LM1247 National Semiconductor, LM1247 Datasheet - Page 6

• Manufacturer Part Number: LM1247
• Description: 150 MHz I2C Compatible RGB Preamplifier with Internal 512 Character OSD ROM, 512 Character RAM and 4 DACs
• Manufacturer: National Semiconductor

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LM1253A and LM1237 Compatibility
In order to maintain register compatibility with the LM1253A
and LM1237 preamplifier datasheet assignments for bias
and brightness, the color assignments are recommended as
OSD vs Video Intensity
The OSD amplitude has been increased over the LM1237
level. During monitor alignment, the three gain registers are
used to achieve the desired front of screen color balance.
This also causes the OSD channels to be adjusted accord-
ingly, since these are inserted into the video channels prior
to the gain attenuators. This provides the means to fine tune
the intensity of the OSD relative to the video as follows. If a
typical starting point for the alignment is to have the gains at
maximum (0x7F) and the contrast at 0x55, the resultant
OSD intensity will be higher than if the starting point is with
the gains at 0x55 and the contrast at maximum (0x7F). This
tradeoff allows fine tuning the final OSD intensity relative to
the video. In addition, the OSD contrast register, 0x8438
[4:3], provides 4 major increments of intensity. Together,
these allow setting the OSD intensity to the most pleasing
level.
LM1247 Pin:
Assignment:
TABLE 2. LM1253A/LM1237 Compatibility
DAC 1
Blue
DAC Bias Outputs
DAC 2
Green
6
shown in Table 2. If datasheet compatibility is not required,
then the DAC assignments can be arbitrary.
ESD Protection
The LM1247 features a 3.0 KV ESD protection level (see
(Notes 4, 13)). This is provided by special internal circuitry
which activates when the voltage at any pin goes beyond the
supply rails by a preset amount. At that time the protection is
applied to all pins, including SDA and SCL. If any signal
other than these two is applied to the LM1247 while the V
is near zero, such as horizontal and vertical deflection pulses
of sufficient amplitude, this protection will activate and pre-
vent any communication on the I
LM1247, until the other signal or signals are removed. Nor-
mally, with all other pins unenergized, the LM1247 will not
affect I
2
DAC 3
C communication when it is powered down.
Red
Brightness
DAC 4
2
C bus common to the
CC