mc44724 Freescale Semiconductor, Inc, mc44724 Datasheet - Page 11

• Manufacturer Part Number: mc44724
• Description: Digital Video Encoder
• Manufacturer: Freescale Semiconductor, Inc

CVBS and S-VIDEO or YCbCr or RGB Outputs
The internal digital video signals drive 10-bit D/A converters. Converter outputs are bi-directional current
sources where the current is proportional to the digital data with reference to the IBIAS reference current. The
pins CVBS/Cb/B, Y/G and C/Cr/R are the respective composite, Luma and Chroma or Y/Cb/Cr or R/G/B signal
current source pins. Also, each DACs can drive 75ohm load register.
User can select 2 sets of signals within above 3 sets.
(see "Application Diagram" and "sub-address register descriptions".)
Bias Current Gain
DACs can be switched off through serial bus control to reduce power consumption. Both outputs of unused
DACs should be connected to ground through a resister to avoid charge buildup.
Chroma / Luma Encoding
The DVE de-multiplexes the 4:2:2 digital video data stream.
The de-multiplexed Y or Luma samples are interpolated (2X oversampled) at the clock rate. Offset
compensation is then added, next any VBI signals consisting of Closed-Caption, CGMS and WSS are
added to the appropriate lines, then finally composite sync pulses are added to the Luma signal.
De-multiplexed component color CB and CR samples are interpolated (4X oversampled) at the clock rate.
Interpolating simplifies the output filter and allows more accurate encoding. The DVE generates the
necessary subcarrier color frequency for PAL or NTSC encoding from the 27Mhz system clock. This
color subcarrier is then modulated by the base band component color CB and CR signals to create the
video Chroma signal. (see figure 13.)
A 7.5 IRE pedestal is added for the 60Hz field rate. This can be added for the 50Hz field rate through
serial bus control.
(see figure 12.)
This document contains information on a new product. Specifications and information herein are subject to change without notice.
(see sub-address register descriptions)
No.
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MC44724/5 Rev 0.21 03/25/97