9 Circuit description new circuits35L7.3A
9.6.3 Video controller (IC7225-5C, see diagram A4)YIn case of no TXT another (C is used with less pins. This
uC is indicated in the diagrams with the internal pin
The main functions are :numbering.
� Y/(B-Y)/(R-Y) signal processing/matrixIn the description below, the pin numbers are the numbers
� RGB signal selection/processing/output stagesmentioned outside the housing of IC 7600 (IC7600 with TXT
� Black stretcherand IC7601 without TXT). In case of the (C with integrated
� Beam current limiter (BCL,PWL)teletext function the CVBS-TXT signal is fed to pin 23, the TXT
� Automatic black current stabilization (ABS) .and OSD- information are combined at pins 32,33 and 34.
Y/(B-Y)/(R-Y) signal processing/matrixBefore the RGB signal selection the RGB signals are clamped
to similar DC level during burst key period. The selection is
The luminance at pin 27 is internally AC coupled to thecontrolled by the RGB insertion input voltage at pin 26.
luminance clamp, which is operational during burst key period.
The luminance signal is supplied to the RGB matrix circuit via
the black stretcher. The (B-Y)/(R-Y) signals supplied to pins 31
and 32 are clamped during the burst key period. The signalsVoltage at pin 26 selected RGB signals
are then supplied to the colour difference matrix to select the < 0.3V RGB(internal)
desired matrix formv either PAL, NTSC or Japanese NTSC
matrix. The selected matrix is controlled via the 12C bus. For
RGB matrix the signal outputs from the colour difference 0.9V < V < 3V (R_TXT G_TXT B_TXT (fast
insertion at pins 23, 24 and 25)
matrix are added with the luminance signal in colour to
generate the internal RGB signals. > 4VOSD can be inserted at the
RGB-out pins
RGB signal selection/processing/output stages
The contrast, brightness and white-point RGB adjustment on
Within the RGB signal selection there are three modes:
the selected RGB signals are controlled by 12C commands.
After the adjustment, three RGB black levels are added to the
� RGB (internal)RGB signals. These three signals are blanked when the RGB
� Fast RGB insertion (R_TXT G_TXT B_TXT on pins 23, 24blank signal is active. The RGB output stages supply the
and 25)
� OSD-modebuffered RGB signals pins 21, 20 and 19.
Black Stretcher
Teletext
Two different types of microprocessors IC7600/7601 are used:The black stretcher circuit, which is only operational during line
scan, extends the gray signal level towards the actual black
one with teletext(TXT) and one without teletext.level (= actual black level measured during burstkey). The
amount of extension is dependent on the difference between
The micro-controllers are:
actual black level and the darkest part of the incoming video
signal. The darkest part of the videosignal is registered in the
capacitor at pin 39 by means of an internal discharge current
of approximately 130uA. The black stretcher is made inactive if
P83Cx6642 pinsNormalROM size
the voltage at pin 39 is set to ground. This is done by turning on
transistor 7220, the command blackstraw coming from thevaries
microprocessor (if power button on the remote control unit is
SAA529x52 pinsControlROM size
activated).withTeletextvaries
P83CX6952 pinsControl withROM sizeBeam Current Limiter
Close captionvaries
The beam current limiter circuit functions as an average white
limiter as well as peak white limiter. The average white limiter
needs external circuitry comprising of 7265, and associated
components to function; the peak white limiter is an internal
Type ofType of tuningSystemCountries
detection circuit. The function of the beam current limitermicro-
(average white / peak white limiter) reduces the contrast andcontroller
brightness of RGB signals. For beam current limiting, the
P83Cx66VSTPAL/SECAMAPdifference in beam current (1BCL) and an internal charge
current (1CHARGE) is stored in capacitor 2460 on pin 22. If
PLLNTSCLatam1BCL > 1CHARGE voltage (VBCL) at pin 22 will decrease.
For beam current limiter contrast reduction begins if VBCL <
SAA529xVSTPAL/SECAM AP3.5V and brightness reduction begins if VBCL < 2.5V. VBCL is
normally about 4V if the beam current limiter is not active .
P83Cx169PLLBiNorma/Latam
The contrast and/or brightness reduction of the RGBout isTriNorma
proportional to the voltage decrease at pin 22.
The oscillator to be used is 12MHz; a crystal oscillator will be
used for all the micro-controllers.9.6.4 Horizontal synchronization IC 7225-5D and the line output
YIn case of TXT this function is integrated together with thestage (see diagram A3)
control part in one and the same uC. This uC is indicatedProtections:
in the diagrams with the outer pin numbering.
The line deflection incorporates protections like: |
ACEC
