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With the default VGA palette, setting bit 0 to enable underline will also change the text colour to blue. This means that only bits 3 (intensity) and 7 (blink) can be set concurrently with bit 0 (underline). However, since this is an MDA-compatible feature, the attribute bits not used by the MDA must be set to zero or the underline will not be shown.

The VGA hardware has the ability to enable an underline on any character that has attribute bit 0 set. VGA modes have no need for the MDA's reverse and bright attributes because foreground and background colors can be set explicitly.

^ Attribute bit 0 also enables underline, if certain other attribute bits are set to zero (see below).Ĭolors are assigned in the same way as in 4-bit indexed color graphic modes (see VGA color palette).

Therefore, if these fonts are not the same, this bit is simultaneously an additional code point bit.

^ Attribute bit 3 (foreground intensity) also selects between fonts A and B (see below).

^ Depending on the mode setup, attribute bit 7 may be either the blink bit or the fourth background color bit (which allows all 16 colors to be used as background colours).

This byte-pair scheme is among the features that the VGA inherited from the EGA, CGA, and ultimately from the MDA. The lower (or character) byte is the actual code point for the current character set, and the higher (or attribute) byte is a bit field used to select various video attributes such as color, blinking, character set, and so forth.

CGA–EGA-style 16 color palette for foreground.ĭata arrangement Text buffer Įach screen character is represented by two bytes aligned as a 16-bit word accessible by the CPU in a single operation.

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