MSP3450G datasheet(89/106 Pages) MICRONAS

89 / 106 page

DATA SHEET

MSP 34x0G

Micronas

May 27, 2003; 6251-476-1DS

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 34x0G 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]

(Address: 0023hex) 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 700dec. 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

set

according

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

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 21hex

ERROR_RATE-

Threshold/dec

Source Select:

Input at NICAM Path1)

Default

Automatic Switching with

internal threshold

bit[11:0] = 0

700

NICAM or FM/AM,

depending on

ERROR_RATE

Automatic Switching with

external threshold

(Customizing of Automatic

Sound Select)

bit[11]

= 0

bit[10:1] = 25...1000

= threshold/2

bit[0]

= 1

set by customer;

recommended

range: 50...2000

Forced Analog Mono

bit[11]

= 1

bit[10:1] = ignored

bit[0]

= 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 2–2 on page 12).

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