bt829bkrf ETC-unknow, bt829bkrf Datasheet - Page 53

• Manufacturer Part Number: bt829bkrf
• Description: Video Streamii Decoders
• Manufacturer: ETC-unknow

Bt829B/827B
VideoStream II Decoders
1.10.1 Automatic Chrominance Gain Control
1.10.2 Low Color Detection and Removal
data is immediately placed in the CC_DATA and CC_STATUS registers and is
available to be read. Once the data is read from the CC_DATA register, the infor-
mation in the next location of the FIFO is placed in the CC_DATA and
CC_STATUS registers.
for a sufficiently long period of time, then the CC/EDS FIFO will become full and
the Bt829B will not be able to write additional data to the FIFO. Any incoming
bytes of data will be lost and an overflow condition will occur; bit OR in the
CC_STATUS register will be set to a logical 1. The system may clear the overflow
condition by reading the CC/EDS data and creating space in the FIFO for new
information. As a result, the overflow bit is reset to a logical 0.
The writes will be from the CC/EDS circuitry and the reads will occur as the sys-
tem controller reads the CC/EDS data from Bt829B. These reads and writes will
sometimes occur simultaneously, and the Bt829B is designed to give priority to
the read operations. In the case where the CC_DATA register data is specifically
being read to clear an overflow condition, the simultaneous occurrence of a read
and a write will not cause the overflow bit to be reset, even though the read has
priority. An additional read must be made to the CC_DATA register in order to
clear the overflow condition. As always, the write data will be lost while the FIFO
is in overflow condition.
CC_STATUS register; any data in the FIFO is lost.
The Automatic Chrominance Gain Control (ACGC) compensates for reduced
chrominance and color-burst amplitude. This can be caused by high-frequency
loss in cabling. Here, the color-burst amplitude is calculated and compared to
nominal. The color-difference signals are then increased or decreased in ampli-
tude according to the color-burst amplitude difference from nominal. The maxi-
mum amount of chrominance gain is 0.5–2 times the original amplitude. This
compensation coefficient is then multiplied by the value in the Saturation Adjust
Register for a total chrominance gain range of 0–2 times the original signal. Auto-
matic chrominance gain control may be disabled by setting the ACGC bit in the
SCLOOP register to a logical 0.
If a color burst of 25 percent (NTSC) or 35 percent (PAL/SECAM) or less of the
nominal amplitude is detected for 127 consecutive scan lines, the color-difference
signals U and V are set to zero. When the low color detection is active, the
reduced chrominance signal is still separated from the composite signal to gener-
ate the luminance portion of the signal. The resulting Cr and Cb values are 128.
Output of the chrominance signal is re-enabled when a color burst of 43 percent
(NTSC) or 60 percent (PAL/SECAM) or greater of nominal amplitude is detected
for 127 consecutive scan lines.
the SCLOOP register (0x10) to a logical 0.
When the first byte of CC/EDS data is decoded and stored in the FIFO, the
If the controller in the system ignores the Bt829B CC_VALID interrupts pin
There will routinely be asynchronous reads and writes to the CC/EDS FIFO.
The FIFO is reset when both CC and EDS bits are disabled in the
Low color detection and removal may be disabled by setting the CKILL bit in
D829BDSA
1.10 Closed Captioning and Extended Data Services Decoding
1.0 Functional Description
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