VDP 31xxB
PRELIMINARY DATA SHEET
2.11.3. Vertical and East/West Deflection
2.11.4. Protection Circuitry
– Picture tube and drive stage protection is provided
through the following measures:
The calculations of the vertical and East/West deflection
waveforms is done by the internal Fast Processor (FP).
The algorithm uses a chain of accumulators to generate
the required polynomial waveforms. To produce the
deflectionwaveforms, theaccumulatorsareinitializedat
thebeginningofeachfield. Theinitializationvaluesmust
becomputedbytheTVcontrolprocessorandarewritten
to the front-end once. The waveforms are described as
polynomials in x, where x varies from 0 to 1 for one field.
– Vertical flyback protection input: this pin searches for
a negative edge in every field, otherwise the RGB
drive signals are blanked.
– Drive shutoff during flyback: this feature can be se-
lected by software.
– Safety input pin: this input has two thresholds. Be-
tween zero and the lower threshold, normal function-
ing takes place. Between the lower and the higher
threshold, the RGB signals are blanked. Above the
higher threshold, the RGB signals are blanked and the
horizontal drive is shut off. Both thresholds have a
small hysteresis.
2
3
4
P: a + b(x–0.5) + c(x–0.5) + d(x–0.5) + e(x–0.5)
The initialization values for the accumulators a0..a3 for
vertical deflection and a0..a4 for East/West deflection
are 12-bit values.
The vertical waveform can be scaled according the
average beam current. This is used to compensate the
effects of electric high tension changes due to beam cur-
rent variations. In order to get a faster vertical retrace
timing, the output impedance of the vertical
D/A-converter can be reduced by 50% during the re-
trace.
– The main oscillator and the horizontal drive circuitry
are run from a separate (standby) power supply and
are already active while the TV set is powering up.
Fig. 2–30 shows several vertical and East/West deflec-
tion waveforms. The polynomial coefficients are also
stated.
Vertical:
a,b,c,d
0,1,0,0
0,1,1,0
0,1,0,1
East/West:
a,b,c,d,e
0,0,1,0,0
0,0,0,0,1
0,0,1,1,1
Fig. 2–30: Vertical and East/West deflection waveforms
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Micronas
MICRONAS [ MICRONAS ]
