ml6461 Micro Electronics Corporation, ml6461 Datasheet - Page 20

• Manufacturer Part Number: ml6461
• Description: Ntsc Video Encoder
• Manufacturer: Micro Electronics Corporation

ML6461
FUNCTIONAL DESCRIPTION
Note 1: Ignore first four and last four pixels.
Note 2: Ignore last eight pixels.
20
ANALOG_
smoothing) is done to the beginning and end of the active
portion of the line. When this bit is set (B24=1), the
ML6461 is optimized for "analog" line encoding, where
the number of active pixels is 712 for CCIR656 rates and
640 for square pixel rates. The beginning and end of the
active video portion of the line is tapered (smoothed) to
minimize ringing introduced due to fast transitions. Figure
14 below illustrates the timing comparisons.
Note: For the square pixel rate the only difference
between "analog" and "digital" encoding is the tapering
(smoothing) at the beginning and end of the active video
portion of the line. The number of pixels encoded during
the active video portion is the same in both cases. The
positioning of the active portion is the same as in "analog"
line encoding.
ANALOG_HRESET, B23 This bit is active only in
external slave mode and when the external sync is given
at the beginning of active video. In this mode,
ANALOG_HRESET (B23) must be used in conjunction
with ANALOG_HBLANK (B23) to choose between
"analog" and digital" line encoding. The possible
approaches are summarized in Table 4 below.
HRESET
B23
0
0
1
1
1.56µs
ANALOG_
HBLANK
B24
0
1
0
1
4.7µs
5.3µs
Table 4. Video Encoding Standards and Horizontal/Active Video Timing
Figure 14. Timing of Horizontal Blanking Interval and Active Video
RECOMMENDED
Digital TV Line
Recommended
9µs + 4 PIXELS
ITU-R/SMPTE
ENCODING
ITU-R656
Optional
9µs
9 CYCLES
Analog
Not
(Continued)
TIME BETWEEN
ACTIVE VIDEO
H_SYNC AND
9µs + 4pixels
9µs + 4pixels
= 9.3µs
= 9.3µs
9µs
FULL_BAR, B22 This bit is used to program the ML6461
to encode in normal modes or 100% amplitude video
(100% color bar). When this bit is set (B22=1), the
ML6461 is ready to handle 100% color bars. With 75%
amplitude signals, this bit should be cleared (B22=0) for
optimum signal to noise performance.
JAPAN_BLANK, B21 This bit is used to program the
ML6461 to encode Japanese NTSC by removing the 7.5
IRE setup in blanking and thus boosting the gain of luma
and chroma DACs. This bit is set (B21=1) to handle
Japanese NTSC modes.
WIDE_VBLANK, B20 Determines which lines to blank
at the beginning of each field. For wide blanking, this bit
is set (B20=1), the ML6461 provides 15 lines of blanking.
For narrow blanking, this bit is cleared (B20=0), the
ML6461 provides 9 lines of blanking.
CC_21, B19 This bit enables (B19=1) and disables
(B19=0) the transmission of closed captioning data on
line 21.
CCIR656 ANALOG LINE ENCODING: 712 PIXELS, 1424 TCLKs
CCIR656 DIGITAL LINE ENCODING: 720 PIXELS, 1440 TCLKs
DIGITAL ENCODING: 640 PIXELS, 1280 TCLKs
CCIR 656
See Note 1
See Note 2
720
712
712
SQUARE PIXEL ANALOG AND
ENCODED
PIXELS
SQUARE PIXEL
640
640
640
SMOOTHING
(B24 = 1)
EDGE
none
Yes
Yes