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ADV101 Datasheet(PDF) 6 Page - Analog Devices |
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ADV101 Datasheet(HTML) 6 Page - Analog Devices |
6 / 12 page ADV101 –6– REV. B TERMINOLOGY Blanking Level The level separating the SYNC portion from the video portion of the waveform. Usually referred to as the front porch or back porch. At 0 IRE units, it is the level which will shut off the pic- ture tube, resulting in the blackest possible picture. Color Video (RGB) This usually refers to the technique of combining the three pri- mary colors of red, green and blue to produce color pictures within the usual spectrum. In RGB monitors, three DACs are required, one for each color. Sync Signal (SYNC) The position of the composite video signal which synchronizes the scanning process. Gray Scale The discrete levels of video signal between reference black and reference white levels. An 8-bit DAC contains 256 different lev- els, while a 6-bit DAC contains 64. Raster Scan The most basic method of sweeping a CRT one line at a time to generate and display images. Reference Black Level The maximum negative polarity amplitude of the video signal. Reference White Level The maximum positive polarity amplitude of the video signal. Sync Level The peak level of the SYNC signal. Video Signal That portion of the composite video signal which varies in gray scale levels between reference white and reference black. Also re- ferred to as the picture signal, this is the portion which may be visually observed. CIRCUIT DESCRIPTION AND OPERATION The ADV101 contains three 8-bit D/A converters, with three input channels, each containing an 8-bit register. Also inte- grated on board the part is a reference amplifier and CRT con- trol functions BLANK, SYNC and REF WHITE. Digital Inputs 24-bits of pixel data (color information) R0–R7, G0–G7 and B0–B7 are latched into the device on the rising edge of each clock cycle. This data is presented to the three 8-bit DACs and is then converted to three analog (RGB) output waveforms. (See Figure 2.) Three other digital control signals are latched to the analog video outputs in a similar fashion. BLANK, SYNC and REF WHITE are each latched on the rising edge of CLOCK to maintain synchronization with the pixel data stream. The BLANK and SYNC functions allow for the encoding of these video synchronization signals onto the RGB video output. This is done by adding appropriately weighted current sources to the analog outputs, as determined by the logic levels on the BLANK and SYNC digital inputs. Figure 3 shows the analog output, RGB video waveform of the ADV101. The influence of SYNC and BLANK on the analog video waveform is illustrated. The REF WHITE control input drives the RGB video outputs to the white level. This function could be used to overlay a cur- sor or crosshair onto the RGB video output. Table I details the resultant effect on the analog outputs of BLANK , SYNC and REF WHITE. All these digital inputs are specified to accept TTL logic levels Clock Input The CLOCK input of the ADV101 is typically the pixel clock rate of the system. It is also known as the dot rate. The dot rate and hence the required CLOCK frequency, will be determined by the on-screen resolution, according to the following equation. Dot Rate = (Horiz Res) × (Vert Res) × (Refresh Rate)/ Dot Rate = (Retrace Factor) Horiz Res = Number of pixels/line Vert Res = Number of lines/frame Refresh Rate = Horizontal Scan Rate. This is the rate at which the screen must be refreshed, typi- cally 60 Hz for a noninterlaced system or 30 Hz for an interlaced system. Retrace Factor = Total blank time factor. This takes into ac- count that the display is blanked for a certain fraction of the total duration of each frame (e.g., 0.8). CLOCK DATA ANALOG OUTPUTS (IOR, IOG, IOB, I ) SYNC DIGITAL INPUTS (R0–R7, G0–G7, B0–B7; SYNC, BLANK, REFWHITE) Figure 2. Video Data Input/Output OBSOLETE |
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