THOMSON VK231PS, Technical Manual

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ON-SCREEN DISPLAY (OSD)
The servo control microcontroller provides the on-screen display. It is controlled via the
STATUS key on the remote control unit.
There are two possible display modes:
- FULL SCREEN Mode,
- MIX SCREEN Mode (OSD + video composite).
The servo control microcontroller receives the HD horizontal synchronisation signal from Pin 9
of IV500 on Pin 69, and the composite synchronisation signal on Pin 70. 17.73-MHz oscillator
QT001 (i.e. 4 x 4.43 MHz) supplies the clock to Pins 79 and 78 of IT001.
FULL SCREEN MODE
Servo control microcontroller IT001 supplies a signal of amplitude 1 Vpp from its Output 75.
This signal consists of a blue backdrop (on the 4.43-MHz PAL carrier), white characters, and
the L +T synchronisation signal.
This signal is sent to switching circuit IV401 via TV401. It enters at 3 of this circuit, and leaves
via Pin 4. It is then applied to switching circuit IX004 (Pin 3), and then to the modulator.
MIX SCREEN MODE
Servo control microcontroller IT001 supplies a signal of amplitude 1 Vpp from its Output 75.
This signal consists of white characters and the L +T synchronisation signal.
From its Output 67, it supplies a fast switching signal PH1. When applied to IV401 Pin 9, this
signal inlays characters on the video.
The video signal arrives at IV401 Pin 5.