Grid For Deflection; Video Dac Data Generation - Polaroid 8035 Repair Manual

8K Series ProPalette Repair Manual
For a slow scan exposure, the three DACs for deflection and video are updated to scan
4
the beam. The Cos and Dynamic Focus DACs are updated at a slower rate.
The design goal is to be able to expose an image on 35mm film in less than 1 minute. The
exposure process includes some startup time where a brightness auto-calibration is
performed, and the exposure of three color planes; red, green, and blue. Between the
exposure of each color, the color wheel must be moved.
The time to expose a line includes the time required to sweep the crt beam horizontally,
displaying all of the pixels, and the time to retrace the crt beam to the beginning of the
next line.
The mix of activities performed by the DSP, and dedicated hardware have been chosen to
accommodate the major activities of:
• Generation of deflection values for the X and Y deflection DACs
• Generation of Cos
• Generation of video DAC values at the pixel rate.

Grid for Deflection

Digital grid point information representing horizontal, vertical, video, COS
dynamic focus data is sent to the DSP which operates on the information and controls the
output timing of this data to the analog board.

Video DAC Data Generation

Pixel data is provided from the host computer as either RGB data or in a RLE format.
RLE data is converted to raw RGB pixels. RGB data is a byte per pixel per primary color.
For each primary color, we have a byte value which indicates the density of that primary
color for each pixel.
This pixel data must be converted to video DAC data. This is a non-linear conversion
which must accommodate both the contrast of the CRT and the non-linearity of the film.
There is a non-linear one-to-one correspondence between the pixel value and the video
value. Throughout this documentation we make a distinction between pixel data and
video data. Pixel data is a byte value which represents the brightness of a pixel. Video
data is a 16 bit value to the video DAC to get that brightness on film.
Hardware is dedicated to do a pixel-to-video conversion at the required throughput rate.
The hardware is a 256 word memory which is loaded with a video lookup table. The
memory is addressed with the pixel value and the output is the video value. A DMA
channel is dedicated to sending the pixel data from it's memory to the lookup table and
the output of the lookup table is sent to the video DAC.
4
and Dynamic Focus values
69
Theory of Operation
4
, and