PNX1300/01/02/11 Data Book
Philips Semiconductors
7-4
PRELIMINARY SPECIFICATION
90 MHz. The PLL is enabled and programmed as de-
scribed in
Section 7.19
.
DDS clock rate is set by the VO_CLOCK. FREQUENCY
field according to the equation shown in
Figure 7-6
. The
VO_CLK frequency can be a divider or multiplier of
f
DDS
,
as determined by the PLL subsystem settings.
Low-jitter clock mode is automatically entered whenever
FREQUENCY[31] = 1. If FREQUENCY[31] = 0, the DDS
operates at 1/3 the rate (for compatibility with TM-1000
code), and FREQUENCY must be set as shown in
Figure 7-7
.
The DDS synthesizer maximum jitter can be computed
as follows:
9
f
DSPCPU
Example of jitter values can be found in
Table 7-2
.
7.8
IMAGE TIMING
The EVO emits a serial byte-data stream used by
CCIR 656 devices to generate a displayed image.
Figure 7-9
shows an NTSC-compatible, 525-line inter-
laced image. The field and line numbers are shown for
reference.
Interlaced images are generated by the display hardware
by controlling the vertical retrace timing. For reference,
Figure 7-8
shows a timing diagram of NTSC-compatible
interlaced frame timing illustrating the analog vertical re-
trace signal. The vertical retrace signal for the second
field begins in the middle of the horizontal line that ends
the first field. This causes the first line of the second field
to begin halfway across the display screen and the lines
of the second field to be scanned between the lines of the
first field, resulting in an interlaced display.
The analog timing required to generate the interlaced
signal is supplied by the display device. The CCIR 656
digital video signals generated by the EVO use frame
synchronization timing and do not generate any vertical
retrace timing.
7.8.1
CCIR 656 Pixel Timing
The EVO generates pixels according to CCIR 656 timing
in YUV 4:2:2 co-sited format and outputs these pixels as
shown in
Figure 7-10
. Pixels are generated in groups of
two, with four bytes per two pixels. Each pair of pixels
has two luminance bytes (Y0, Y1) and one pair of chromi-
nance bytes (U0, V0) arranged in the sequence shown.
The chrominance samples U0 and V0 are sampled spa-
tially co-sited with luminance sample Y0. For PAL or
NTSC video, pixels are generated at a nominal rate of
13. 5 Mpix/sec. (27 MB/sec.). Pixels are clocked out on
the positive edge of VO_CLK.
7.8.2
CCIR 656 Line Timing
The CCIR 656 line timing is shown in
Figure 7-11
. Each
line begins with an EAV code, a blanking interval and an
SAV code, followed by the line of active video. The EAV
code indicates end of active video for the previous line,
and the SAV code indicates start of active video for the
current line.
Table 7-2. Jitter values for common DSPCPU MHz
f
DSPCPU
(MHz)
jitter
(nSec)
f
DSPCPU
(MHz)
jitter
(nSec)
143
166
0.777
0.669
180
200
0.617
0.555
Figure 7-6. DDS low-jitter oscillator frequency.
2
31
f
2
32
9
f
DSPCPU
----------------------------
+
=
Figure 7-7. DDS slow speed oscillator frequency
FREQUENCY
f
2
32
3
f
DSPCPU
----------------------------
=
jitter
-------------1
=
1
19 20
262 263
282
525 1
One Frame
One Line
Field 2
Field 1
Blanking
Blanking
Active Video
Active Video
1/2 Line Interlace Offset
Vertical
Sync
Video
Lines
Figure 7-8. Interlaced timing
—
NTSC analog sync. signals.