NICAM available
1
Automatic Switching with
Bit [0] = 1
internal threshold
Bit [10..1] = 0
(Default, if Automatic Sound
Bit [11] = 0
Select is on)
700
NICAM or FM/AM,
depending on
ERROR_RATE
2
Automatic Switching with
Bit [0] = 1
set by customer;
external threshold
Bit [10..1] = 25..1000
recommended
(Customizing of Automatic
= threshold/2
range: 50...2000
Sound Select)
Bit [11] = 0
3
Forced Analog Mono
Bit [0] = 1
(Automatic Switching disabled) Bit [10..1] = 0
Bit [11] = 1
none
always FM/AM
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 11).
In case of Automatic Sound Select (MODUS[0] = 1), bit [0] of AUTO_FM is ignored
74
MICRONAS INTERMETALL