LM1246
150 MHz I2C Compatible RGB Preamplifier with Internal
512 Character OSD ROM, 512 Character RAM and 4
DACs
General Description
The LM1246 pre-amp is an integrated CMOS CRT preamp.
It has an I2C compatible interface which allows control of all
the parameters necessary to directly setup and adjust the
gain and contrast in the CRT display. Brightness and bias
can be controlled through the DAC outputs, which are well
matched to the LM2479 and LM2480 integrated bias clamp
ICs. The LM1246 preamp is also designed to be compatible
with the LM246x high gain driver family.
Black level clamping of the video signal is carried out directly
on the AC coupled input signal into the high impedance
preamplifier input, thus eliminating the need for additional
clamp capacitors. Horizontal and vertical blanking of the
outputs is provided. Vertical blanking is optional and its
duration is register programmable.
The IC is packaged in an industry standard 24-lead DIP
molded plastic package.
Features
n Fully addressable 512 Character OSD, simiilar in
features to the LM1237/LM1247, with selectable 2
byte character addressing or LM1247 bank select
modes
n Internal 512 character OSD ROM usable as either (a)
384 2-color plus 128 4-color characters, (b) 640 2-color
characters, or (c) some combination in between
n Internal 512 character RAM, which can be displayed as
one single or two independent windows
n Enhanced I2C compatible microcontroller interface
to allow versatile Page RAM access
n OSD Window Fade In/Fade Out
n OSD Half Tone Transparency
n Video Data dectection for Auto Centering & Sizing
n OSD override allows OSD messages to override video
and the use of burn-in screens with no video output.
n 4 DAC outputs (8-bit resolution) for bus controlled CRT
bias and brightness
n Spot killer which blanks the video outputs when VCC
falls below the specified threshold
n Suitable for use with discrete or integrated clamp, with
software configurable brightness mixer
n 4-Bit Programmable start position for internal
Horizontal Blanking
n Horizontal blanking and OSD synchronization directly
from deflection signals. The blanking can be disabled, if
desired.
n Vertical blanking and OSD synchronization directly from
deflection signals. The blanking width is register
programmable and can be disabled, if desired.
n Power Saving Mode with 65% power reduction
n Matched to LM246x driver and LM2479/80 bias IC’s
Applications
n Low end 15" and 17" bus controlled monitors with OSD
n 1024x768 displays up to 85 Hz requiring OSD capability
n Very low cost systems with LM246x driver