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ADV473 Datasheet(PDF) 6 Page - Analog Devices |
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ADV473 Datasheet(HTML) 6 Page - Analog Devices |
6 / 12 page ADV473 –6– REV. A CIRCUIT DESCRIPTION MPU Interface The ADV473 supports a standard MPU bus interface, allowing the MPU direct access to the color palette RAM and overlay color registers. Three address decode lines, RS0–RS2, specify whether the MPU is accessing the address register, the color palette RAM, the overlay registers, or read mask register. These controls also determine whether this access is a read or write function. Table I illustrates this decoding. The 8-bit address register is used to address the contents of the color palette RAM and overlay registers. Table I. Control Input Truth Table RS2 RS1 RS0 Addressed by MPU 0 0 0 Address Register (RAM Write Mode) 0 1 1 Address Register (RAM Read Mode) 0 0 1 Color Palette RAM 0 1 0 Pixel Read Mask Register 1 0 0 Address Register (Overlay Write Mode) 1 1 1 Address Register (Overlay Read Mode) 1 0 1 Overlay Registers 1 1 0 Command Register Color Palette Writes The MPU writes to the address register (selecting RAM write mode, RS2 = 0, RS1 = 0 and RS0 = 0) with the address of the color palette RAM location to be modified. The MPU performs three successive write cycles (8 or 6 bits each of red, green, and blue), using RS0–RS2 to select the color palette RAM (RS2 = 0, RS1 = 0, RS0 = 1). After the BLUE write cycle, the three bytes of color information are concatenated into a 24-bit word or an 18-bit word and written to the location specified by the address register. The address register then increments to the next location which the MPU may modify by simply writing an- other sequence of red, green, and blue data. A complete set of colors can be loaded into the palette by initially writing the start address and then performing a sequence of RED, GREEN and BLUE writes. The address automatically increments to the next highest location after a BLUE write. Color Palette Reads The MPU writes to the address register (selecting RAM read mode, RS2 = 0, RS1 = 1 and RS0 = 1) with the address of the color palette RAM location to be read back. The contents of the palette RAM are copied to the RED, GREEN and BLUE regis- ters and the address register increments to point to the next pal- ette RAM location. The MPU then performs three successive read cycles (8 or 6 bits each of red, green, and blue), using RS0–RS2 to select the color palette RAM (RS2 = 0, RS1 = 0, RS0 = 1). After the BLUE read cycle, the 24/18 bit contents of the palette RAM at the location specified by the address register is loaded into the RED, GREEN and BLUE registers. The ad- dress register then increments to the next location which the MPU can read back by simply reading another sequence of red, green, and blue data. A complete set of colors can be read back from the palette by initially writing the start address and then performing a sequence of RED, GREEN and BLUE reads. The address automatically increments to the next highest location after a BLUE read. 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. COMPOSITE SYNC SIGNAL (SYNC) The position of the composite video signal which synchronizes the scanning process. COMPOSITE VIDEO SIGNAL The video signal with or without setup, plus the composite SYNC signal. 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 to 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. SETUP The difference between the reference black level and the blank- ing level. SYNC LEVEL The peak level of the composite SYNC signal. VIDEO SIGNAL That portion of the composite video signal which varies in gray scale levels between reference white and reference black. Also referred to as the picture signal, this is the portion which may be visually observed. |
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