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The picture tube measurement returns results on
every field for:
- cutoff R
- cutoff G
- cutoff B
- white drive R or G or B (sequentially)
The average beam current limiter (BCL) works on both the digital YC r C b input from VSP and the inserted analog
RGB signals (OSD and Teletext) by using the sense input for the beam current measurement. The BCL uses a different
filter to average the beam current during the active picture resulting in a 12-bit resolution. The filter bandwidth is
approximately 4 kHz. The beam current limiter allows the setting of a threshold current, a gain and an additional time
constant. To accommodate several CRT's, beam current threshold and gain can be modified by microcontroller option2.
If the beam current is above the threshold, the excess current is low-pass filtered with the according gain and time
constant. The result is used to attenuate the RGB outputs by adjusting the white drive multipliers for the internal (digital)
RGB signals, and the analog contrast multipliers for the analog RGB inputs, respectively. The lower limit of the
attenuator is programmable, thus a minimum contrast can always be set. If the minimum contrast is reached, the
brightness will be decreased to a programmable minimum as well.
5.3.2.13 Synchronization and Deflection
The deflection processing generates the signals for the horizontal and vertical drive. This block contains two numeric
phase-locked loops and a security unit:
- PLL2 generates the horizontal and vertical timing, e.g. blanking, clamping and sync signals.
Phase and frequency are synchronised by the incoming sync signals.
- PLL3 adjusts the phase of the horizontal drive pulse and compensates for the delay of the horizontal output stage.
- The security unit observes the H-Drive output signal.
With an external 5 MHz reference clock this unit controls the H-drive "off time" and period. In case of an incorrect H-
drive signal the security unit generates a free running h-drive signal divided down from beam current
5.3.2.14 EHT Compensation
The vertical deflection waveform is scaled according the average beam current. This is used to compensate the effects
of electric high tension changes due to beam current variations. EHT compensation for East/West deflection is done
with an offset corresponding to the average beam current.
5.4 MICROCONTROLLER
5.4.1 MICROCONTROLLER FEATURES
8-bit 8051 instruction set compatible CPU
33.33-MHz internal clock (max.)
0.360 s (min.) instruction cycle
Two 16-bit timers : schedule software tasks , and user clock
Watchdog timer
Capture compare timer for infrared remote control decoding
Pulse width modulation unit (2 channels 14 bit, 6 channels 8 bit) : used to control AGC Take Over Point .
ADC (4 channels, 8 bit) : AFT, AGC, Local keys, OCP.
UART
CP-850/F Service Manual
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