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DRX-1
4. Analog Board Nafta version
4.1 Microprocessor TMP93C071F
The microcontroller „AIO" TMP93C071F is a 16bit
microcontroller with internal ROM and 8kB RAM. It
includes the following functions:
• A/D converters
• composite sync input
• I
2
C bus interface
The following connection to the mains, a positive pulse on
the reset input on the P is generated by the reset-IC
TL7705 (Pos.7900).
The system clock is generated with the 20MHz quartz
(Pos. 1994).
4.2 Bus Systems
The communication between the P and the other
functional groups is via the I
rate is approx. 95kHz.
Functional groups on the I
2
• E
PROM ST24E16 (Pos. 7815)
• Tuner (Pos. 1705)
• Matrix-switch STV6410 (Pos. 7507)
• Audio IC / MSP (Pos. 7600)
• Display board (Pos. 1987)
4.3 E
2
PROM
The E
2
PROM ST24E16 (Pos. 7815) is an electric erasable
and writeable, non-volatile memory. The E
data specific to the device, such as the AFC-reference
value, clock-correction- factor, etc. The data is accessed
2
by the P via the I
C-bus.
4.4 FOME
The FOME (Follow Me) -circuit compares the video signal
coming from the tuner and the one coming from the Scart-
plug 1. If the video-signals are identical the output of the
FOME-circuit is low.
4.5 Fan Control
The fan control circuit is necessary to control the speed of
the cabinet fan (Pos. 1984) according to the requirements
in temperature and noise. The temperature is measured
via an NTC on the display board (Pos. 3145). When the
temperature is lower than 25° C the fan-voltage is approx.
5V and will reach approx. 10V at a temperature of 40° C. It
is also possible to switch off the fan via the control line
ION_FAN. The circuit generates also two control-signals:
TEMP goes to the P and BE_FAN is the control-line for the
basic engine fan.
4.6 Power Supply
The 5SW and 8SW supply are switched off in case of Stby
from the P via the ISTBY-line. This is possible for power-
save. The ISTBY-line must be low in case of STBY. There
is also a „power fail" circuit on the PS-schematic which is
necessary to mute AUDIO when IPFAIL is low.
80
2
C-bus (SDA, SCL). The clock
2
C bus:
2
PROM stores
4.7 Front End (TU, AP Part)
The front end comprises the following parts:
• Tuner [1705]
• IF amplifier & video demodulator IC TDA 9817 [7703]
• Sound processor MSP3445G [7600]
IF Selection
The IF frequency of the video carrier is 45.75 MHz. A
quasi-split audio system is used. Separate surface-wave
filters (SAW) are required. [1701] for video, [1702] for
audio.
IF Demodulator
TDA 9817
The IF signal from the tuner is processed by the
demodulator IC TDA 9817 [7703]. A QSS-audio-IF signal
SIF1 is generated for demodulation in the sound
processor [7600]. Audio carriers are converted from the
tuner IF level into the audio IF position and further
processed in the audio demodulator [7600]. The AFC coil
[5703] on the TDA 9817 is adjusted so that when a
frequency of 45.75 MHz is supplied to the IF output of the
tuner, the AFC voltage on pin 17 of the TDA 9817 is 2.5V.
The HF-AGC is set using the AGC controller [3707] so
that, with a sufficiently large antenna input signal (74 dBV)
the voltage at the IF output of the tuner [1705] pin 11 is 500
mVpp. This setting must be carried out, when the audio
carrier is switched off. The demodulated video signal
appears on pin 16 [7703].
The demodulator AGC voltage at pin4 is used to
determine the antenna signal strength after a buffer [7705]
with the signal AGC_MUTE. In the opposite direction this
line may be used to mute the demodulator to avoid
crosstalk in all cases, where the tuner signal is not
needed. In this case a „high" signal is sent via AGC_MUTE
and the conducting diode [6703] to pin4. The video trap
[1703] reduces adjacent channel video and sound carrier
remainders in the video. The demodulated video signal
VFV is available after the buffer and limiter stage for noise
peaks [7706]. The FM-PLL demodulator function of TDA
9817 is not used and deactivated by the resistor [3726].
Audio Demodulator
Sound processor MSP 3445G
The MSP 3445G [7600] is a NTSC sound processor.
Amplitude and bandwidth of the demodulated audio
signals can be determined in the MSP using the
corresponding commands via the I2C bus. The audio
signal from the tuner is available at the pins 30 AFER and
31 AFEL.
4.8 Video-Routing (Nafta Version)
General Description:
The complete Video- I/O-switching is basically realised by
the I/O switch STV6410A, which is controlled via IIC-Bus-
0 (SDA/SCL) by the all in one C on the analogue board.
The STV 6410 has three YCVBS, three chroma, and one
RGB switch which is not used in the Nafta I/O. All switches
have 6-dB amplification on the outputs. The YCVBS inputs
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