HMP8156 Intersil Corporation, HMP8156 Datasheet - Page 5

• Manufacturer Part Number: HMP8156
• Description: Ntsc/pal Encoder
• Manufacturer: Intersil Corporation

In external mixing mode, there is no minimum number of pix-
els an overlay color or pixel color must be selected. The mix-
ing level may also vary at any rate.
Overlay Mixing: Internal
Mixing of overlay and pixel data may also be controlled inter-
nally, and the M1 and M0 input pins are ignored. A transition
from pixel data to overlays, from overlays to pixel data, or
between different overlay colors triggers the mixing function.
An overlay color must be selected for a minimum of three
pixels for proper overlay operation in this mode. Internal
overlay mixing should not be used with the BT.656 input for-
mat.
When going from pixel to overlay data, mixing starts one pixel
before the selection of the overlay color (OL2-OL1!= 000). The
first pixel output before the overlay uses 12.5% overlay color
plus 87.5% pixel color. The next output is aligned with the
selection of the overlay color and uses 87.5% overlay color
plus 12.5% pixel color. Additional outputs use 100% overlay
color.
When going from overlay to pixel data, mixing starts one
pixel before the selection of the pixel color (OL2-OL0 = 000).
The last pixel output of the overlay uses 87.5% overlay color
plus 12.5% pixel color. The next output uses 12.5% overlay
color plus 87.5% pixel color. Additional outputs use 100%
pixel color.
When going from one overlay color to another, mixing starts
one pixel before the selection of the new overlay color, and
uses 12.5% new overlay color plus 87.5% old overlay color.
The next output is aligned with the selection of the new over-
lay color and uses 87.5% new overlay color plus 12.5% old
overlay color. Additional outputs use 100% new overlay
color.
Overlay Mixing: No Mixing
With no overlay mixing selected, whenever the OL0-OL2
inputs are non-zero, the overlay color is displayed. The M0
and M1 inputs are ignored, and no internal mixing is done.
Essentially, this is a hard switch between overlay and pixel
data. In this mode, there is no minimum number of pixels an
overlay color or pixel color must be selected.
2X Upscaling
Following overlay processing, 2X upscaling may optionally
be applied to the pixel data. In this mode, the HMP8156
accepts SIF resolution video at 50 or 59.94 frames per sec-
ond and generates standard interlaced video at 262.5 lines
per field (240 active) at 59.94 fields per second for (M,
NSM) NTSC and (M) PAL, and 312.5 lines per field (288
active) at 50 fields per second for (B, D, G, H, I, N, CN) PAL.
M1, M0
00
01
10
11
TABLE 3. OVERLAY MIXING FACTORS
% OVERLAY
COLOR
12.5
87.5
100
0
% PIXEL
COLOR
87.5
12.5
100
0
HMP8156
5
This mode of operation allows SIF video to be upscaled to
full resolution and recorded on a VCR or displayed on a TV.
The input pixel data rate is reduced by half when 2X upscal-
ing is enabled. The color space conversion generates, and
the overlay mixer uses, 2:2:2 YCbCr data instead of 4:4:4
data. For rectangular pixel NTSC and PAL video, the input
rate is 6.75MHz during the active portion of each line instead
of 13.5MHz. Example SIF input resolutions and resulting
output resolutions are shown in Table 4.
The HMP8156 performs horizontal 2X upscaling by linear
interpolation. The vertical scaling is done by line duplication.
For typical line duplication, the same frame of SIF pixel input
data is used for both the odd and even fields. Note that a
frame of SIF size input has about the same number of lines
as a field of full size input. After 2X upscaling, the input is
4:4:4 YCbCr data ready for video processing.
Pixel Input and Control Signal Timing
The pixel input timing and the video control signal input/out-
put timing of the HMP8156 depend on the part’s operating
mode. The periods when the encoder samples its inputs and
generates its outputs are summarized in Table 5.
Figures 1-9 show the timing of CLK, CLK2, BLANK, and the
pixel and overlay input data with respect to each other.
BLANK may be an input or an output; the figures show both.
When it is an input, BLANK must arrive coincident with the
pixel and overlay input data; all are sampled at the same
time.
When BLANK is an output, its timing with respect to the pixel
and overlay inputs depends on the blank timing select bit in
the timing_I/O_1 register. If the bit is cleared, the HMP8156
deasserts BLANK one CLK cycle before it samples the pixel
and overlay inputs. As shown in the timing figures, the
encoder samples the inputs 1-7 CLK2 periods after negating
BLANK, depending on the operating mode.
If the bit is set, the encoder deasserts BLANK during the
same CLK cycle in which it samples the input data. In effect,
the input data must arrive one CLK cycle earlier than when
the bit is cleared. This mode is not shown in the figures.
TABLE 4. TYPICAL RESOLUTIONS FOR 2X UPSCALING
INPUT ACTIVE
RESOLUTION
352 x 240
352 x 288
320 x 240
384 x 288
OUTPUT ACTIVE
RESOLUTION
704 x 480
704 x 576
640 x 480
768 x 576