Service manual

ADC/DAC
Analogue to Digital conversion is done with three identical 9-bit ADC's.
Digital to Analogue conversion uses three identical 10-bit DACs.
In the PICNIC there are three 9 bits ADCs present for Y, U and V. For digitizing the Y
(luminance) 9 bits are used, to realize a more detailed picture. The nine bits are only
used internally. Via dithering, the nine bits are reduced to eight bits and that data is
stored in memory. The data in memory is fed back to the PICNIC and via un-dithering
the data is again reproduced in nine bits for processing.
U/V (color difference signals) is also sampled with nine bits. These two nine bit data
streams are multiplexed to four bit data streams. This reduction can be allowed, as the
perception for colors by the human eye is less sensitive as for luminance.
Interlaced to Progressive Scan Conversion
The main task of the PICNIC is the conversion from interlaced 60 Hz to progressive
scan 60 Hz for YUV and HV-sync. In order to remove 'large area flicker' (especially
visible in a white picture), the field-rate of the video is doubled by the FBX6. The line
frequency (16 kHz) is doubled (32 kHz). When the video input contains fields A, B etc,
the conversion provides an AABB sequence on the display. The actual conversion is
done in the first Field Memory by reading it twice at double speed, while writing it once.
Automatic Aspect Ratio Adaptation (AARA)
This feature uses data from the 'black bar detection circuit' to adapt the vertical and
horizontal amplitude to an aspect ratio belonging to the display without showing the
black bars.