Technicolor - Thomson ICC19, Principles And Maintenance

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RGB SWITCHING
RGB and FB signals from SCART connector AV1 are sent to:
• The video processor, IV001, for a 50-Hz television set.
• The demodulator, IV601, for a 100-Hz television set.
DETECTING A FAST SWITCH, FB (100-Hz MODEL)
The microcontroller must be informed of the presence of a fast switch to
perform all switching of TV interfaces (RGB switching, mode display and
inlay). The fast switch can, however, be in pulse form. This is what happens
for inlays. The fast switch occurs only when characters need to be displayed
on screen. The microcontroller cannot constantly test for presence of a fast
switch; it does so periodically, at the rate allowed by its software. This is why
the appearance of a fast switch must be stored in memory. This is the
function of TV600 or TV601, whose layout is equivalent to a pseudo-thyristor.
APPLICATION:
• Pin 16 = 0 -> TV600/TV601 blocked -> input Pin 62 of Microcontroller
IR001 = 4.5 V. The microcontroller interprets this as absence of fast
switching.
• Pin 16 = 1.5 V -> TV600/TV601 saturated -> Pin 62 of microcontroller =
0.8 V. The microcontroller identifies the presence of a fast switch.
If the fast switch disappears, Pin 16 = 0. Pin 62 of the microcontroller remains
at 0.8 V, because the thyristor effect keeps TV600 and TV601 saturated.
This is a memory effect that allows the sequence to be completed.
As has already been mentioned, the microcontroller performs cyclical
resetting of Pin 62, which inhibits the thyristor effect. A few seconds after the
fast switch disappears from Pin 16, Pin 62 of the microcontroller goes to 0,
the thyristor effect disappears, 5 V at Pin 62. The microcontroller can detect
a new fast switch at Pin 16.
NOTES :
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