This register contains the modulo for blitter
        source (x=A,B,C) or destination (x=D). A modulo
        is a number that is automatically added to the
        address at the end of each line, to make the
        address point to the start of the next line. Each
        source or destination has its own modulo, allowing
        each to be a different size, while an identical
        area of each is used in the blitter operation.

LINE DRAW BLTAMOD and BLTBMOD are used as slope LINE DRAW storage registers and must be preloaded LINE DRAW with the values (4Y-4X) and (4Y) LINE DRAW respectively. Y/X= line slope. LINE DRAW BLTCMOD and BLTDMOD must both be LINE DRAW preloaded with the width (in bytes) LINE DRAW of the image into which the line is LINE DRAW being drawn (normally two times the LINE DRAW screen width in words).
SEE ALSO: Blitter programming
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