Philips Semiconductors
Preliminary specification
TV and VTR stereo/dual sound processor
with digital identification
TDA9847
After that, when C4 is HIGH (see Table 2), the switch
positions of the SCART channel are changed in
accordance with the other control line levels.
EXTERNAL MODE
External sound sources, e.g. from SCART input, are fed to
both AF channel pair outputs. When the user chooses the
external mode of the main channel (see Table 1), the
identification circuit is still running, but the LEDs are
switched-off.
When the supply voltage of the TDA9847 is not connected
(standby function), the control lines remain undisturbed.
The logic level combination 1000 of the control input ports
(C4, C3, C2 and C1) is not allowed (see Tables 1 and 2).
Programming of the main and SCART register
Operating mode selection
GENERAL INFORMATION
Tables 1 and 2 show the different operating modes of this
stereo decoder.
The switch positions of both AF channels are directly
controlled by the data of the main and SCART register.
These registers are programmable by a microcontroller.
MUTE MODE
In the 3-state mode the logic content of the C1, C2 and C3
control lines remains stored in the registers for main and
SCART, so the switch positions in the source selector do
not change. The logic content of these control lines can be
changed without changing the switch positions of the
source selector (preset position) to prepare the new
operating mode selection for the main or SCART channel.
The execution of this new mode is achieved by leaving the
preset position (3-state): When the C4 level goes LOW,
the logic content of the control lines C1, C2 and C3 are
valid for the main channel (see Table 1) and in the event
of HIGH the C1, C2 and C3 are valid for the SCART
channel (see Table 2).
This IC has two different mute modes:
1. Mute mode.
2. Sound mute mode.
In the mute mode, when all control input lines are set LOW,
all AF channels are muted (‘fast mute’). Finally, the
integrators are reset provided the user does not leave this
mode (identification is disabled). When the user changes
this mode, the identification circuit starts with the
detection.
In the sound mute mode each AF channel can be
separately muted (0100 = main and 1100 = SCART). The
identification circuit is activated and the LEDs are on or off
in accordance with the detection status of this circuit.
The identification bits and the control lines influence the
operating mode selection for the AF switches in the source
selector and de-matrix, e.g. both AF channels are
programmed in the mono mode (X001,
MONO MODE
see Tables 1 and 2). The LEDs are switched-off. When
the identification circuit detects the stereo identification
frequency (fs = 117 Hz) the de-matrix is immediately
switched in the stereo mode without changing the control
line levels. The stereo signals are routed to all AF outputs.
In the event of dual frequency detection (fD = 274 Hz) both
dual sounds are fed to the AF output pairs.
For the transmitter status mono the user must set the
TDA9847 in the mono mode with X001 or X010
(see Tables 1 and 2). The level combination X011 is
reserved for the AM sound (standard L), because in this
mode the de-emphasis is deactivated and the gain of the
AF signal from input to output is reduced from
6 dB to 0 dB. At the AF outputs the signal has the same
level for standards with FM or AM modulated sound
assuming the same modulation degree.
MICROCONTROLLER WITH 3-STATE OUTPUT PORTS
Figure 10 shows an example of an application circuit for
TDA9847 (VP = 4.5 to 8.8 V) in conjunction with a
microcontroller, which has a LOW/high-ohmic/HIGH
output port to control the main and SCART channel (C4
control line). For the C1, C2 and C3 line the microcontroller
requires only LOW/HIGH output ports. Two resistors RC4A
and RC4B are necessary for the C4 line to generate the
3-state voltage. The values and tolerances of these
components are given in Fig.10.
STEREO MODE
In this mode the choice between stereo and mono (‘forced
mono’) signals is common for both AF channel pairs. The
mode for main and SCART is achieved by control of the
main channel (see Tables 1 and 2).
DUAL MODE
In this mode there is no restriction to select AF inputs and
outputs independently in both channels.
1995 May 23
7
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