
Philips Semiconductors
Video Out
File: evo.fm5, modified 7/24/99
PRELIMINARY INFORMATION
7-5
7.7.2
CCIR 656 Line Timing
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.
7.7.3
SAV and EAV Codes
The EAV (End Active Video) and SAV (Start Active Vid-
eo) codes are issued at the start of each video line. EAV
and SAV codes have a fixed format: a three-byte pream-
ble of FFh, 00h, 00h followed by the SAV or EAV code
byte. The EAV and SAV code byte format is shown in
fine the start and end of the horizontal blanking interval,
and they also indicate the current field number and the
vertical blanking interval.
The SAV and EAV codes have a four-bit protection field
to insure valid codes. The VO generates these protection
bits as part of the SAV and EAV codes as defined by
CCIR656. There are eight possible valid SAV and EAV
codes. These eight codes with their correct protection
bits are shown in
Table 7-2. The VO generates SAV and
EAV sync codes and inserts them into the video out data
stream according to the CCIR656 specification under all
conditions, whether it is generating or receiving horizon-
tal and frame timing information.
7.7.4
F0h and 10h Video Clamps
SAV and EAV codes are identified by a three-byte pre-
amble of FFh, 00h and 00h. This combination must be
avoided in the video data that the VO sends out to pre-
vent accidental generation of an invalid sync code. The
VO includes maximum and minimum value clamps on
the video data to prevent this possibility. After all internal
processing has been done the VO automatically con-
verts resulting image data values in the range F1h..FFh
to F0h and values in the range 00h..0Fh to 10h.
7.7.5
CCIR 656 Frame Timing
The frame timing for CCIR 656 is shown in
Table 7-3.CCIR 656 defines interlaced frame timing. Lines are
numbered from 1 to 525 for 525-line, 60-Hz systems and
from 1 to 625 for 625-line, 50-Hz systems. The Field and
Vertical Blanking columns indicate whether the field and
vertical blanking bits, respectively, are set in the SAV
and EAV codes for the indicated lines. The 525 and 625
formats have similar timing but differ in their line number.
Table 7-2. SAV and EAV Codes
Code
Binary Value
Field
Vertical Blanking
SAV
1000 0000
1
EAV
1001 1101
1
SAV
1010 1011
1
X
EAV
1011 0110
1
X
SAV
1100 0111
2
ES
S
E
Blanking
Active Video
Blanking
Active Video
Line i
Line i+1
SAV, EAV Codes
YUV 4:2:2 pixels
Figure 7-10. CCIR 656 line timing.
Figure 7-11. Format of SAV and EAV timing codes.
Preamble
11111111
00000000
1 F V H PPPP
Timing reference code
Protection bits
(error correction)
H = 0 for SAV
H = 1 for EAV
V = 1 during field blanking
V = 0 elsewhere
F = 0 during field 1
F = 1 during field 2
EAV
1101 1010
2
SAV
1110 1100
2
X
EAV
1111 0001
2
X
Table 7-3. CCIR 656 Frame Timing
Line Number
F bit
V bit
Comments
525/60
625/50
1–3
624–625
1
Vertical blanking for
eld 1, SAV/EAV code
still indicates eld 2
Table 7-2. SAV and EAV Codes
Code
Binary Value
Field
Vertical Blanking