TDA9874H View Datasheet(PDF) - Philips Electronics
Part Name
Description
Manufacturer
TDA9874H Datasheet PDF : 56 Pages
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Philips Semiconductors
Digital TV sound demodulator/decoder
Preliminary specification
TDA9874H
6.1.9 NICAM AUTO-MUTE
This function is enabled by setting bit AMUTE LOW
(see Section 7.3.11). Upper and lower error limits may be
defined by writing appropriate values to two registers in the
I2C-bus section (see Sections 7.3.13 and 7.3.14). When
the number of errors in a 128 ms period exceeds the upper
error limit, the auto-mute function will switch the output
sound from NICAM to whatever sound is on the first sound
carrier (FM or AM) or to the analog mono input. When the
error count is smaller than the lower error limit, the NICAM
sound is restored.
The auto-mute function can be disabled by setting bit
AMUTE HIGH. In this case clicks become audible, when
the error count increases. The user will hear a signal of
degrading quality.
A decision to enable/disable the auto-muting is taken by
the microprocessor based on an interpretation of the
application control bits C1, C2, C3 and C4, and possibly
any additional strategy implemented by the setmaker in
the microcontroller software.
When the AM sound in NICAM L systems is demodulated
in the 1st sound IF and the audio signal connected to the
mono input of the TDA9874H, the controlling
microprocessor has to take care of switching from NICAM
reception to mono input, if auto-muting is desired. This
could be achieved by setting the AMSEL bit HIGH
additionally to AMUTE bit LOW (see also Section 7.3.11).
6.1.10 CRYSTAL OSCILLATOR
A circuit diagram of the external components of the
voltage-controlled crystal oscillator is shown in Fig.7 in
Chapter 9.
6.1.11 TEST PINS
All test pins are active HIGH. In normal operation of the
device they can be left open-circuit, as they have internal
pull-down resistors. Test functions are for manufacturing
tests only and are not available to customers.
1998 Apr 27
11
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