bt865a Conexant Systems, Inc., bt865a Datasheet - Page 32

• Manufacturer Part Number: bt865a
• Description: Ycrcb To Ntsc/pal Digital Video Encoder
• Manufacturer: Conexant Systems, Inc.

Circuit Description
1.6
1.7
1.7.1
1-22
YC Inputs (4:2:2 YCrCb)
Power Saving Modes
Pixel Input Ranges and Colorspace Conversion
In SLEEP power-down mode (SLEEP pin set to 1), all analog and digital circuitry is
disabled, and total device current consumption approaches 0 mA. Register states are
preserved, but other chip functionality (including I
This mode should be set when the Bt864A/Bt865A may be subjected to clock and
data frequencies outside its functional range.
In DACOFF power-down mode, (DACOFF register is set to 1) all DACs are disabled
and analog current is reduced to approximately 0 mA. All other digital circuitry
remains operational, permitting system timing and other functions to continue.
When DACs are disabled by either SLEEP or DACOFF, VREF will go to approximately
0.5 V below VAA.
Y has a nominal range of 16–235; Cb and Cr have a nominal range of 16–240, with
128 equal to zero. Values of 0 and 255 are interpreted as 1 and 254, respectively. Y
values of 1–15 and 236–254, and CrCb values of 1–15 and 241–254, are interpreted as
valid linear values.
The SETUPDIS bit will alter pixel scaling and disable or enable the 7.5 IRE setup.
When this bit is enabled, PAL–B, D, G, H, I, N, Nc video can be generated using
NTSC/PAL–M blanking levels and 7.5 IRE setup, and NTSC/PAL–M pixel scaling is
performed (Y range of 16–235 represents 7.5–100 IRE); or, NTSC/PAL–M video can
be generated using PAL–B, D, G, H, I, N, Nc scaling (Y range of 16–235 represents
0–100 IRE) without the 7.5 IRE setup. NTSC/PAL–M mode with setup disabled has
2% less black-to-white range than NTSC/PAL–M mode with setup enabled.
For RGBOUT mode, 4:2:2 YCrCb digital component video will be upsampled to
4:4:4 and used to generate composite video and will be converted to the RGB
colorspace to drive the RGB DACs. The Y input range of 16–235 will produce a range
of 0.7 V at the output. Since YC values outside of the nominal range are allowed, the
black level is raised above zero volts to allow for Y values less than 16, and the output
range of the DACs can exceed 0.7 V to allow for Y values above 235. The conversion
is linearly scaled in the overshoot and undershoot regions. The following matrix,
based on CCIR601, is used to convert YCrCb to RGB:
Values are rounded to 9 bits at the DAC.
R = Y + 1.371*Cr
G = Y – 0.699*Cr – 0.337*Cb
B = Y + 1.733*Cb
Conexant
2
C communication) is disabled.
Bt864A/Bt865A Data Sheet
100138C
02/17/03