CX25870/871
1.0 Functional Description
Flicker-Free Video Encoder with Ultrascale Technology
1.3 Device Description
While in CCIR656 Mode, the encoder adheres to all input guidelines specified
in the ITU-R BT.656-3 standard. This specification was developed for the
transmission of color video signals in YCrCb format at a pixel rate of
27.000 MHz without the use of dedicated timing reference signals.
To display a DVD movie on a TV and computer monitor simultaneously with
high-quality MPEG2 image format, the CX25870/871 must be integrated into the
hardware design. Next, actual CCIR656 data must be sent from a MPEG2
decoding master device directly to the CX25870/871 encoder. Finally, various
software steps are necessary so the encoder switches to its Slave interface and is
set up to accept the interlaced YCrCb data and video timing reference codes.
The first programming step is to configure the CX25870/871 to accept
interlaced 4:2:2 YCrCb data with an active resolution of 720x480 and output a
standard NTSC video output. The pertinent set of conditions for this option are:
• Type of Digital Video Input:
• Active Resolution (HorizontalxVertical):
• Overscan Compensation:
• Interface:
Interlaced 4:2:2 YCrCb
720 pixels x 480 lines
None. Horizontal = 0%; Vertical = 0%
CX25870/871 is clock and timing slave
27.000 MHz
• Pixel Rate
• Type of Analog Video Output:
Standard NTSC[NTSC-M]
Given this set of conditions, autoconfiguration mode 28 is a perfect fit. As a
result, simply use the MPEG2 decoders serial bus mastering ability to program
the CX25870/871s CONFIG[5:0] field with a binary value of 011100. This
translates into writing a hexadecimal number of 0x34 to register 0xB8. Once the
encoder acknowledges this write to its autoconfiguration register, it automatically
loads the appropriate values for this type of DVD configuration into its register
indices from 0x76 to 0xB4, including register 0x38. The exact data transferred
into these registers is contained in Appendix C.
After completion of the autoconfiguration command, the encoder expects to
receive interlaced 4:2:2 YCrCb data from the clock and timing master device at a
rate of 27.000 MHz with blanking regions being defined by HSYNC* and
VSYNC*. Since these external signals, by definition, do not exist in CCIR656
mode, a second and final programming step is required.
After enabling autoconfiguration mode 28, the programmer must make sure to
set (=1) the E656 bit. This is bit 6 of register 0xD6 and enables a CCIR656 input
to be received via the CX25870/871s P[7:0] port. Once this is done, the encoder
deciphers digital blanking through the SAV and EAV codes and disregards the
synchronization signals.
Only after the completion of these steps will a DVD stream be properly
encoded and rendered onto the television by the VGA Encoder.
For CCIR Mode operation with a PAL Composite or S-Video output, use
Autoconfiguration Mode 29 instead of autoconfiguration mode 28 and program
the master device to send a digital frame with an active resolution of 720x576.
100381B
Conexant
1-65
CONEXANT [ CONEXANT SYSTEMS, INC ]
