Compatibility: All
Expects: AH    06H
AL    number of lines to scroll in (0=blank entire rectangle)
BH    video attribute to be used on blank line(s)
CH,CL row,clm of lower-right corner of rectangle to scroll/blank
DH,DL row,clm of upper-left corner of rectangle to scroll/blank
Returns: (none)
Info: You may use this to scroll screen text up; that is, move each
line of text higher on the screen and add one or more blank lines
at the bottom.

This fn can be used to scroll a rectangular subset of the screen.
It may also be used to clear the entire screen or any rectangular

Notes:   The standard way to clear the screen is to set DX to 0000H, CL
to 0040:[004a]-1 (usually 79), CH to 0040:[0084] (usually 24),
BH to 07H (white-on black video attribute), and AL to 00H (to
clear the entire screen).

  To scroll the text up (as when the user presses the down
arrow), set CX and DX to cover the entire screen (or a
rectangular subset), and set AL to 1.

  CGAs: When most of the screen is a color other than black, you
should avoid using this function for scrolling.  Original CGA
BIOSes display an annoying flicker with each scroll operation.
It is usually best to write a special routine to move the text

See Also: INT 10H 07H (scroll down)
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INT 10H 06H: Scroll Up / Clear Screen Rectangle