
Philips Semiconductors
Video Out
File: evo.fm5, modified 7/24/99
PRELIMINARY INFORMATION
7-7
reset to their start values when they reach their stop val-
ues; when the VO receives frame timing signals, the
frame counters continue counting until reset by the exter-
nal signals.
The image area is defined by the IMAGE VOFF and IM-
AGE HOFF values. These values are added to the VF1
or F2 VIDEO LINE and VIDEO PIXEL START values to
define the starting line and pixel, respectively of the im-
age area. The image area is active when the contents of
the Frame Line Counter and Frame Pixel Counter equal
or exceed these values.
The Image Line Counter and Image Pixel Counter start
counting at the first active pixel in the image area and the
first active line in the image area, respectively. The im-
age counters start at zero and stop counting when they
reach their image height and width values. The image
counters are reset by frame counter values indicating the
start of the image pixel in a line and the start of the image
line in a field.
The image counters define the active image area of the
frame, the area of interest for image processing. This al-
lows the overlay start address to be defined relative to
the active image area, for example. When the VO is not
sending out active pixels from the image area, it sends
out blanking codes. These blanking codes are (0x80,
0x10, 0x80, 0x10) for each two pixel group in YUV 4:2:2
image data format, as defined by CCIR 656 and shown
7.8.1
Horizontal and Frame Timing Signals
The VO can supply horizontal and frame timing signals
or
receive
a
frame
timing
signal.
When
the
SYNC_MASTER bit is set, the VO generates the hori-
zontal and frame timing for the external video device.
When the SYNC_MASTER bit is cleared, Video Out op-
erates in external sync mode and an external device,
such as a DENC, is responsible for providing frame sync.
If SYNC_MASTER is set, VO_IO1 acts as output and
generates a horizontal timing signal, and VO_IO2 gener-
generated signals relate to the VO line and field timing.
The horizontal timing signal corresponds to the horizon-
tal-blanking interval, and the frame timing signal corre-
sponds to the field-2 active interval. The horizontal timing
signal is active low from the EAV code at the start of the
line to the SAV code at the start of active video for the
line. The frame timing signal is active high from the EAV
code that begins the first line of vertical blanking for field
2 to the EAV code that begins the first line of blanking for
field 1. Note: The VO_IO2 signal does not take the F1
and F2 overlap regions into account and therefore differs
from the field value indicated by the SAV and EAV codes
during the overlap times.
If SYNC_MASTER is clear, VO expects frame timing sig-
nals on the VO_IO2 pin. The active edge of the signal
can be programmed using VO_IO2_POS. The selected
transition of the frame timing signal on VO_IO2 causes
the Frame Line Counter to be set to the FRAME PRE-
SET value and video output to start. Horizontal sync start
is taken from the transition on VO_IO2, and generated
internally subsequently. Note: due to implementation lim-
itations FRAME PRESET must be 1. Due to implemen-
tation limitations this works only once after reset. To con-
tinuously use this genlock feature, a periodic software
reset is required.
7.9
DATA TRANSFER TIMING
In the
data streaming and message passing modes, the
VO supplies a stream of 8-bit data. No data selection or
data interpretation is done, and data is transferred at one
byte per VO_CLK. Data is clocked out on the positive
edge of VO_CLK.
The message passing mode issues signals on VO_IO1
and VO_IO2 to indicate the start and end of the mes-
sage. The timing for these signals is shown in
Image Line: Image Width
Blanking
Image Width, Pixels
Field Width, Pixels
SAV
EAV
Image Data
EAV
Blanking
Field 1
Field 2
V Blanking
Frame Height, Lines (2 fields)
VO_IO2
Image Data
V Blanking
Field 1
Field 2
Figure 7-13. Horizontal and vertical timing signals given as output.