Daewoo DUB-2850GB Service Manual page 47

signals and nominal settings of the various controls.
To obtain an accurate biasing of the picture tube the Continuous Cathode Calibration system
has been included in these ICs. The system is slightly adapted compared with the previous
circuits. In the new configuration the cut-off level of the picture tube is controlled with a
continuous loop whereas the correction of the amplitude of the output signals is realised by
means of a digital loop. As a consequence the current measurement can be controlled from
the-Processor. The value of the highcurrent intheCCCloopcanbechosenviatheSLG0 and SLG1
bits (subaddresses 42H and 46H). The gain control in the 3 RGB channels is realised by means
of 7-bit DACs. The total gain control range is6 dB. The change in amplitude at the cathodes of
the picture tube for one LSB is about 1.1 Vp-p. The setting of the control DAC is determined by
the following registers:
* The white point setting of the R, G and B channel in subaddress 20H to 22H. This register has
a resolution of 6 bits and the control range in output signal amplitude is +/-3 dB.
* The cathode drive setting (CL3-CL0 in subaddress 42H). This setting is valid for all channels,
there solution is 4 bits and the control range is +/-3 dB.
* The gain setting of the R, G and B channel. During switch on this register is loaded with the
preset gain setting of subaddress 23H to 25H and when necessary it will be adapted by the
CCC control loop. These registers have a resolution of 7 bits. The control of the gain setting is
illustrated in table below.
WPR(GB) 0
CL 0
CCC-gain B6
R(GB)-gain B6
The setting of the gain registers of the 3 channels can be stored during switch off and can be
loaded again during switch-on so that the drive conditions are maintained.
When required the operation of the CCC system can be changed into a one-point black current
system. The switching between the 2 possibilities is realised by means of the EGL bit (EGL = 0)
in subaddress 42H. When used asone-point control loop the system will control the black level
of the RGB output signals to the low reference current and not on the cut off point of the
cathode. In this way spreads in the picture tube characteristics will not be taken into account. In
this condition the settings of the white point control registers (subaddress 20H-22H) and the
cathode drive level bits (CL3 - CL0 in subaddress 42H) are added to the settings of the RGB
preset gain registers (subaddress 23H - 25H).
A black level off-set can be made with respect to the level which is generated by the black
current stabilization system. In this way different colour temperatures can be obtained for the
bright and the dark part of the picture. The black level control is active on the Red and the
Green output signal. It is also possible to control the black level of the Blue and the Green
output signal (OFB bit = 1).
In the Vg2 adjustment mode (AVG=1) the black current stabilization system checks the output
level of the 3 channels and indicates whether the black level of the highest output is in a certain
B5 B4 B3
B3 B2 B1
B5 B4 B3
B5 B4 B3
B2 B1
B0 0
B2 B1
B2 B1
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CP-780 Service Manual
B0 Max 64
0 Max 60
B0 Max 126
B0 Max 126