LM1236 National Semiconductor Corporation, LM1236 Datasheet - Page 7

• Manufacturer Part Number: LM1236
• Description: 150 Mhz I2c Compatible Rgb Preamplifier With Internal 254 Character Osd Rom, 512 Character Ram And 4 Dacs
• Manufacturer: National Semiconductor Corporation

Compatibility with LM1237 and LM1247
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
LM1236 Pin:
Assignment:
TABLE 2. LM1253A/LM1237 Compatibility
DAC 1
Blue
DAC Bias Outputs
DAC 2
Green
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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.
ESD Protection
The LM1236 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 the pins, including SDA and SCL.
(Continued)
DAC 3
Red
Brightness
DAC 4
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