CX25870/871
1.0 Functional Description
Flicker-Free Video Encoder with Ultrascale Technology
1.3 Device Description
After completion of the autoconfiguration command, the encoder enters
Master interface. In addition, the CX25870/871 will expect to receive digital
frames with an active resolution of 720x480 comprised of noninterlaced RGB
data at a pixel rate of 27.6923 MHz. If these events occur, approximately 40
clocks later (i.e., pipeline delay), the encoder will begin transmitting a
NTSC-compliant S-Video or Composite video signal containing the DVD movie.
1.3.40 SECAM Output
Unlike its predecessor, the Bt868/869, the CX25870/871 now includes an encoder
block for conversion of digital video data into a SECAM Composite (CVBS)
and/or a SECAM S-Video signal.
Like other video outputs, any active resolution from 320x200 to 1024x768 can
be supported with the SECAM encoder block. The circuit accepts RGB or YCrCb
data in a variety of multiplexed or nonmultiplexed input formats, reformats the
digital data, and finally routes the stream through the four on-chip
Digital-to-Analog Converters (DACs). The encoder supports all variations of the
SECAM analog video standard including those commonly used in France
(SECAM-L), Eastern Europe/Russia (D, K, K1), and Greece/Middle East (B, G, H).
The SECAM specific processing is achieved in this block by a pre-emphasis
of the color difference signals. Once data is received, it is converted to an internal
YUV format. Next, the Y component is filtered and then upsampled to the system
clock frequency while the UV components are used to frequency modulate the
two subcarrier frequencies appropriately.
The luminance signal is always low-pass filtered using the upsampling filter
response illustrated in Figure 1-24. Additional peaking or reduction filters can be
enabled (see Figures 1-25 through 1-27), using the PKFIL_SEL[1:0] bit field.
The peaking filters are optimized for a high bandwidth frequency response and
optimal picture quality.
The default chrominance filter response is illustrated in Figure 1-28, but an
alternate wide bandwidth response can be selected by setting register bit
CHROMA_BW, as illustrated in Figure 1-29. The color subcarrier frequencies,
4.25000 MHz for Db and 4.40625 MHz for Dr, are controlled by a number of
registers, chiefly MSC_DB[31:0] for Db and MSC[31:0] for Dr. Figure 1-30
illustrates the SECAM pre-emphasis filter response at higher (>3 MHz)
frequencies within the standard definition television passband.
Table 1-21 lists three complete register sets for the most common desktop
input resolutions with the SECAM output. This output adheres to the SECAM
target video parameters included in Table A-1. This occurs only if the Conexant
encoder is programmed correctly with the register values listed in Table 1-21, the
master device provides the RGB data at the listed clock frequency (CLKI/CLKO),
and the interface bits are modified to match the desired connection type.
100381B
Conexant
1-69
CONEXANT [ CONEXANT SYSTEMS, INC ]
