2.0 Functional Description
Fusion 878A
2.1 UltraLock
TM
Functionality
PCI Video Decoder
2-2
Conexant
100600B
pixels per line. UltraLock then interpolates the required number of pixels in a way
that maintains the stability of the original image despite variation in the line
length of the incoming analog waveform.
illustrates an example of three successive lines of video being
decoded for square pixel NTSC output. The first line is shorter than the nominal
NTSC line time interval of 63.5
µ
s. On this line, a line time of 63.2
µ
s sampled at
4 × Fsc (14.31831 MHz) generates only 905 pixels. The second line matches the
nominal line time of 63.5
µ
s and provides the expected 910 pixels. Finally, the
third line is too long at 63.8 µs within which 913 pixels are generated. In all three
cases, UltraLock outputs only 780 pixels.
UltraLock can be used to extract any programmable number of pixels from the
original video stream as long as the sum of the nominal pixel line length (910 for
NTSC and 1,135 for PAL/SECAM) and the worst case line length validation from
nominal in the active region is greater than or equal to the required number of
output pixels per line; i.e.,
NOTE:
With stable inputs, UltraLock guarantees the time between the falling
edges of HRESET to within only one pixel. UltraLock does, however,
guarantee the number of active pixels in a line as long as the above
relationship holds.
Figure 2-1. UltraLock Behavior for NTSC Square Pixel Output
Analog
Waveform
63.2
µ
s
63.5
µ
s
63.8
µ
s
905 pixels
910 pixels
913 pixels
Line
Length
Pixels
Per Line
780 pixels
780 pixels
780 pixels
Pixels
Sent to
the FIFO
by
UltraLock™
879A_005
P
No m
P
Va r
+
P
Desired
≥
where:
P
Nom
= Nominal number of pixels per line at 4 × Fsc sample rate
(910 for NTSC, 1,135 for PAL/SECAM)
P
Var
= Variation of pixel count from nominal at 4 × Fsc (can be
a positive or negative number)
P
Desired
= Desired number of output pixels per line
