TM1100 Preliminary Data Book
Philips Semiconductors
7-6
PRELIMINARY INFORMATION
File: evo.fm5, modified 7/24/99
7.8
VIDEO OUT TIMING GENERATION
The VO generates timing for frames, active video areas
within frames, images within the active video area, and
overlays within the image area. The relationship between
the timing for both interlaced fields. Progressive scan, or
non-interlaced video, is accomplished by setting the tim-
ing parameters such that 2 identical successive fields are
generated.
The active image area begins after the horizontal and
vertical blanking intervals and represents the pixels that
are visible on the screen. The image area is the actual
displayed image within the active video area. It can be
slightly smaller than the active video area to avoid edge
effects at the top, bottom and sides of the image. The
overlay area is within the image area.
The VO uses two sets of counters to generate and con-
trol image timing: frame counters and image counters.
The Frame Line Counter and Frame Pixel Counter con-
trol the overall timing for the frame and define the total
number of pixels per line, lines per frame and interlace
timing, including horizontal and vertical blanking inter-
vals. Note that the Frame Line Counter has a starting val-
ue of one, not zero, and it counts from 1 to 525 or 625,
consistent with CCIR 656 line numbering. The Image
Line Counter and Image Pixel Counter define the visible
image within the field.
The geometry of active video is defined by the contents
2 START value defines the start line of field 2. Field 2 is
active when the Field Line Counter contents equal or ex-
ceed this value. The active video area is defined by the
F1 VIDEO LINE and F2 VIDEO LINE values for each
field of the frame and VIDEO PIXEL START value for
each line of the frame. The active video area begins
when the contents of the Frame Line Counter and Frame
Pixel Counter equals or exceeds these values.
The CCIR 656 compliant 525/60 and 625/50 timing spec-
ifications define an overlap period where the field num-
ber in the SAV and EAV codes from field 1 persist into
the vertical blanking interval for field 2, and the codes for
field 2 persist into the vertical blanking interval for field 1.
The F1 OLAP and F2 OLAP values define these overlap
intervals. During the overlap interval, the vertical blank-
ing for the next field has begun; however, the field num-
ber flag in the SAV and EAV codes still shows the field
number for the previous field. The field number is updat-
ed to the correct field value at the end of the overlap in-
terval.
F1 OLAP defines the overlap from field 1 to field 2. This
overlap occurs during the beginning of vertical blanking
for field 2; The SAV and EAV codes continue to show
field 1 during this overlap interval, and they change to
field 2 at the end of the interval.
F2 OLAP defines the overlap from field 2 to field 1. This
overlap occurs during the beginning of vertical blanking
for field 1; The SAV and EAV codes continue to show
field 2 during this overlap interval, and they change to
field 1 at the end of the interval.
F1 OLAP and F2 OLAP are small two’s complement val-
ues in the range -8 .. +7 . A positive value indicates that
the overlap extends into the current field, while a nega-
tive value indicates that it extends backward into the pre-
vious field. See
Figure 7-26 for the effect of negative and
positive values.
The frame and image counters have different start and
stop points. The frame counters begin in the vertical
blanking interval of the first field and the horizontal blank-
ing interval of the first line. They stop counting when they
reach the height and width values of the frame. When the
VO generates the frame timing, the frame counters are
4–19
1–22
0
1
Vertical blanking for
eld 1, change SAV/
EAV code to eld 1
20–263
23–310
0
Active video, eld 1
264–265
311–312
0
1
Vertical blanking for
eld 2, SAV/EAV code
still indicates eld 1
266–282
313–335
1
Vertical blanking for
eld 2, change SAV/
EAV code to eld 2
283–525
336–623
1
0
Active video, eld 2
Table 7-3. CCIR 656 Frame Timing
Line Number
F bit
V bit
Comments
525/60
625/50
Overlay
Image Area, Field 1
Vertical Blanking, Field 1
Horizontal
Blanking
Overlay
Image Area, Field 2
Vertical Blanking, Field 2
Horizontal
Blanking
Image V Offset
Image
H
Offset
Image
H
Offset
Image Width
Image
Height
Frame
Active Video Area
Start Pixel
Start
Line
Figure 7-12. Frame, field, active video, image, and
overlay definitions.