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Service Manual CP-785A
In the TDA936x series, the following geometry parameters can be adjusted for all picture tubes :
Horizontal shift
Vertical amplitude
Vertical slope
S-correction
Vertical shift
The types which are intended to be used in combination with 110° picture tubes have an East-West
control circuit. The additional controls for these types are:
EW width
EW parabola width
EW upper and lower corner parabola correction
EW trapezium correction
Vertical zoom, horizontal parallelogram and bow correction.
Chroma and luminance processing
The chroma band-pass and trap circuits (including the SECAM cloche filter) are realised by means of
gyrators and are tuned to the right frequency by comparing the tuning frequency with the reference
frequency of the colour decoder. The luminance delay line and the delay cells for the peaking circuit are
also realised with gyrators. The circuit contains a black stretcher function which corrects the black level
for incoming signals which have a difference between the black level and the blanking level.
Colour decoder
The ICs can decode PAL, NTSC and SECAM signals. The PAL/NTSC decoder does not need external
reference crystals but has an internal clock generator which is stabilised to the required frequency by
using the 12 MHz clock signal from the reference oscillator of the -Controller/Teletext decoder.
The Automatic Colour Limiting (ACL) circuit (switchable via the ACL bit in subaddress 2OH) prevents
that oversaturation occurs when signals with a high chroma-to-burst ratio are received. The ACL circuit
is designed such that it only reduces the chroma signal and not the burst signal. This has the advantage
that the colour sensitivity is not affected by this function.
SOFTWARE CONTROL
The CPU communicates with the peripheral fonctions using Special function Registers (SFRS) which are
addressed as RAM locations. The registers for the Teletext decoder appear as normal SFRs in the -
Controller memory map and are written to these functions by using a serial bus. This bus is controlled by
dedicated hardware which uses a simple handshake system for software synchronisation.
For compatibility reasons and possible re-use of software blocks, the TV processor is controlled by I2C
bus. The TV processor control registers cannot be read. Only the status registers can be read ( Read
address 8A ).
The SECAM decoder contains an auto-calibrating PLL demodulator which has two references, via the
divided 12 MHz reference frequency (obtained from the -Controller) which is used to tune the PLL to
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