Importance

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Abstract

A central processing unit (310) in a display system carries pixel-value signals and software-address signals representing the locations of the pixels whose values the pixel-value signals represent. An address-translation circuit (420) converts those software addresses to logical addresses representing the locations of those pixels in a 90.degree.-rotated version of the image that the software address signals represent, and the logical addresses are applied to an image-buffer memory (410) to specify the locations in which to store the pixel values. A refresh-address circuit (620) generates the address signals used in fetching from the image-buffer memory (410) the values that are applied to a display device (360) employed to display the image. The refresh-address generator (620) is operable alternatively in row-forward and row-reverse modes and alternatively in column-forward and column-reverse modes. The addresses represent a sequence of columns across rows and rows across an image, and the column addresses increase within a row in the column-forward mode but decrease in the column-reverse mode. The addresses increase between rows in the row-forward mode and decrease in the row-reverse mode. The effect of the different modes is to compensate for reversals such as mirror-image scans and to convert the 90.degree. rotation between clockwise and counterclockwise.

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First Claim