HMP8156 Intersil Corporation, HMP8156 Datasheet - Page 3

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

Functional Operation
The HMP8156 is a fully integrated digital encoder. It accepts
digital video input data and generates four analog video out-
put signals. The input data format is selectable and includes
YCbCr, RGB, and overlay data. The outputs are configurable
to be either two composite video signals and Y/C (S-Video)
or one composite and component RGB video.
The HMP8156 accepts pixel data in one of several formats
and transforms it into 4:4:4 sampled luminance and chromi-
nance (YCbCr) data. If enabled, the encoder also mixes
overlay data with the input data. The encoder then interpo-
lates the YCbCr data to twice the pixel rate and low pass fil-
ters it to match the bandwidth of the video output format. If
enabled, the encoder also adds Closed Captioning informa-
tion to the Y data. At the same time, the encoder modulates
the chrominance data with a digitally synthesized subcarrier.
Finally, the encoder outputs the luminance, chrominance,
and their sum as analog signals using 10-bit D/A converters.
The HMP8156 provides operating modes to support all ver-
sions of the NTSC and PAL standards and accepts full and
SIF size input data with rectangular (ITU-R BT.601) and
square pixel ratios. It operates from a single clock at twice
the pixel clock rate determined by the operating mode.
The HMP8156’s video timing control is flexible. It may oper-
ate as the master generating the system’s video timing con-
trol signals or it may accept external timing controls. The
polarity of the timing controls and the number of active pixels
and lines are programmable.
HMP8156
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Pixel Data Input Formats
The HMP8156 accepts pixel data via the P0-P23 input pins.
The definition of each pixel input pin is determined by the
input format selected in the input format register. The defini-
tion for each mode is shown in Table 1.
YCbCr Pixel Data
The HMP8156 accepts 4:2:2 sampled YCbCr input data.
The luminance and color difference signals are each 8 bits,
scaled 0 to 255. Values outside their nominal ranges (16-235
for Y and 16-240 for Cb and Cr) are processed normally. The
color difference signals are time multiplexed into one 8-bit
bus beginning with a Cb sample. The Y and CbCr busses
may be input in parallel (16-bit mode) or may be time multi-
plexed and input as a single bus (8-bit mode). The single bus
may also contain SAV and EAV video timing reference codes
(ITU-R BT.656 mode).
RGB Data
The HMP8156 accepts 4:4:4 sampled RGB component
video input data. The color signals may be (8,8,8) for 24-bit
mode or (5,6,5) for 16-bit mode. In 24-bit mode, they are
scaled 0 to 255, black to white. In 16-bit mode, the encoder
left shifts the input so that it has the same scale as 24-bit
input. The RGB data may be linear or gamma corrected; if
enabled, the encoder will gamma correct the input data.
Overlay Data
The HMP8156 accepts 5 bits of pixel overlay input data and
combines it with the input pixel data. The data specifies an
overlay color and the fractions of the new and original colors
to be summed.
Blue Screen Generation
In blue screen mode, the HMP8156 ignores the pixel input
data and generates a solid, blue screen. The overlay inputs
may be used to place information over the blue screen.