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HMP8156CN Datasheet(PDF) 3 Page - Intersil Corporation |
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HMP8156CN Datasheet(HTML) 3 Page - Intersil Corporation |
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3 / 33 page  3 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 config- urable 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. 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 2. 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. Input Processing COLOR SPACE CONVERSION For linear RGB input formats, the encoder applies gamma- correction using a selectable gamma value of 1/2.2 or 1/2.8. The gamma-corrected RGB data from either the correction function in linear mode or the input port otherwise is con- verted to 4:4:4 sampled YCbCr data. For the YCbCr input formats, the encoder converts the 4:2:2 sampled data to 4:4:4 sampled data. The conversion is done by 2x upsampling the Cb and Cr data. The upsampling func- tion uses linear interpolation. OVERLAY PROCESSING The HMP8156 accepts overlay data via the OL0-OL2, M0, and M1 pins. Overlay mixing is done using the 4:4:4 YCbCr pixel data from the color space converter. The YCbCr data following overlay processing is used as input data by the video processing functions. The OL0-OL2 inputs select the color to be mixed with the pixel data. Overlay colors 1-7 are standard color bar colors. Overlay color 0 is special and disables mixing on a pixel by pixel basis. The overlay color palette is shown in Table 1. Note that overlay capability is not available when the 24-bit RGB input format is used. The encoder provides 4 methods for mixing the overlay data with the pixel data: disabled, external mixing, internal mixing and no mixing. The method used is selected in the input for- mat control register. Overlay Mixing: Disabled When overlay mixing is disabled, the OL0-OL2, M0, and M1 inputs are ignored and the pixel data is not changed. TABLE 1. OVERLAY COLOR PALETTE OL2-OL0 COLOR 000 001 010 011 100 101 110 111 Pixel Data 75% Blue 75% Red 75% Magenta 75% Green 75% Cyan 75% Yellow 100% White HMP8156 |
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